DETAILED ACTION
Notice of Pre-AIA or AIA Status
The present application, filed on or after March 16, 2013, is being examined under the first inventor to file provisions of the AIA .
Claim Status
Claim 15 is cancelled.
Claim Objections
Claims 13 and 21 are objected to for informalities in the phrasing of the characterization. Specifically, the absence of the word "and" at the end of a list creates ambiguity, as it leaves the reader to assume that all recited properties are required in combination. Applicant is requested to insert the conjunction "and" at the end of each list in order to clarify that all claimed parameters must be met, if that is what is intended for the scope of the claims. Appropriate correction may include amending:
Claim 13 to add the word “and” to recite: “The lithium difluorophosphate according to claim 12, characterized by having a moisture content of ≤ 10 ppm, a Cl- content of ≤ 1 ppm, and the sum of the content of impurity metal ions of ≤ 2 ppm.”
Claim 21 to delete the comma after “0.8 ppm” and add the word “and” to recite: “The lithium difluorophosphate according to claim 13, characterized by having a Cl- content of ≤ 0.8 ppm[[,]] and the sum of the content of impurity metal ions of ≤ 1.5 ppm.”
Claim Rejections - 35 USC § 103
The following is a quotation of 35 U.S.C. 103 which forms the basis for all obviousness rejections set forth in this Office action:
A patent for a claimed invention may not be obtained, notwithstanding that the claimed invention is not identically disclosed as set forth in section 102, if the differences between the claimed invention and the prior art are such that the claimed invention as a whole would have been obvious before the effective filing date of the claimed invention to a person having ordinary skill in the art to which the claimed invention pertains. Patentability shall not be negated by the manner in which the invention was made.
The factual inquiries for establishing a background for determining obviousness under 35 U.S.C. 103 are summarized as follows:
1. Determining the scope and contents of the prior art.
2. Ascertaining the differences between the prior art and the claims at issue.
3. Resolving the level of ordinary skill in the pertinent art.
4. Considering objective evidence present in the application indicating obviousness or nonobviousness.
Claims 1-21 are rejected under 35 U.S.C. 103 as being unpatentable over Feng (CN112591727A) in view of Zhao (Zhao et. al., A facile synthesis of non-aqueous LiPO2F2 solution as the electrolyte additive for high performance lithium ion batteries. Chinese Chemical Letters, Volume 31, Issue 12, 2020, Pages 3209-3212, ISSN 1001-8417), Koksbang (WO0042672A2), and Wang (CN104445133A).
Regarding claim 1, Feng discloses a preparation method for lithium difluorophosphate (claim 1) that includes reacting lithium hexafluorophosphate (LiPF6) with silicon tetrachloride (SiCl4) in an anhydrous reaction environment, followed by subsequent purification to isolate the lithium difluorophosphate (LiPO2F2). Feng further discloses that the reaction is carried out under a protective atmosphere (claim 1; specification, pg. 1 lines 54-57), including glove box environments wherein the protective atmosphere is selected from one or a combination of two or more of nitrogen atmosphere, argon atmosphere, and helium atmosphere (specification, pg. 2 lines 40-41). Thus, the anhydrous limitation of claim 1 in step (1) is satisfied by Feng.
Feng further teaches sequential addition of reactants, such as in “Example 4” (specification, pg. 4 lines 45-59) wherein lithium oxalate (Li2C2O4) is first introduced into a solution containing LiPF6 and n-hexane under stirring conditions, followed by the addition of silicon tetrachloride (SiCl4), after which the reaction proceeds to form lithium difluorophosphate (LiPO2F2). The reaction sequence is being interpreted by the Examiner as:
LiPF6 + 2Li2C2O4 + SiCl4 [Wingdings font/0xE0] 2LiPO2F2 + SiF4 ↑ + 4LiCl
Further, Feng indicates that the reaction occurs immediately upon addition of silicon tetrachloride (SiCl4), thereby evidencing formation of intermediate species during the reaction sequence, although such species are not expressly isolated or characterized. Feng additionally discloses that the resulting reaction mixture is subjected to filtration, concentration, and purification steps to isolate lithium difluorophosphate (LiPO2F2).
Feng does not disclose the use of lithium carbonate in place of lithium oxalate. However, Zhao discloses reacting LiPF6 with lithium carbonate (Li2CO3) to produce lithium difluorophosphate (LiPO2F2) as represented by the reaction below (Zhao, formula (1) on pg. 3210, col. 1, para. 1):
LiPF6 + 2Li2CO3 [Wingdings font/0xE0] LiPO2F2 + 4LiF + 2CO2 ↑
Thus, Zhao discloses lithium carbonate (Li2CO3) is an art-recognized and suitable lithium-containing reagent in lithium difluorophosphate synthesis systems based on lithium hexafluorophosphate (LiPF6).
In addition, Koksbang teaches that lithium carbonate (Li2CO3) and lithium oxalate (Li2C2O4) are both recognized lithium sources and function as suitable acid scavengers that neutralize free acids and aid in achieving high product purity in terms of free acids (Koksbang, specification, pg. 3 line 38; pg. 4 lines 17-20; the oxalate and carbonate are used with LiPF6 on pg. 4 lines 30-32), thereby demonstrating that lithium carbonate (Li2CO3) is recognized as a suitable alternative to lithium oxalate (Li2C2O4) for performing the acid-scavenging function in lithium-salt synthesis and battery electrolyte systems. Thus, Koksbang teaches that lithium carbonate (Li2CO3) and lithium oxalate (Li2C2O4) perform similar functional roles in lithium-mediated reaction environments.
Therefore, in view of Zhao and Koksbang, it would have been obvious to someone of ordinary skill in the art before the effective filing date of the claimed invention to substitute lithium carbonate (Li2CO3) for lithium oxalate (Li2C2O4) in the reaction process of Feng. Such substitution would have been motivated by the recognized functional equivalence of lithium carbonate (Li2CO3) and lithium oxalate (Li2C2O4) as lithium sources and acid scavengers in lithium salt chemistry consistent with the teachings of Koksbang above, as well as the teaching of Zhao that lithium carbonate (Li2CO3) is suitable for use in LiPF6-based lithium difluorophosphate synthesis systems. Further, the substitution would represent the predictable use of prior art elements according to their established functions, and would have been reasonably expected to yield lithium difluorophosphate (LiPO2F2) as disclosed by Feng.
Although Feng already teaches sequential addition of reactants in a single reaction vessel, Feng does not explicitly separate the process into discrete staged reaction steps (1) and (2) as claimed.
Wang teaches a method for preparing lithium difluorophosphate (LiPO2F2) by performing the synthesis in separate stages, wherein a reactive intermediate is first generated in a first reaction stage under controlled reaction conditions and collected (Wang, first step is PO2F formation, specification, pg. 2 lines 39-41), after which the intermediate is then subsequently introduced into a second reaction stage to produce LiPO2F2 (Wang, second step is adding the PO2F-containing mixture to a lithium fluoride containing anhydrous HF solution which is then subjected to crystallization, filtration and drying to obtain LiPO2F2; specification, pg. 2 lines 41-44). Wang further teaches conducting the synthesis under a nitrogen atmosphere and obtaining the final LiPO2F2 product (Wang, specification, pg. 4 lines 15-28). Lastly, Wang teaches that the preparation method provides a simple process capable of producing high purity LiPO2F2 using conventional purification techniques (Wang, specification, pg. 3 lines 58-60).
Therefore, in view of Wang, it would have been obvious to someone of ordinary skill in the art before the effective filing date of the claimed invention to further modify the preparation method of Feng (hereby referred to as “modified Feng” as previously modified by Zhao and Koksbang above) to separately form the reaction intermediate prior to reacting the intermediate with the lithium carbonate dispersion (i.e. allowing the initial reaction between lithium hexafluorophosphate (LiPF6) and silicon tetrachloride (SiCl4) to proceed prior to the introduction of lithium carbonate (Li2CO3)), as suggested by Wang, because Wang teaches that multi-stage synthesis is a known and suitable preparation method for producing lithium difluorophosphate (LiPO2F2) using conventional downstream purification techniques. Such modification would merely apply Wang’s multi-stage process arrangement to the modified preparation method of Feng while retaining the otherwise taught reaction chemistry and purification process, and would represent the predictable use of prior art elements according to their established functions. As such, one of ordinary skill in the art would have arrived at the multi-stage preparation method of claim 1, including separately forming the reaction intermediate in step (1) and subsequently reacting the intermediate with the lithium carbonate dispersion in step (2) to produce lithium difluorophosphate (LiPO2F2), as claimed.
Accordingly, step (1) of claim 1 is taught or rendered obvious by Feng, which discloses reacting lithium hexafluorophosphate (LiPF6) with silicon tetrachloride (SiCl4) under anhydrous conditions with sequential addition to form a reactive reaction mixture in which intermediate species are formed during the reaction progression. Regarding the intermediate species, Feng does not explicitly write intermediates. However, one of ordinary skill in the art would have expected that lithium hexafluorophosphate (LiPF6) would first undergo a halogenation reaction with the silicon tetrachloride (SiCl4), followed by reaction with lithium oxalate (Li2C2O4) to produce lithium difluorophosphate (LiPO2F2) and lithium chloride (LiCl); therefore, the halogenation step of LiPF6 with SiCl4 to form the intermediate LiPF2Cl4 as claimed in step (1) is an inherent chemical transition in both the claimed method and the reaction progression implied in Feng. Regarding the limitation “…and degassing and removing impurities to obtain a lithium difluorotetrachloro phosphate solution…” for step (1), Feng inherently performs this step because Feng teaches "replacing the air in the flask with nitrogen" and subsequently connecting an exhaust gas absorption device (Feng, specification, “Example 1”, pg. 3 lines 59-60); as such, replacing the ambient air with nitrogen serves as a physical purge that removes (degasses) dissolved atmospheric gases, while the exhaust device continuously draws off and removes volatile impurities and gaseous byproducts generated as the reaction proceeds.
Step (2) is taught or rendered obvious by the combined teachings of Feng, Zhao, and Koksbang, which collectively teach reacting the LiPF6/SiCl4 reaction mixture with a lithium-containing reagent, and further render obvious substitution of lithium carbonate (Li2CO3) for lithium oxalate (Li2C2O4) as a predictable variation with a reasonable expectation of success. Further, in reference to the “…filtering to obtain a filter cake mixture of lithium difluorophosphate and lithium chloride” limitation of step (2) of the reaction process, Feng discloses in “Example 4” that the lithium oxalate was quickly added to the reaction flask, SiCl4 was subsequently added, and the reaction occurred immediately. After 20 hours of reaction at room temperature the reaction was completed, and the filter cake containing lithium difluorophosphate and lithium chloride was then obtained by filtration (“Example 4” on pg. 4 line 52).
Regarding the limitation “dropwise adding the obtained lithium difluorotetrachloro phosphate solution” in step (2), Feng does not explicitly state that the addition of solutions is performed dropwise. However, it is well-established that addition techniques such as “dropwise” versus rapid or bulk addition is a matter of routine optimization for a person having ordinary skill in the art. The primary purpose of dropwise addition is to control the rate of reaction, manage exotherms, and prevent localized reactant concentration spikes. Because the Applicant’s specification does not define "dropwise" and fails to articulate any unexpected, critical, or unobvious result stemming from dropwise addition specifically, the limitation constitutes routine optimization. When a technique has been used to improve one chemical process and a person of ordinary skill in the art would recognize that it would improve similar reactions in the same way, using the technique is rendered obvious. Thus, it would have been obvious to a person of ordinary skill in the art to add the intermediate phosphate solution to the carbonate dispersion (consistent with the modification of Feng above) in a dropwise manner in order to safely control the speed of the reaction and optimize the yield. Therefore, the limitation of dropwise addition fails to patentably distinguish the claimed method from modified Feng.
Step (3) of claim 1 is rendered obvious by the combined teachings of Feng and conventional purification practices in lithium salt synthesis systems. Feng discloses that after completion of the reaction, the resulting mixture is subjected to separation and purification steps to isolate lithium difluorophosphate (LiPO2F2). In terms of the limitation “pulping the filter cake mixture with ethyl acetate,” Feng teaches recovering the solid product, which in this case is the filter cake mixture of lithium difluorophosphate (LiPO2F2) and lithium chloride (LiCl) obtained from step (2), and adding it to a polar non-aqueous solvent for stirring and dissolving to obtain a slurry liquid. Feng explicitly discloses that this polar non-aqueous solvent is selected from one or a combination of two or more of methanol, ethanol, propanol, n-butanol, ethyl acetate, and acetonitrile (specification, pg. 2 lines 51-52). Furthermore, Feng utilizes ethyl acetate in “Example 1” and “Example 2” (pg. 4 lines 1-4 and 19-21), demonstrating its general operability in the reaction methodology. Thus, Feng teaches solvent-based treatment of an isolated product solution, including the use of ethanol and ethyl acetate, consistent with solvent pulping or washing off the reaction residue. Then, the resulting product solution was concentrated to remove solvent, and subjected to crystallization through solvent manipulation, including addition of a second non-polar solvent system to induce isolation of lithium difluorophosphate (LiPO2F2) as a solid product (Feng, after filtering to remove insoluble material, the mixture is sequentially concentrated and crystallized, specification, pg. 3 lines 1-11). Accordingly, step (3) would have been obvious as it represents routine, post-reaction workup steps commonly employed in lithium salt synthesis, including filtration, solvent washing or pulping of the crude product mixture, concentration of the resulting solution, and crystallization though solvent addition to isolate the desired lithium difluorophosphate (LiPO2F2) product.
Therefore, it would have been obvious to someone of ordinary skill in the art before the effective filing date of the claimed invention to modify the process of Feng (hereby further referred to as "modified Feng”) in view of Zhao, Koksbang, and Wang, to arrive at the claimed method for preparing lithium difluorophosphate (LiPO2F2). The combination of all references would merely involve the predictable use of prior art elements according to their established functions, and would yield no more than what would have been expected by one of ordinary skill in the art in view of the teachings of the cited references.
Regarding claim 2, modified Feng teaches all features of claim 1 as described above, but Feng does not expressly disclose that the charge molar ratio of lithium hexafluorophosphate, silicon tetrachloride, and lithium carbonate is 1:(1-1.5): (2-2.5). However, Feng discloses the molar ratio of the lithium hexafluorophosphate, oxalate and silicon tetrachloride is 1: (1-1.5): (0.55-0.75). Feng further demonstrates (in working Examples 1-4) that varying the types of oxalates and reaction conditions results in a lithium difluorophosphate (LiPO2F2) product of 99.8% to 99.9% purity and yields ranging from 86.1% to 95.4% (specification, pg 3-4). Further, as previously applied to claim 1, it would have been obvious to a person of ordinary skill in the art to substitute lithium carbonate for the oxalate source taught by Feng, with Koksbang providing the motivation to use lithium carbonate as an acid scavenger.
It is well-established that where the general conditions of a claim are disclosed in the prior art, discovering the optimum or workable ranges involves only routine optimization (see MPEP §2144.05). Feng discloses that varying the starting reagents in the mixture directly impacts the yield (from 86.1% to 95.4%) and purity (from 99.8%-99.9%), thereby rendering the reactant molar proportions result-effective variables. Thus, a person of ordinary skill in the art would have routinely optimized the relative amounts of reactants to ensure complete conversion or to balance cost against yield, as standard in chemical synthesis.
Regarding claim 3, modified Feng teaches the preparation method for lithium difluorophosphate according to claim 1 as described above. Feng further teaches the molar ratio of the lithium hexafluorophosphate (LiPF6), oxalate, and silicon tetrachloride (SiCl4) is 1:1-1.5: 0.55-0.75, and that the concentration of lithium hexafluorophosphate (LiPF6) in “Example 4” is ~1.12 mol/L, which closely approaches but falls just outside the claimed range of 1.5 to 4.0 mol/L.
However, Feng expressly discloses in Examples 1-4 that varying the starting reagents in the mixture directly impacts the yield (from 86.1% to 95.4%) and purity (from 99.8% to 99.9%) (specification, pg 3-4), thereby rendering the reactant molar concentrations result-effective variables. Thus, a person of ordinary skill in the art would have routinely optimized the relative amounts of reactants in order to ensure complete conversion or to balance cost against yield, as standard in chemical synthesis.
Regarding claim 4, as set forth in the rejection of claim 1 above, Feng as applied therein discloses a method for preparing lithium difluorophosphate (LiPO2F2) using lithium hexafluorophosphate (LiPF6) with silicon tetrachloride (SiCl4) under anhydrous conditions in a single reaction vessel, wherein reactants are sequentially introduced and the reaction proceeds to form lithium difluorophosphate (LiPO2F2) prior to purification. Feng further discloses the organic solvent in step (1) (i.e. the first non-aqueous solvent of claim 4) may be selected from a combination of one or more of dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, ethylene carbonate, propylene carbonate, toluene, xylene, n-hexane, n-pentane, heptane, dichloromethane, and chloroform (specification, pg. 2 lines 17-19).
Regarding the temperature, Feng, as applied to claim 1, further discloses that the reaction can be carried out at temperatures ranging from 5°C - 80°C, explicitly including 40°C, 50°C, 60°C, 70°C, and 80°C, in order to obtain high yield and high purity (specification, pg. 2 lines 21-33), which overlaps substantially with the claimed range of 20°C - 100°C. Feng also notes that the reaction temperature may be adjusted (i.e. increased) to be within a working range of 15°C - 80°C in order to obtain a faster reaction rate (specification, pg. 2 lines 21-23), and discloses working embodiments conducted at room temperature, which encompass temperatures of 15°C - 30°C (specification, pg. 2 lines 29-30). Feng further teaches that carrying out the reaction at room temperature provides advantages including reduced energy consumption and improved control of silicon tetrachloride (SiCl4) reactivity and gas evolution rate (specification, pg. 2 lines 30-33).
Therefore, in view of these teachings, one of ordinary skill in the art would have recognized that reaction temperature is a result-effective variable in the lithium difluorophosphate (LiPO2F2) synthesis system of Feng, as applied in claim 1, because it influences reaction rate, gas evolution behavior, and overall process operability while still producing the same lithium difluorophosphate (LiPO2F2) product. Where a parameter is recognized as a result-effective variable, optimization of that parameter within a known or overlapping range is considered an obvious matter of routine experimentation. Accordingly, it would have been obvious to select a reaction temperature within the claimed range of 20°C - 100°C, including temperatures overlapping the disclosed range of Feng, as part of routine process optimization to achieve desired reaction control and operational efficiency. Thus, such optimization would have been expected to yield the predictable results of the successful formation of lithium difluorophosphate (LiPO2F2) under the same reaction conditions disclosed in Feng, without altering the nature of the reaction or the product formed.
Regarding claim 5, as set forth in the rejection of claim 1 above, it would have been obvious to modify the sequential one-pot synthesis of Feng by (1) substituting lithium carbonate for lithium oxalate in view of Zhao and Koksbang, and (2) separating the reaction into discrete reaction stages in view of Wang, thereby arriving at the claimed staged synthesis of lithium difluorophosphate (LiPO2F2).
Feng further teaches that the that the reaction can be carried out at temperatures ranging from 5°C - 80°C, explicitly including 40°C, 50°C, 60°C, 70°C, and 80°C, in order to obtain high yield and high purity (specification, pg. 2 lines 21-33). Feng further discloses working embodiments (specification, Examples 1-4, pg. 3-4) conducted at approximately room temperature, which encompass temperatures of 15°C - 30°C (specification, pg. 2 lines 29-30), and teaches that carrying out the reaction at room temperature provides advantages including reduced energy consumption and improved control of silicon tetrachloride (SiCl4) reactivity and gas evolution rate (specification, pg. 2 lines 30-33), thereby improving the practicality and controllability of the reaction.
Therefore, in view of these teachings, one of ordinary skill in the art would have recognized that reaction temperature is a result-effective variable in the lithium difluorophosphate (LiPO2F2) synthesis system of Feng, as applied in claim 1, because it influences reaction rate, gas evolution behavior, and overall process operability while still producing the same lithium difluorophosphate (LiPO2F2) product. Where a parameter is recognized as a result-effective variable, optimization of that parameter within a known or overlapping range is considered an obvious matter of routine experimentation. Accordingly, it would have been obvious to select a reaction temperature for the second stage of the modified process of claim 1, including a temperature within the claimed range of 30°C - 80°C through routine optimization to achieve the desired balance of reaction control, process efficiency, and product formation. Because the claimed range substantially overlaps with the temperature range disclosed by Feng, selection of a temperature within the overlapping range would have been a matter of routine optimization yielding the predictable results of the successful formation of lithium difluorophosphate (LiPO2F2) within the modified synthesis of claim 1.
Regarding claim 6, modified Feng teaches all features of claim 1 as described above. Feng further teaches the preparation method for lithium difluorophosphate (LiPO2F2) using non-aqueous solvents, specifically reciting cyclic carbonates (e.g. ethylene carbonate and propylene carbonate) and chain carbonates (e.g. dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate), and additionally toluene, xylene, n-hexane, n-pentane, heptane, and chloroform or a combination thereof (specification, pg. 2, lines 17-19). Feng also explicitly discloses in working Examples 1-4 the use of dimethyl carbonate, ethyl acetate, dichloromethane, toluene, methanol, n-hexane, and ethanol in various combinations for the first and second solvents (specification, Examples 1-4, pg. 3-4).
Regarding claim 7, modified Feng teaches all features of claim 1 as described above, and further teaches in step (3) of the preparation method that after the filtration step, the filter cake mixture, which contains lithium difluorophosphate (LiPO2F2) and lithium chloride (LiCl), is pulped with ethanol for 5 h, which overlaps with the claimed range of 3 to 5 h (specification, “Example 4”, pg. 4, lines 52-53). Feng also discloses the time for stirring and dissolving is in a range of 2-5 h (specification, pg. 2, line 57). Regarding the solvent, although Example 4 uses ethanol during the pulping step, Feng expressly teaches that ethyl acetate is a suitable solvent for the purification process (specification, pg. 2, lines 51-52; ethyl acetate is also used in “Example 1” and “Example 2” on pg. 3-4).
Feng does not expressly disclose that in step (3) when pulping the filter cake mixture, the mass ratio of the filter cake mixture to ethyl acetate is 1:(1-2).
Feng does, however, teach selecting the amount of polar non-aqueous solvent used during the stirring and dissolving step (which includes the pulping step) is determined by the theoretical production of LiPO2F2 (specifically 10-15 mL per gram) (for every theoretical calculated gram of LiPO2F2 produced, 10-15 mL of a polar non-aqueous solvent is added; specification, pg. 2, lines 54-55). By teaching that the solvent quantity is a variable dictated by the scale of the LiPO2F2 product, Feng recognizes that the quantity of solvent (i.e. solvent volume in this case) impacts the purification outcome in terms of purification efficiency and yield (specification, pg. 2, lines 47-49). Thus, Feng teaches that the solvent quantity used during the pulping step is selected based on the requirements of the purification process rather than being a fixed amount. Therefore, one of ordinary skill in the art would have understood the amount of solvent used during the pulping step to be a result-effective variable that could be optimized depending on the desired purification conditions. One of ordinary skill in the art would have also understood that varying the ratio of solvent-to-filter cake mixture changes the concentration gradient, directly affecting the dissolution and removal of soluble impurities in the final product.
Therefore, it would have been obvious to someone of ordinary skill in the art before the effective filing date of the claimed invention to optimize the amount of ethyl acetate used during the pulping step through routine experimentation in order to provide sufficient solvent to remove soluble impurities from the filter cake while minimizing solvent waste, downstream solvent recovery loads, and manufacturing costs in order to achieve an efficient purification process. In addition, by adjusting the solvent quantity according to these standard purification principles, a person of ordinary skill in the art would have arrived at the claimed mass ratio of the filter cake mixture to ethyl acetate of 1:(1-2) through routine experimentation and optimization, while retaining the limitations of the otherwise taught purification process.
Regarding claim 8, modified Feng teaches all features of claim 1 as describe above, including the purification process of step (3). The instant claim 8 requires that in step (3), the non-polar solvent is one or a combination of two or more selected from the group consisting of n-hexane, n-pentane, cyclohexane, heptane, dichloromethane, trichloromethane, and 1,2-dichloroethane.
Feng teaches that, following the completion of the reaction, the product is purified by filtration, dissolution of the filter cake, concentration, and crystallization (specification, pg. 3 lines 21-26). Comparative Example 1 of Feng expressly teaches adding 150 mL of dichloromethane as the poor solvent for the crystallization step, followed by stirring, crystallization, filtration, and drying to obtain lithium difluorophosphate (LiPO2F2) (specification, pg. 5 lines 7-10). Accordingly, modified Feng teaches crystallizing LiPO2F2 by adding dichloromethane, which is expressly recited in the claimed Markush group of solvents. Thus, it would have been obvious to use the expressly taught dichloromethane during the crystallization step of the modified preparation method.
Regarding claim 9, modified Feng teaches all features of claim 1, and further teaches the preparation method for lithium difluorophosphate characterized in that in step (3), the step of crystallization includes stirring and crystallization under the condition of -10 to 0°C (specification, pg. 3 lines 8-9), which overlaps with the claimed range of 0°C to 5°C. Further, Feng discloses in working Examples 1-4 and Comparative Example 1 that the crystallizing steps occur at a temperature of -5°C, -8°C, -10°C, -9°C and 5-10°C, respectively (specification, pg. 3-5).
Regarding claim 10, modified Feng teaches all features of claim 1, and further teaches the preparation method for lithium difluorophosphate characterized in that in step (3), after crystallization, filtration is also performed to obtain a filter cake, and then the filter cake is dried to obtain lithium difluorophosphate at a temperature of 90°C (after stirring to crystallize, the solution was filtered and dried in a glove box at 90°C for 24h; specification, pg. 4, “Example 4” lines 54-58), which falls within the claimed range. In addition, Feng explicitly discloses the drying temperature is 80°C to 120°C (specification, pg. 3 line 11), which is identical to the claimed range.
Regarding claim 11, modified Feng teaches all features of claim 1, and further teaches the preparation method for lithium difluorophosphate characterized in that in both step (1) and step (2), the reaction is carried out in an atmosphere of inert gas, wherein the inert gas is one or more gases selected from the group consisting of nitrogen, argon, and helium. Specifically, Feng discloses that the reaction (i.e. steps (1) and (2) of claim 1) is carried out under a protective atmosphere (claim 1; specification, pg. 1 lines 54-57), including glove box environments wherein the protective atmosphere is selected from one or a combination of two or more of nitrogen atmosphere, argon atmosphere, and helium atmosphere (specification, pg. 2 lines 40-41).
Regarding claim 12, modified Feng teaches all features of claim 1, and further teaches the preparation method for lithium difluorophosphate (LiPO2F2) characterized in that the lithium difluorophosphate (LiPO2F2) has a purity of ≥ 99.8%. Specifically, Feng discloses the purity of the final lithium difluorophosphate (LiPO2F2) product in working Examples 1-2 and 4 was 99.8%, and Example 3 was 99.9% as measured by fluorine spectrum (specification, pg. 3-5). Therefore, Feng teaches the lithium difluorophosphate (LiPO2F2) having a purity of ≥ 99.8%.
Feng does not expressly disclose a free acid content of ≤ 50 ppm.
However, as discussed in the rejection of claim 1, modified Feng uses lithium carbonate as the acid scavenger. Koksbang teaches that lithium carbonate and lithium oxalate function as acid scavengers for neutralizing free acids (specification, pg. 4 lines 17-20) in LiPF6-based electrolyte systems (specification, pg. 4 lines 30-35) and further discloses varying proportions of lithium carbonate and lithium oxalate in working examples and disclosed ranges (specification, pg. 5-7, Examples 1-5 and their respective comparative examples; claims 8 and 10 for disclosed ranges of lithium oxalate and lithium carbonate). Accordingly, one of ordinary skill in the art would have recognized that the amount and composition of the acid scavenger affect the neutralization of free HF and, consequently, the residual free acid content of the final lithium difluorophosphate (LiPO2F2) product and, therefore, would have been recognized by one of ordinary skill in the art as result-effective variables suitable for routine optimization.
Furthermore, because Feng teaches obtaining a high-purity lithium difluorophosphate (LiPO2F2) product through the disclosed synthesis and purification process, one of ordinary skill in the art would have been motivated to optimize the synthesis conditions to maximize product purity while minimizing residual impurities, including free residual acid. Therefore, it would have been obvious to someone of ordinary skill in the art before the effective filing date of the claimed invention to optimize the amount and composition of the acid scavenger through routine experimentation to further reduce residual free acid while maintaining efficient lithium salt synthesis and high product purity, thereby arriving at a suitable free acid content, including the claimed value of ≤ 50 ppm. Such optimization would have resulted in the routine optimization of recognized result-effective variables and the predictable improvement of a known process. Accordingly, it would have been obvious to optimize the amount and composition of the acid scavenger utilized in the preparation method of modified Feng through routine experimentation to obtain lithium difluorophosphate (LiPO2F2) having high purity and reduced residual free acid while retaining the otherwise taught synthesis and purification process.
Regarding claim 13, modified Feng teaches all features of claim 12, including preparing lithium difluorophosphate (LiPO2F2) with the claimed method steps (1)-(3). Feng further teaches conducting the reaction under a protective atmosphere (i.e. anhydrous conditions) selected from one or a combination of two or more of nitrogen atmosphere, argon atmosphere, and helium atmosphere (specification, pg. 2 lines 40-41).
Modified Feng does not expressly disclose the lithium difluorophosphate (LiPO2F2) product having a moisture content of ≤ 10 ppm, a Cl- content of ≤ 1 ppm, and the sum of the content of impurity metal ions is ≤ 2 ppm.
Regarding the moisture content, Feng further teaches drying the crystallized LiPO2F2 product at a temperature of 80-120°C for 10-24 h (specification, pg. 3 line 11). Feng also teaches carrying out the reaction under anhydrous conditions (i.e. the protective atmosphere) while obtaining a high purity LiPO2F2 product. Accordingly, one of ordinary skill in the art would have recognized the drying conditions, including drying temperature, time, and moisture-control conditions during synthesis and purification, affect the residual moisture content of the final LiPO2F2 product and therefore would have recognized these as result-effective variables. Because Feng teaches obtaining a high purity LiPO2F2 product, one of ordinary skill in the art would have been motivated to optimize the drying and moisture-control conditions through routine experimentation to maximize product purity while minimizing residual moisture, thereby arriving at a suitable moisture content, including the claimed value of ≤ 10 ppm.
Regarding the Cl- content, Feng further teaches purifying the LiPO2F2 by obtaining a filter cake containing LiPO2F2 lithium chloride (LiCl), followed by pulping the filter cake with solvent, filtration, concentration, crystallization, and then drying to obtain a high purity LiPO2F2 product (specification, pg. 3 lines 21-26). Accordingly, one of ordinary skill in the art would have understood that the purification process is directed, at least in part, to the removal of residual lithium chloride (LiCl) and other impurities remaining after synthesis. Therefore, one of ordinary skill in the art would have recognized that the purification conditions, including the pulping, filtration, concentration, crystallization, and drying conditions, affect the residual Cl- content of the final product and therefore are result-effective variables. Because Feng teaches obtaining a high purity LiPO2F2 product, one of ordinary skill in the art would have been motivated to optimize the purification conditions through routine experimentation to maximize purity while minimizing residual Cl- containing impurities, thereby arriving at a suitable Cl- content, including the claimed value of ≤ 1 ppm.
Regarding the claimed sum of the content of impurity metal ions, the Applicant specification does not provide a special definition of “impurity metal ions.” Therefore, under the broadest reasonable interpretation, the term “impurity metal ions” reasonably encompasses residual trace metal contaminants remaining in the LiPO2F2 product following synthesis and purification. Feng teaches obtaining a high purity LiPO2F2 product through the modified synthesis and purification process (as modified in the rejection of claim 1 above); accordingly, one of ordinary skill in the art would have understood that the purification and contamination-control conditions affect the overall residual impurity profile of the final LiPO2F2 product and therefore are result-effective variables. Because Feng teaches that the objective of the disclosed purification process is to obtain a high purity LiPO2F2 product, one of ordinary skill in the art would have been motivated to optimize the purification conditions through routine experimentation to maximize LiPO2F2 product purity while minimizing residual impurities remaining after synthesis, including residual trace metal impurities, including a sum of the content of impurity metal ions of ≤ 2 ppm.
Regarding claim 14, Feng discloses a non-aqueous electrolyte battery (specification, pg. 1 lines 49-52) characterized by comprising a positive electrode, a negative electrode, and an electrolyte comprising the lithium difluorophosphate (LiPO2F2) of claim 12. Specifically, Feng discloses a non-aqueous electrolyte battery comprising lithium difluorophosphate (LiPO2F2) for use with active electrodes (specification, pg. 1 lines 19-25 and 49-52). While Feng does not expressly name the specific types or compositions of the positive and negative electrodes, a battery inherently requires both a positive electrode and a negative electrode to facilitate the flow of electrical current. Therefore, providing a battery with an electrolyte necessarily encompasses the electrodes with which the electrolyte interacts. Accordingly, it would have been obvious to someone of ordinary skill in the art before the effective filing date of the claimed invention to combine the claimed electrolyte comprising the lithium difluorophosphate (LiPO2F2) of claim 12 with conventional positive and negative electrodes, as Feng expressly discloses that the electrolyte additive is designed to interact with active electrode surfaces in order to prevent deterioration and improve cycle performance (specification, pg. 1 lines 23-25). Thus, modified Feng discloses all limitations of claim 14.
Regarding claim 16, as set forth in the rejection of claim 1 above, Feng as applied therein discloses a method for preparing lithium difluorophosphate (LiPO2F2) using lithium hexafluorophosphate (LiPF6) with silicon tetrachloride (SiCl4) under anhydrous conditions in a single reaction vessel, wherein reactants are sequentially introduced and the reaction proceeds to form lithium difluorophosphate (LiPO2F2) prior to purification.
Feng, as applied to claim 1, further discloses that the reaction is carried out under a protective atmosphere (claim 1; specification, pg. 1 lines 54-57), including glove box environments wherein the protective atmosphere is selected from one or a combination of two or more of nitrogen atmosphere, argon atmosphere, and helium atmosphere (pg. 2 lines 40-41), which teaches the limitation regarding the non-reactive gas used in step (1) to degas the solution and remove impurities.
For the limitation of step (1) regarding the temperature range, Feng discloses that the reaction can be carried out at temperatures ranging from 5°C - 80°C, explicitly including 40°C, 50°C, 60°C, 70°C, and 80°C, in order to obtain high yield and high purity, which overlaps with the claimed range of 60°C - 120°C. Therefore, one of ordinary skill in the art would have recognized that reaction temperature is a result-effective variable in the lithium difluorophosphate (LiPO2F2) synthesis system of Feng, as applied in claim 1, because it influences reaction rate, gas evolution behavior, and overall process operability while still producing the same lithium difluorophosphate (LiPO2F2) product. Where a parameter is recognized as a result-effective variable, optimization of that parameter within a known or overlapping range is considered an obvious matter of routine experimentation. Accordingly, it would have been obvious to select a reaction temperature for step (1) of the reaction within the claimed range of 60°C - 120°C, including temperatures overlapping the disclosed range of Feng, as part of routine process optimization to achieve desired reaction control and operational efficiency. Such routine optimization would have been expected to yield the predictable results of the successful formation of lithium difluorophosphate (LiPO2F2) under the same reaction conditions disclosed in Feng, without altering the nature of the reaction or the product formed.
Regarding claim 17, modified Feng teaches all features of claim 16, and further teaches the preparation method for lithium difluorophosphate (LiPO2F2) characterized in that the non-reactive gas is one or more gases selected from the group consisting of nitrogen, argon, helium, and combination thereof. Specifically, as set forth in the rejection of claim 1 above, Feng as applied therein discloses a method for preparing lithium difluorophosphate (LiPO2F2) using lithium hexafluorophosphate (LiPF6) with silicon tetrachloride (SiCl4) under anhydrous conditions in a single reaction vessel, wherein reactants are sequentially introduced and the reaction proceeds to form lithium difluorophosphate (LiPO2F2) prior to purification. Feng further discloses that the reaction is carried out under a protective atmosphere (claim 1; specification, pg. 1 lines 54-57), including glove box environments wherein the protective atmosphere is selected from one or a combination of two or more of nitrogen atmosphere, argon atmosphere, and helium atmosphere (specification, pg. 2 lines 40-41). Thus, modified Feng teaches all limitations of claim 17 regarding the non-reactive gas used in step (1) to degas the solution and remove impurities.
Such optimization of recognized result effective variables would result in the routine optimization of a known process to improve product purity and would represent the predictable use of prior art elements according to their established functions. Accordingly, it would have been obvious to optimize the drying conditions and purification conditions of modified Feng through routine experimentation to obtain high purity lithium difluorophosphate (LiPO2F2) having reduced residual moisture and residual impurities while retaining the otherwise taught synthesis and purification process.
Regarding claim 18, modified Feng teaches all features of claim 1, including a preparation method for lithium difluorophosphate wherein a lithium carbonate dispersion is prepared in step (2) by mixing lithium carbonate with a second non-aqueous solvent. Regarding the second non-aqueous solvent (and consistent with the rejection of claim 6 above), Feng discloses the use of cyclic carbonates (e.g. ethylene carbonate and propylene carbonate) and chain carbonates (e.g. dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate), and additionally toluene, xylene, n-hexane, n-pentane, heptane, and chloroform or a combination thereof (specification, pg. 2, lines 17-19). Feng also explicitly discloses in working Examples 1-4 the use of dimethyl carbonate, ethyl acetate, dichloromethane, toluene, methanol, n-hexane, and ethanol in various combinations for the first and second solvents (specification, Examples 1-4, pg. 3-4).
Regarding the claimed limitation of step (2) wherein the mass ratio of lithium carbonate to the second non-aqueous solvent is between 1:3 and 1:5, and consistent with the modification discussed in the rejection of claim 1 above in terms of substituting the lithium carbonate for lithium oxalate in the reaction, the 60 g quantity disclosed for lithium oxalate in Feng’s Example 4 (specification, “Example 4” on pg. 4, line 48) is herein applied to lithium carbonate, while the remaining reaction conditions of Example 4, including the amount of the second non-aqueous solvent, are maintained. Feng’s Example 4 further uses approximately 264.2 g of the second non-aqueous solvent, which in this case is n-hexane (ρn-hexane at room temperature = 0.6606 g/mL and the volume of n-hexane is 400 mL; solvent mass = Vρ). Accordingly, modified Example 4 utilizes a mass ratio of lithium carbonate to second non-aqueous solvent of approximately 1: 4.4 (mass ratio =
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), which falls within the claimed range of 1:3 to 1:5. Therefore, claim 18 is obvious over modified Feng.
Regarding claim 19, modified Feng teaches all features of claim 1, including step (3). Feng discloses in Example 4 obtaining a filter cake containing lithium difluorophosphate (LiPO2F2) and lithium chloride (LiCl) by filtration, adding the filter cake to an ethanol solution, stirring, and filtering to obtain an ethanol solution containing LiPO2F2. Feng further discloses distilling the resulting filtrate (an ethanol solution containing LiPO2F2) under reduced pressure at 60°C until the solution is concentrated to a saturated state, followed by crystallization and filtration to obtain LiPO2F2 (specification, pg. 4 lines 52-57). One of ordinary skill in the art would have understood distillation under reduced pressure to be vacuum distillation. Furthermore, the disclosed distillation temperature of 60°C falls within the claimed range of 40°C to 80°C.
Accordingly, modified Feng teaches the claimed distillation requirements for step (3). Therefore, it would have been obvious to a person of ordinary skill in the art to concentrate the pulping solution by subjecting the filtrate to vacuum distillation within the claimed temperature range.
Regarding claim 20, modified Feng, as discussed in the rejection of claim 12 above, teaches the preparation method for lithium difluorophosphate (LiPO2F2) according to steps (1)-(3) of claim 1, and further teaches obtaining a high purity LiPO2F2 product. As further discussed in the rejection of claim 12, Koksbang teaches that lithium carbonate and lithium oxalate function as acid scavengers for neutralizing free acids (specification, pg. 4 lines 17-20) in LiPF6-based electrolyte systems (specification, pg. 4 lines 30-35) and further discloses varying proportions of lithium carbonate and lithium oxalate in working examples and disclosed ranges (specification, pg. 5-7, Examples 1-5 and their respective comparative examples; claims 8 and 10 for disclosed ranges of lithium oxalate and lithium carbonate). Accordingly, one of ordinary skill in the art would have recognized that the amount and composition of the acid scavenger affect the neutralization of free HF and, consequently, the residual free acid content of the final lithium difluorophosphate (LiPO2F2) product and, therefore, would have been recognized by one of ordinary skill in the art as result-effective variables suitable for routine optimization.
Claim 19 recites that the lithium difluorophosphate (LiPO2F2) product has a free acid content of ≤ 25 ppm. Although modified Feng does not expressly disclose this numerical value, it would have been obvious to someone of ordinary skill in the art before the effective filing date of the claimed invention to further optimize the amount and composition of the acid scavenger through routine experimentation to further reduce residual free acid while maintaining efficient lithium salt synthesis and high product purity, thereby arriving at a suitable free acid content, including the claimed value of ≤ 25 ppm. Such optimization would have resulted in the routine optimization of recognized result-effective variables and the predictable improvement of a known process. Accordingly, it would have been obvious to optimize the amount and composition of the acid scavenger utilized in the preparation method of modified Feng through routine experimentation to obtain lithium difluorophosphate (LiPO2F2) having high purity and a reduced residual free acid content of ≤ 25 ppm, while retaining the otherwise taught synthesis and purification process.
Regarding claim 21, modified Feng, as discussed in the rejection of claim 13 above, teaches the preparation method for lithium difluorophosphate (LiPO2F2) according to steps (1)-(3) of claim 1, and further teaches obtaining a high purity LiPO2F2 product through the disclosed purification process. As further discussed in the rejection of claim 13, one of ordinary skill in the art would have recognized that the purification conditions, including the pulping, filtration, concentration, crystallization, and drying conditions, affect the residual impurity profile of the final LiPO2F2 product (including residual chloride-containing impurities and residual trace metal impurities), and therefore are result-effective variables.
Claim 21 further recites the lithium difluorophosphate is characterized by having a Cl- content of ≤ 0.8 ppm and the sum of the content of impurity metal ions of ≤ 1.5 ppm. Although modified Feng does not expressly disclose these numerical values, it would have been obvious to someone of ordinary skill in the art before the effective filing date of the claimed invention to further optimize the purification conditions through routine experimentation to maximize LiPO2F2 product purity while minimizing residual impurities remaining after synthesis, thereby arriving at suitable residual impurity levels, including a Cl- content of ≤ 0.8 ppm and a sum of the content of impurity metal ions of ≤ 1.5 ppm. Such optimization would have resulted in the routine optimization of recognized result-effective variables and the predictable improvement of a known process. Accordingly, it would have been obvious to optimize the purification conditions of modified Feng through routine experimentation to obtain lithium difluorophosphate (LiPO2F2) having the claimed chloride ion content and impurity metal ion content while retaining the otherwise taught synthesis and purification process.
Conclusion
The prior art made of record and not relied upon is considered pertinent to applicant's disclosure:
Park (US20180301739A1): appears to disclose a liquid electrolyte for a battery that includes a lithium salt and a mixed non-aqueous solvent, wherein the non-aqueous solvent includes cyclic ether.
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/A.R.O./Examiner, Art Unit 1789
/JENNIFER A BOYD/Supervisory Patent Examiner, Art Unit 1786
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