Prosecution Insights
Last updated: April 19, 2026
Application No. 18/044,742

PURIFICATION OF BIS (FLUOROSULFONYL) IMIDE SALT

Non-Final OA §103§112
Filed
Mar 09, 2023
Examiner
QIAN, YUN
Art Unit
1738
Tech Center
1700 — Chemical & Materials Engineering
Assignee
Solvay SA
OA Round
1 (Non-Final)
54%
Grant Probability
Moderate
1-2
OA Rounds
3y 3m
To Grant
75%
With Interview

Examiner Intelligence

Grants 54% of resolved cases
54%
Career Allow Rate
588 granted / 1081 resolved
-10.6% vs TC avg
Strong +20% interview lift
Without
With
+20.3%
Interview Lift
resolved cases with interview
Typical timeline
3y 3m
Avg Prosecution
60 currently pending
Career history
1141
Total Applications
across all art units

Statute-Specific Performance

§101
0.1%
-39.9% vs TC avg
§103
44.3%
+4.3% vs TC avg
§102
16.8%
-23.2% vs TC avg
§112
26.8%
-13.2% vs TC avg
Black line = Tech Center average estimate • Based on career data from 1081 resolved cases

Office Action

§103 §112
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 . In the event the determination of the status of the application as subject to AIA 35 U.S.C. 102 and 103 (or as subject to pre-AIA 35 U.S.C. 102 and 103) is incorrect, any correction of the statutory basis (i.e., changing from AIA to pre-AIA ) for the rejection will not be considered a new ground of rejection if the prior art relied upon, and the rationale supporting the rejection, would be the same under either status. Response to Election/Restrictions Applicant’s election with traverse of Group I claims 1-12 in the reply filed on 11/10/2025 is acknowledged. Applicants’ arguments are not found persuasive because the office action as discussed below did point out the special technical feature linking the inventions, including bis(fluorosulfonyl)imide, 1st and 2nd solvents, lithium bis(fluorosulfonyl)imide taught by Kim et al (WO 2020/099527 A1) and Yang et al. (CN 110697668 A), does not provide a contribution over the prior art, and no single general inventive concept exists. Therefore, restriction is appropriate. The requirement is still deemed proper and is therefore is made FINAL. Claims 13-15 are withdrawn from consideration. Claim Rejections - 35 USC § 112 The following is a quotation of 35 U.S.C. 112(b): (b) CONCLUSION.—The specification shall conclude with one or more claims particularly pointing out and distinctly claiming the subject matter which the inventor or a joint inventor regards as the invention. The following is a quotation of 35 U.S.C. 112 (pre-AIA ), second paragraph: The specification shall conclude with one or more claims particularly pointing out and distinctly claiming the subject matter which the applicant regards as his invention. Claims 2 and 12 is rejected under 35 U.S.C. 112(b) or 35 U.S.C. 112 (pre-AIA ), second paragraph, as being indefinite for failing to particularly point out and distinctly claim the subject matter which the inventor or a joint inventor (or for applications subject to pre-AIA 35 U.S.C. 112, the applicant), regards as the invention. Regarding claim 2, since a preamble recited as “The method for producing an alkali salt of bis(fluorosulfonyl)imide”, its dependency of claim 2 is missing. An appropriated correction is required. The phrase "preferably" recited in claim 12 renders the claim indefinite because it is unclear whether the limitations following the phrase are part of the claimed invention. See MPEP § 2173.05(d). An appropriated correction is required. Claim Rejections - 35 USC § 103 In the event the determination of the status of the application as subject to AIA 35 U.S.C. 102 and 103 (or as subject to pre-AIA 35 U.S.C. 102 and 103) is incorrect, any correction of the statutory basis (i.e., changing from AIA to pre-AIA ) for the rejection will not be considered a new ground of rejection if the prior art relied upon, and the rationale supporting the rejection, would be the same under either status. 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 1-9 and 12 are rejected under 35 U.S.C. 103 as being unpatentable over Kim et al. (WO 2020/099527 A, applicants submitted in IDS). Regarding claim 1, Kim et al. teach a method for purifying a lithium bis(fluorosulfonyl)imide comprising via reacting bis(chlorosulfonyl)imide salt with a fluorinating reagent NH4F(HF) (n=1) to produce a crude ammonium bis(fluorosulfonyl)imide NH4+[F-SO2-N-SO2-F]- in ethyl acetate (1st solvent) (the claimed step (a) and (b)) (line 5 on page 4-line 30 on page 5), concentration the resulting crude ammonium salt of bis(fluorosulfonyl)imide to 80-95%wt. (line 30-35 on page 6), crystallization the ammonium salt of bis(fluorosulfonyl)imide in a precipitation solvent such as diether ether (line 18 on page 10) and separating crystallized salt of bis(fluorosulfonyl)imide (line 15-24 on page 8) (the claimed step (c)). Since Kim et al. teach all of the claimed reagents such as bis(chlorosulfonyl)imide salt and 1st solvent of ethyl acetate) and method of making an ammonium salt of bis(fluorosulfonyl)imide, the physical properties of the resulting mixture (i.e., a crude bis(chlorosulfonyl)imide salt dissolving in ethyl acetate) would necessarily follow as set forth in MPEP 2112.01(II).[1] Regarding claim 2, the process taught by Kim et al. further comprising reacting the crude of ammonium bis(fluorosulfonyl)imide salt with lithium salt of LiOH to produce lithium bis(fluorosulfonyl)imide (page 11) as the instant claim (pages 3-11). Regarding claim 3, as discussed above, the crude ammonium bis(fluorosulfonyl)imide salt is 80%wt. as the instant claim (page 6). Regarding claims 4, as discussed above, Kim et al. teach [F-SO2-N-SO2-F]-Li+ (x=Li) as the instant claim ([ (page 11). Regarding claim 5, as discussed above, the process taught by Kim et al. comprises via reacting bis(chlorosulfonyl)imide with fluorinating reagent NH4F(HF) (n=0) to produce a crude ammonium bis(fluorosulfonyl)imide NH4+[F-SO2-N-SO2-F]- in ethyl acetate (page 5). Regarding claims 6-7, as discussed above, Kim et al. teach an amount of 400 g of ethyl methyl carbonate or alternative ethyl acetate (applicant’s 1st solvent) used for producing an amount of 89 g of ammonium bis(fluorosulfonyl)imide. Therefore, a mass ratio is 4.5:1 which is encompassed by the instant claimed ranges (Example 1, page 14). Regarding claim 8, although Kim et al. do not specifically disclose dropwise addition of diethyl ether (2nd solvent) as per applicant claim 8, it is known to one of ordinary skill in the art at the time the invention was filed to dropwise addition the 2nd solvent, the solution should become cloudy. This cloudiness indicates that the 2nd solvent is inducing crystallization. The addition of solvent should be done dropwise until the solution just becomes cloudy. Regarding claim 9, as discussed above, the process taught by Kim et al. comprise diethyl ether as the instant claim (page 10). Regarding claim 12, a s discussed above, the process taught by Kim et al. comprise further reacting crystallized ammonium salt of bis(fluorosulfonyl)imide with lithium salt of LiOH as the instant claim (page 11). Claims 1, 3-4, and 6-12 are rejected under 35 U.S.C. 103 as being unpatentable over Yang et al. (CN 110697668 A, applicants submitted in IDS, Machine-generated (PE2E) English translation is attached). Regarding claim 1, Yang et al. teach a method for purifying Lithium salt of bis(fluorosulfonyl)imide (LiFSI) comprising reacting bis(fluorosulfonyl)imide with lithium sulfate in non-aqueous solvent acetonitrile (applicant’s 1st solvent) to form a crude lithium salt of bis(fluorosulfonyl)imide (the instant claim 1 (a)), as such the crude lithium salt of bis(fluorosulfonyl)imide dissolved in acetonitrile (the instant claim 1 (b)), the resulting crude lithium salt of bis(fluorosulfonyl)imide is purified by crystallization with a poor soluble solvent such as tetrachloroethanes, or alternative propyl ether (the claimed 2nd solvent )([0079]-[0092], Example 1, [0106]). Regarding claim 3, the process of Yang et al comprises filtration of the resulting by-products of Li2SO4 and LiHSO4, concentration the filtrate via evaporating 1st solvent and to produce a thick semi-transparent oil of crude lithium salt of bis(fluorosulfonyl)imide. Since the final pure LiFSI is 97% yield (182.1 g), as such, the weight % of the resulting crude is expected to be about 80-97% as the instant claim (Example 1, [0106]). Regarding claim 4, as discussed above, Yang et al. teach [F-SO2-N-SO2-F]-Li+ (x=Li) as the instant claim ([0004]-[0031]). Regarding claims 6-7, as discussed above, Yang et al. teach a dropwise addition of an amount of 181 g of bis(fluorosulfonyl)imide (1.0 mol) to the solution containing an amount of 300 g of acetonitrile (applicant’s 1st solvent) to form a crude LiFSI. Although Yang et al do not specifically disclose an amount of the crude oily LiFSI after filtration and evaporation, the final pure white power LiFSI is obtained as 182.1 g (about 97% yield). As such, the crude LiFSI is about 182 g. Therefore, a mass ratio is 1.65:1 which is encompassed by the instant claimed ranges (Example 1, [0106]). Regarding claim 8, although Yang et al. do not specifically disclose dropwise addition of propyl ether (2nd solvent) as per applicant claim 8, it is known to one of ordinary skill in the art at the time the invention was filed to dropwise addition the 2nd solvent, the solution should become cloudy. This cloudiness indicates that the 2nd solvent is inducing crystallization. The addition of solvent should be done dropwise until the solution just becomes cloudy. Regarding claim 9, as discussed above, the process taught by Kim et al. comprise propyl ether as the instant claim. Regarding claim 10, as discussed above, Yang et al. teach to use an amount of 800 g of tetrachloroethane (applicant’s 2nd solvent) to produce an amount of 182 g of bis(fluorosulfonyl)imide. Yang et al. teach a poor solubility solvent used for crystallization including tetrachloroethane and propyl ether ([0083). Alternative, a poor solubility solvent of propyl ether can be used instead of tetrachloroethane. Although Yang et al do not specifically disclose an amount of the crude oily LiFSI after filtration and evaporation, the final pure white power LiFSI is obtained as 182.1 g (about 97% yield). As such, the crude LiFSI is about 182 g (Example 1, [0106])-[0113]). Therefore, a mass ratio is 4.4:1 which is encompassed by the instant claimed ranges (Example 1, [0106]-[0113]). Regarding claim 11, the process taught by Yang et al. includes drying after filtration of wet white lithium bis(fluorosulfonyl)imide as the instant claim (Example 1, [0106]). Regarding claim 12, the process taught by Yang et al. lithium bis(fluorosulfonyl)imide as the instant claim (Example 1, [0106]). Conclusion Any inquiry concerning this communication or earlier communications from the examiner should be directed to YUN QIAN whose telephone number is (571)270-5834. The examiner can normally be reached Monday-Thursday 10:00am-4:00pm. Examiner interviews are available via telephone, in-person, and video conferencing using a USPTO supplied web-based collaboration tool. To schedule an interview, applicant is encouraged to use the USPTO Automated Interview Request (AIR) at http://www.uspto.gov/interviewpractice. If attempts to reach the examiner by telephone are unsuccessful, the examiner’s supervisor, Sally A Merkling can be reached at 571-272-6297. The fax phone number for the organization where this application or proceeding is assigned is 571-273-8300. Information regarding the status of published or unpublished applications may be obtained from Patent Center. Unpublished application information in Patent Center is available to registered users. To file and manage patent submissions in Patent Center, visit: https://patentcenter.uspto.gov. Visit https://www.uspto.gov/patents/apply/patent-center for more information about Patent Center and https://www.uspto.gov/patents/docx for information about filing in DOCX format. For additional questions, contact the Electronic Business Center (EBC) at 866-217-9197 (toll-free). If you would like assistance from a USPTO Customer Service Representative, call 800-786-9199 (IN USA OR CANADA) or 571-272-1000. YUN . QIAN Examiner Art Unit 1732 /YUN QIAN/Primary Examiner, Art Unit 1738 [1][1] “Products of identical chemical composition cannot have mutually exclusive properties.” A chemical composition and its properties are inseparable. Therefore, if the prior art teaches the identical chemical structure, the properties applicant discloses and/or claims are necessarily present. In re Spada, 911 F.2d 705, 709, 15 USPQ2d 1655, 1658 (Fed. Cir. 1990).
Read full office action

Prosecution Timeline

Mar 09, 2023
Application Filed
Nov 26, 2025
Non-Final Rejection — §103, §112 (current)

Precedent Cases

Applications granted by this same examiner with similar technology

Patent 12600906
RED-LUMINESCENT PHOSPHOR WITH LONG AFTERGLOW AND FABRICATION METHOD THEREOF
2y 5m to grant Granted Apr 14, 2026
Patent 12595171
Co-production of Hydrogen and Sulfuric Acid by Partial Oxidation of Sulfur
2y 5m to grant Granted Apr 07, 2026
Patent 12592423
PROCESS AND ITS PRODUCTS FOR SPENT LITHIUM-ION BATTERIES TREATMENT
2y 5m to grant Granted Mar 31, 2026
Patent 12589383
Spherical Titanium Silicalite Molecular Sieve Catalyst and Preparation Method Therefor
2y 5m to grant Granted Mar 31, 2026
Patent 12577126
METHOD FOR PRODUCING NICKEL PARTICLES, METHOD FOR PRODUCING NICKEL SULFATE, AND METHOD FOR PRODUCING POSITIVE ELECTRODE ACTIVE MATERIAL FOR SECONDARY BATTERIES
2y 5m to grant Granted Mar 17, 2026
Study what changed to get past this examiner. Based on 5 most recent grants.

AI Strategy Recommendation

Get an AI-powered prosecution strategy using examiner precedents, rejection analysis, and claim mapping.
Powered by AI — typically takes 5-10 seconds

Prosecution Projections

1-2
Expected OA Rounds
54%
Grant Probability
75%
With Interview (+20.3%)
3y 3m
Median Time to Grant
Low
PTA Risk
Based on 1081 resolved cases by this examiner. Grant probability derived from career allow rate.

Sign in with your work email

Enter your email to receive a magic link. No password needed.

Personal email addresses (Gmail, Yahoo, etc.) are not accepted.

Free tier: 3 strategy analyses per month