Electrolyte for inhibiting iron dissolution of high compaction button cell, high compaction button cell

Abstract

The application belongs to the technical field of lithium ion battery electrolyte, and particularly relates to an electrolyte for inhibiting iron dissolution of high-compaction button cell and a high-compaction button cell; based on the total mass of the electrolyte, the electrolyte comprises: an additive, the additive comprises 0.1-0.5wt% ferrocene and 0.5-3wt% tetrabutylammonium hexafluorophosphate; a lithium salt, the content of the lithium salt is 10-15wt%; and the rest is an organic solvent; by setting the ferrocene and tetrabutylammonium hexafluorophosphate as the additive, the application not only solves the surface problem of long constant-voltage charging time, but also solves the essential problem of electrolyte blackening and SEI film thickening caused by iron ion migration, and comprehensively improves the battery performance.

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion battery electrolyte technology, specifically relating to an electrolyte that inhibits iron dissolution in high-voltage button cells and a high-voltage button cell. Background Technology

[0002] Lithium iron phosphate (LiFePO4) plays a crucial role in power batteries and energy storage due to its stable structure, high safety, and low cost. To further improve energy density, the industry commonly employs strategies to increase the compaction density of the cathode. Currently, in coin cell research, the compaction density of high-compact LFP electrodes often reaches 2.6 g / cm³. 3 above.

[0003] However, the following abnormal phenomena frequently occur during the cycling process of the high-voltage LFP button cell: (1) The duration of the constant voltage charging stage is abnormally prolonged, from the normal 8-20 minutes to 30-70 minutes; (2) The charge and discharge specific capacity continues to decay, and the cycle life is significantly shortened; (3) After disassembling the battery, there are black colloidal suspensions on the surface of the electrolyte (the electrolyte itself is colorless and transparent) or the electrolyte is directly contaminated and turns black.

[0004] Therefore, overcoming the degradation of cycle performance caused by the dissolution of iron ions in the electrolyte of high-pressure LFP coin cells is a technical problem that urgently needs to be solved in this field.

[0005] It should be noted that the information disclosed in this background section is only for understanding the background technology of the present application concept, and therefore, the above description is not considered to constitute prior art information. Summary of the Invention

[0006] This disclosure provides at least one electrolyte for suppressing iron dissolution in a high-voltage button cell and a high-voltage button cell.

[0007] In a first aspect, embodiments of this disclosure provide an electrolyte for suppressing iron dissolution in a high-voltage button cell battery. Based on the total mass of the electrolyte, the electrolyte comprises: an additive, the additive comprising 0.1-0.5 wt% ferrocene and 0.5-3 wt% tetrabutylammonium hexafluorophosphate; a lithium salt, the lithium salt comprising 10-15 wt%; and the balance being an organic solvent.

[0008] In one alternative embodiment, the lithium salt comprises any one or more combinations of lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide, and lithium difluorooxalateborate.

[0009] In one optional embodiment, the organic solvent is a carbonate solvent, including any one or more combinations of ethylene carbonate, dimethyl carbonate, ethyl methyl carbonate, and diethyl carbonate.

[0010] In one optional embodiment, the organic solvent is a mixed solvent of ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate, wherein the volume ratio of ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate is 1:1:1.

[0011] Secondly, this disclosure also provides a method for preparing an electrolyte that suppresses iron dissolution from a high-voltage coin cell as described above, comprising the following steps: dissolving a lithium salt in an organic solvent under a protective atmosphere to obtain a solution; adding an additive to the solution and stirring until completely dissolved to obtain an electrolyte that suppresses iron dissolution from a high-voltage coin cell.

[0012] In one optional embodiment, the protective atmosphere contains H2O < 0.01 ppm and O2 < 0.01 ppm.

[0013] Thirdly, embodiments of this disclosure also provide a high-voltage button cell, comprising: a positive electrode, a lithium metal negative electrode, a separator, and an electrolyte as described above to suppress iron dissolution from the high-voltage button cell.

[0014] In one optional embodiment, the positive electrode sheet has a compaction density ≥ 2.60 g / cm³. 3 Lithium iron phosphate.

[0015] Fourthly, this disclosure also provides a method for preparing a high-voltage coin cell battery, comprising the following steps: preparing an electrolyte as described above to suppress iron dissolution in the high-voltage coin cell battery; preparing a positive electrode sheet using high-voltage lithium iron phosphate as the active material; assembling the positive electrode sheet, negative electrode sheet, and separator; injecting the electrolyte to obtain a high-voltage coin cell battery.

[0016] Fifthly, embodiments of this disclosure also provide an electrical device, including the high-voltage button cell battery as described above.

[0017] The beneficial effects of this invention are as follows: the electrolyte for suppressing iron dissolution in high-voltage coin cells, and the high-voltage coin cell itself, by using ferrocene and tetrabutylammonium hexafluorophosphate as additives, utilize the cyclical interaction of ferrous and ferric iron in ferrocene to provide additional charge transfer channels, thereby shortening the constant-voltage charging time; simultaneously, tetrabutylammonium hexafluorophosphate dissociates in the electrolyte into larger tetrabutylammonium cations and hexafluorophosphate ions, wherein the tetrabutylammonium cations adsorb free iron complex anions in the electrolyte through electrostatic interaction, forming ion pairs or weak complexes, thus physically blocking the migration of iron ions; the combined effect of the two additives solves both the apparent problem of long constant-voltage charging time and the fundamental problem of electrolyte blackening and SEI film thickening caused by iron ion migration, thus achieving a comprehensive improvement in battery performance.

[0018] Other features and advantages of the invention will be set forth in the following description, and will be apparent in part from the description, or may be learned by practicing the invention. The objects and other advantages of the invention are realized and obtained through the structures particularly pointed out in the description and the drawings.

[0019] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, preferred embodiments are described below in detail with reference to the accompanying drawings. Attached Figure Description

[0020] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0021] Figure 1 The 0.1C 50-cycle charge-discharge diagram provided in Example 1; Figure 2 This is a 0.1C 50-cycle charge-discharge diagram provided in Example 2; Figure 3 This is a 0.1C 50-cycle charge-discharge diagram provided in Example 3; Figure 4 The 0.1C 50-cycle charge-discharge diagram provided for Comparative Example 1; Figure 5 The 0.1C 50-cycle charge-discharge diagram provided for Comparative Example 2; Figure 6 The 0.1C 50-cycle charge-discharge diagram is provided for Comparative Example 3. Detailed Implementation

[0022] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0023] As used herein, the phrases “in one embodiment,” “according to one embodiment,” “in some embodiments,” etc., generally refer to the fact that a particular feature, structure, or characteristic following the phrase can be included in at least one embodiment of this disclosure. Therefore, a particular feature, structure, or characteristic can be included in more than one embodiment of this disclosure, such that these phrases do not necessarily refer to the same embodiment. As used herein, the terms “example,” “exemplary,” etc., are used to “serve as an example, instance, or illustration.” Any implementation, aspect, or design described herein as “example” or “exemplary” is not necessarily to be construed as preferred or superior to other implementations, aspects, or designs. Rather, the use of the terms “example,” “exemplary,” etc., is intended to present concepts in a specific manner.

[0024] The following are explanations of some terms in this article: Tetrabutylammonium hexafluorophosphate (TBAPF6), tetrabutylammonium cationic TBA + hexafluorophosphate PF6 - Solid electrolyte interphase (SEI) membrane, lithium hexafluorophosphate (LiPF6), lithium bis(fluorosulfonyl)imide (LiFSI), lithium difluorooxalate borate (LiFOB), ethylene carbonate (EC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), lithium iron phosphate (LFP), conductive carbon black (Super P), polyvinylidene fluoride (PVDF), N-methylpyrrolidone (NMP).

[0025] According to the inventor's analysis, the fundamental reason for the presence of black colloidal suspension residue on the electrolyte surface, or for the electrolyte being directly contaminated and turning black, is that under high compaction conditions, LFP secondary particles develop microcracks or even break during the rolling process, exposing fresh surfaces that are not completely covered by the carbon layer. These highly reactive surfaces react with trace amounts of residual moisture and HF in the electrolyte, leading to the deposition of some Fe... 2+ Oxidized to Fe 3+ And it dissolves into the electrolyte. Some of the dissolved iron ions react with trace amounts of F in the electrolyte. - Soluble iron-fluoride complex anions are formed, while the remainder are suspended in the electrolyte as ferric hydroxide or ferric phosphate colloids. The soluble iron-fluoride complex anions are much smaller than the membrane pore size and migrate along with lithium ions through the porous membrane to the negative electrode surface under the influence of the electric field during charging. Insoluble colloidal particles, however, are trapped by the membrane, causing the electrolyte to appear black. The iron-fluoride anions reaching the negative electrode surface are reduced to low-valence iron species, simultaneously catalyzing the reduction and decomposition of the carbonate solvent, leading to an abnormally thickened SEI film, which is the direct cause of the abnormally prolonged constant-voltage charging time.

[0026] Ferrocene compounds have reversible redox properties and are often used as redox additives or charge transfer promoters in electrochemical systems. Tetrabutylammonium hexafluorophosphate contains tetrabutylammonium cations and hexafluorophosphate anions and is often studied or used as an additive or conductive salt component containing quaternary ammonium salt cations and hexafluorophosphate ions in electrolytes or related electrochemical systems.

[0027] The shortcomings of the above solutions are the result of the inventor's practical experience and careful research. Therefore, the discovery process of the above problems and the solutions proposed in this disclosure below should be considered as the inventor's contribution to this disclosure.

[0028] The following detailed description of some embodiments of the present invention is provided in conjunction with the accompanying drawings. Unless otherwise specified, the following embodiments and features can be combined with each other.

[0029] This disclosure provides an electrolyte for suppressing iron dissolution in a high-voltage button cell battery. Based on the total mass of the electrolyte, it includes: an additive comprising 0.1–0.5 wt% ferrocene and 0.5–3 wt% tetrabutylammonium hexafluorophosphate; a lithium salt comprising 10–15 wt%; and the balance being an organic solvent.

[0030] Specifically, ferrocene is an electrochemically reversible redox pair. During the constant-voltage charging phase, when the lithium-ion extraction rate on the surface of LFP particles is limited by solid-phase diffusion, ferrocene molecules can act as electron shuttles in the electrolyte. Although the molecular diameter of ferrocene is much smaller than the pore size of the separator, due to electrochemical behavior, ferrocene is reduced to Fe within microseconds after being oxidized on the positive electrode surface. It does not have enough time to diffuse to the other side of the separator, therefore it can only act on the positive electrode side and cannot penetrate the separator or act on the negative electrode. The Fe in the ferrocene molecule... 2+ It is oxidized to Fe on the positive electrode surface. 3+ Ferrocene ions are generated; subsequently, they first lose electrons at the positive electrode surface and then gain electrons at the conductive network, Fe 3+ It was reduced back to Fe 2+ The ferrocene molecules revert to neutral states. This process provides additional charge transfer pathways, significantly shortening the constant-voltage charging time. Ferrocene is not consumed in this process; it only acts as a catalyst.

[0031] Specifically, tetrabutylammonium hexafluorophosphate dissociates into larger TBA in the electrolyte. + and PF6 - TBA + Carrying a positive charge, it can adsorb free [FeF6] in the electrolyte through electrostatic interactions. 3- [FeCl4]- Negatively charged iron-containing anions form ion pairs or weak complexes. This physical blocking effect effectively reduces the migration rate of iron-containing anions to the negative electrode under the drive of the electric field, thereby inhibiting the reduction deposition of iron ions on the negative electrode surface and their catalytic damage to the SEI film. The electrolyte thus remains clear, and black colloids no longer appear.

[0032] Specifically, the content of tetrabutylammonium hexafluorophosphate is 0.5–3 wt% of the total mass of the electrolyte. It is not used as the main electrolyte salt, but as an inhibitor of iron ion migration. In this invention, tetrabutylammonium hexafluorophosphate serves as an additive that meets three requirements: large-volume cation, weakly coordinated anion, and electrochemical stability. Among these requirements, the large-volume cation must have sufficient steric hindrance to block the migration path of iron ions. Replacing it with a smaller quaternary ammonium salt cation such as tetraethylammonium would affect this effect. The weakly coordinated anion requirement is that the additive cannot form stable complexes with divalent / trivalent iron ions to avoid the migration behavior of iron ions in the electrolyte or the introduction of impurities. The electrochemical stability requirement is that the additive does not decompose within the operating voltage and does not undergo side reactions with lithium salts / organic solvents.

[0033] In some embodiments, specifically, the lithium salt includes any one or more combinations of lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide, and lithium difluorooxalateborate.

[0034] In some embodiments, specifically, the organic solvent is a carbonate solvent, including any one or more combinations of ethylene carbonate, dimethyl carbonate, methyl ethyl carbonate, and diethyl carbonate.

[0035] In some embodiments, specifically, the organic solvent is a mixed solvent of ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate, wherein the volume ratio of ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate is 1:1:1.

[0036] This disclosure also provides a method for preparing an electrolyte that suppresses iron dissolution from a high-voltage button cell as described above, comprising the following steps: dissolving a lithium salt in an organic solvent under a protective atmosphere to obtain a solution; adding an additive to the solution and stirring until completely dissolved to obtain an electrolyte that suppresses iron dissolution from a high-voltage button cell.

[0037] In some embodiments, specifically, in the protective atmosphere, H2O < 0.01 ppm and O2 < 0.01 ppm.

[0038] This disclosure also provides a high-voltage button cell, comprising: a positive electrode, a lithium metal negative electrode, a separator, and an electrolyte as described above to suppress iron dissolution from the high-voltage button cell.

[0039] In some embodiments, specifically, the positive electrode sheet has a compaction density ≥ 2.60 g / cm³. 3 Lithium iron phosphate.

[0040] This disclosure also provides a method for preparing a high-voltage coin cell, comprising the following steps: preparing an electrolyte as described above to suppress iron dissolution in the high-voltage coin cell; preparing a positive electrode sheet using high-voltage lithium iron phosphate as the active material; assembling the positive electrode sheet, negative electrode sheet, and separator; injecting the electrolyte to obtain a high-voltage coin cell.

[0041] This disclosure also provides an electrical device, including the high-voltage button cell battery as described above; the electrical device is any portable device that uses a button cell battery and has requirements for charging speed and cycle life, such as a Bluetooth headset, smartwatch, electronic tag, remote control, small medical device or Internet of Things sensing device.

[0042] Example 1: An electrolyte and a high-voltage button cell Electrolyte preparation method: In an argon-atmospheric glove box (H2O < 0.01 ppm, O2 < 0.01 ppm), based on the total mass of the electrolyte, 12% by mass of LiPF6 solid powder was dissolved in a mixed solvent of EC / DMC / EMC (volume ratio 1:1:1) to prepare a 1 mol / L solution. Then, based on the total mass of the electrolyte, 0.3% by mass of ferrocene (AR grade 99%) and 2% by mass of tetrabutylammonium hexafluorophosphate were added sequentially, and stirred until completely dissolved to obtain the electrolyte.

[0043] Preparation of positive electrode: With a compaction density of 2.60 g / cm³ 3 High-pressure lithium iron phosphate (LFP) was used as the active material. LFP, Super P, and PVDF were mixed in a mass ratio of 92:3:5, and a slurry was prepared using NMP as a solvent. The slurry was then coated onto aluminum foil. After drying and rolling, the foil was cut into positive electrode sheets with a diameter of 12 mm.

[0044] Assembly of button cells: In the glove box, a lithium metal sheet is used as the negative electrode, Celgard 2500 is used as the separator, and it is assembled with the positive electrode. The above-mentioned electrolyte is injected to assemble a 2430 coin cell.

[0045] Example 2: An electrolyte and a high-voltage button cell Electrolyte preparation method: In an argon-atmospheric glove box (H2O < 0.01 ppm, O2 < 0.01 ppm), based on the total mass of the electrolyte, 12% (w / w) of LiPF6 solid powder was dissolved in a mixed solvent of EC / DMC / EMC (volume ratio 1:1:1) to prepare a 1 mol / L solution. Then, based on the total mass of the electrolyte, 0.1% (w / w) of ferrocene (AR grade 99%) and 1% (w / w) of tetrabutylammonium hexafluorophosphate were added sequentially, and the mixture was stirred until completely dissolved to obtain the electrolyte.

[0046] Preparation of positive electrode: With a compaction density of 2.60 g / cm³ 3 High-pressure lithium iron phosphate (LFP) was used as the active material. LFP, Super P, and PVDF were mixed in a mass ratio of 92:3:5, and a slurry was prepared using NMP as a solvent. The slurry was then coated onto aluminum foil. After drying and rolling, the foil was cut into positive electrode sheets with a diameter of 12 mm.

[0047] Assembly of button cells: In the glove box, a lithium metal sheet is used as the negative electrode, Celgard 2500 is used as the separator, and it is assembled with the positive electrode. The above-mentioned electrolyte is injected to assemble a 2430 coin cell.

[0048] Example 3: An electrolyte and a high-voltage button cell Electrolyte preparation method: In an argon-atmospheric glove box (H2O < 0.01 ppm, O2 < 0.01 ppm), based on the total mass of the electrolyte, 12% (w / w) of LiPF6 solid powder was dissolved in a mixed solvent of EC / DMC / EMC (volume ratio 1:1:1) to prepare a 1 mol / L solution. Then, based on the total mass of the electrolyte, 0.5% (w / w) of ferrocene (AR grade 99%) and 3% (w / w) of tetrabutylammonium hexafluorophosphate were added sequentially, and the mixture was stirred until completely dissolved to obtain the electrolyte.

[0049] Preparation of positive electrode: With a compaction density of 2.60 g / cm³ 3 High-pressure lithium iron phosphate (LFP) was used as the active material. LFP, Super P, and PVDF were mixed in a mass ratio of 92:3:5, and a slurry was prepared using NMP as a solvent. The slurry was then coated onto aluminum foil. After drying and rolling, the foil was cut into positive electrode sheets with a diameter of 12 mm.

[0050] Assembly of button cells: In the glove box, a lithium metal sheet is used as the negative electrode, Celgard 2500 is used as the separator, and it is assembled with the positive electrode. The above-mentioned electrolyte is injected to assemble a 2430 coin cell.

[0051] Comparative Example 1: An electrolyte and a button cell Electrolyte: A standard electrolyte of model FB097 is used.

[0052] Preparation of positive electrode: With a compaction density of 2.60 g / cm³ 3 High-pressure lithium iron phosphate (LFP) was used as the active material. LFP, Super P, and PVDF were mixed in a mass ratio of 92:3:5, and a slurry was prepared using NMP as a solvent. The slurry was then coated onto aluminum foil. After drying and rolling, the foil was cut into positive electrode sheets with a diameter of 12 mm.

[0053] Assembly of button cells: In the glove box, a lithium metal sheet is used as the negative electrode, Celgard 2500 is used as the separator, and it is assembled with the positive electrode. The above-mentioned electrolyte is injected to assemble a 2430 coin cell.

[0054] Comparative Example 2: An electrolyte and a button cell Electrolyte preparation method: In an argon-atmospheric glove box (H2O < 0.01 ppm, O2 < 0.01 ppm), based on the total mass of the electrolyte, 12% (w / w) of LiPF6 solid powder was dissolved in a mixed solvent of EC / DMC / EMC (volume ratio 1:1:1) to prepare a 1 mol / L solution. Then, based on the total mass of the electrolyte, 0.3% (w / w) of ferrocene (AR grade 99%) was added and stirred until completely dissolved to obtain the electrolyte.

[0055] Preparation of positive electrode: With a compaction density of 2.60 g / cm³ 3 High-pressure lithium iron phosphate (LFP) was used as the active material. LFP, Super P, and PVDF were mixed in a mass ratio of 92:3:5, and a slurry was prepared using NMP as a solvent. The slurry was then coated onto aluminum foil. After drying and rolling, the foil was cut into positive electrode sheets with a diameter of 12 mm.

[0056] Assembly of button cells: In the glove box, a lithium metal sheet is used as the negative electrode, Celgard 2500 is used as the separator, and it is assembled with the positive electrode. The above-mentioned electrolyte is injected to assemble a 2430 coin cell.

[0057] Comparative Example 3: An electrolyte and a button cell Electrolyte preparation method: In an argon-atmospheric glove box (H2O < 0.01 ppm, O2 < 0.01 ppm), based on the total mass of the electrolyte, 12% by mass of LiPF6 solid powder was dissolved in a mixed solvent of EC / DMC / EMC (volume ratio 1:1:1) to prepare a 1 mol / L solution. Then, based on the total mass of the electrolyte, 2% by mass of tetrabutylammonium hexafluorophosphate was added and stirred until completely dissolved to obtain the electrolyte.

[0058] Preparation of positive electrode: With a compaction density of 2.60 g / cm³ 3 High-pressure lithium iron phosphate (LFP) was used as the active material. LFP, Super P, and PVDF were mixed in a mass ratio of 92:3:5, and a slurry was prepared using NMP as a solvent. The slurry was then coated onto aluminum foil. After drying and rolling, the foil was cut into positive electrode sheets with a diameter of 12 mm.

[0059] Assembly of button cells: In the glove box, a lithium metal sheet is used as the negative electrode, Celgard 2500 is used as the separator, and it is assembled with the positive electrode. The above-mentioned electrolyte is injected to assemble a 2430 coin cell.

[0060] Specifically, constant current and constant voltage charge and discharge tests were conducted at 25°C and a rate of 0.1C (charging cutoff voltage 3.92 V, discharging cutoff voltage 1.98 V). The test results of Examples 1-3 and Comparative Examples 1-3 are shown in Table 1 below.

[0061] Table 1. Charge-discharge cycle, efficiency, and constant voltage duration for 50 cycles under different conditions at 0.1C.

[0062] Please see Figure 1 , Figure 1 This is a 0.1C 50-cycle charge-discharge diagram provided in Example 1. Figure 1 The charging and discharging platform is flat and long, the charging and discharging voltage difference is within 0.05V, the electrode reaction kinetics are excellent, and the reversible capacity is high. After 50 cycles, the battery in Example 1 was disassembled and the electrolyte was clear and transparent with no visible sediment, which is the preferred example.

[0063] Please see Figure 2 , Figure 2 This is a 0.1C 50-cycle charge-discharge diagram provided in Example 2. Figure 2The curves in Example 2 show that its platform stability, polarization degree, and reversible capacity are at the same level as Example 1. In Example 2, the amount of ferrocene added was adjusted to 0.1%, and the amount of TBAPF6 added was adjusted to 1%. At the 50th cycle, the constant voltage charging time was 15 minutes, and the efficiency was 96.69%. After 50 cycles, the battery was disassembled, and the electrolyte was clear and transparent with no visible sediment. The performance of Example 2 is slightly lower than that of Example 1, but considering the lower total additive concentration and lower cost, it still has practical value.

[0064] Please see Figure 3 , Figure 3 This is a 0.1C 50-cycle charge-discharge diagram provided in Example 3. Figure 3 The curve surface in Example 1 continues the advantages of low polarization, high capacity and stable platform. In Example 3, the amount of ferrocene added was adjusted to 0.5% and the amount of TBAPF6 added was adjusted to 3%. The constant voltage charging time was 12 minutes at the 50th cycle and the efficiency was 97.98%. After 50 cycles, the battery was disassembled and the electrolyte was clear and transparent with no visible sediment.

[0065] Please see Figure 4 , Figure 4 The 0.1C 50-cycle charge-discharge diagram provided for Comparative Example 1 Figure 4 The first charge in the first example exhibits a significant low-voltage activation process, with a large amount of capacity consumed in the non-effective plateau region, and the reversible capacity is also significantly lower than that in Examples 1-3. In Comparative Example 1, the electrolyte of the present invention was replaced with a conventional electrolyte, and the constant voltage charging time for 50 cycles was 68 minutes. The electrolyte was black, and the efficiency was 72.73%. Moreover, the battery experienced voltage drops, the specific capacity was artificially high, the discharge was incomplete, the conventional lithium-ion electrolyte could not remove the dissolved iron ions, the constant voltage time was abnormal, and the cycle efficiency was poor.

[0066] Please see Figure 5 , Figure 5 The 0.1C 50-cycle charge-discharge diagram provided for Comparative Example 2 is as follows. Figure 5 Although the extreme low-voltage activation problem of Comparative Example 1 was not present, the charge / discharge plateau was tilted and the polarization was excessive, while the reversible capacity was also lower than that of Examples 1-3. Comparative Example 2 only added 0.3% ferrocene, the same as in Example 1, without adding TBAPF6. The constant voltage charging time at the 50th cycle was 36 minutes, the electrolyte turned light gray, the efficiency was 89.41%, and a small amount of iron was detected by ICP on the negative electrode surface. This indicates that although ferrocene can accelerate charging, it cannot prevent iron ion migration, and the fundamental problems of electrolyte contamination and SEI thickening remain unresolved.

[0067] Please see Figure 6 , Figure 6 The 0.1C 50-cycle charge-discharge diagram provided for Comparative Example 3 is as follows. Figure 6The same issues as Example 1 exist: short platform length, large capacity, and low reversible capacity. Comparative Example 3, with the same 2% TBAPF6 as Example 1 but without ferrocene, showed a constant voltage charging time of 41 minutes at the 50th cycle, a clear electrolyte, an efficiency of 90.55%, and no iron detected on the negative electrode surface. This indicates that TBAPF6 effectively inhibits iron ion migration but has no effect on improving charging kinetics.

[0068] As can be seen from Comparative Examples 2 and 3, if ferrocene or tetrabutylammonium hexafluorophosphate is introduced into the electrolyte alone, each may usually exhibit certain electrochemical or ionic effects. However, it cannot be expected that the combination of the two can form a synergistic improvement in high-voltage coin-type lithium iron phosphate batteries. That is, on the one hand, ferrocene is used to promote charge transfer and alleviate tailing in the constant voltage stage, and on the other hand, the tetrabutylammonium cation-related effect in tetrabutylammonium hexafluorophosphate is used to suppress iron complexation / iron migration problems, thereby maintaining electrolyte clarity and improving cycle performance.

[0069] Furthermore, TBA + Cations can adsorb free ferric fluoride complex anions / iron-related negatively charged species in the electrolyte through electrostatic interactions, forming ion pairs or weak complexes. This reduces the migration of iron-related species to the negative electrode side through physical binding / migration inhibition. Suppressing the migration of iron-related species reduces their participation in side reactions at the negative electrode interface and the resulting abnormal SEI growth / thickness and increased interfacial impedance. This also helps to improve the problem of prolonged constant-voltage charging time caused by increased interfacial polarization. Ferrocene improves the electrochemical polarization process through its reversible redox / charge transfer promoting effect. The combined effect of these two additives improves constant-voltage charging performance from the perspective of charge transfer and addresses the fundamental problems by inhibiting the migration of iron ions / ferric fluoride complex anions and the resulting electrolyte blackening and abnormal SEI thickening at the negative electrode interface, thus achieving a comprehensive improvement in battery performance.

[0070] It should be noted that TBAPF6, as a component that inhibits iron dissolution / iron-related species migration, mainly achieves its effect by reducing the negative electrode interface side reactions and abnormal SEI thickening / resistance increase caused by iron-related species migration. In Comparative Examples 2 and 3 of this case, its use alone did not achieve the same comprehensive effect as when it was compounded with ferrocene. The significant improvement in constant voltage charging time depends on the combined effect of ferrocene and TBAPF6.

[0071] In summary, this high-voltage coin cell electrolyte, which suppresses iron dissolution, and the high-voltage coin cell itself utilize ferrocene and tetrabutylammonium hexafluorophosphate as additives. The cyclical interaction of ferrous and ferric iron in the ferrocene provides additional charge transfer channels, thus shortening the constant-voltage charging time. Simultaneously, the tetrabutylammonium hexafluorophosphate dissociates in the electrolyte into larger tetrabutylammonium cations and hexafluorophosphate ions. The tetrabutylammonium cations adsorb free iron complex anions in the electrolyte through electrostatic interactions, forming ion pairs or weak complexes, thus physically blocking the migration of iron ions. The combined effect of these two additives solves both the apparent problem of long constant-voltage charging time and the fundamental problem of electrolyte blackening and SEI film thickening caused by iron ion migration, achieving a comprehensive improvement in battery performance.

[0072] Based on the above-described preferred embodiments of the present invention, and through the foregoing description, those skilled in the art can make various changes and modifications without departing from the inventive concept. The technical scope of this invention is not limited to the contents of the specification, but must be determined according to the scope of the claims.

Claims

1. An electrolyte for suppressing iron dissolution in high-voltage button cells, characterized in that, Based on the total mass of the electrolyte, it includes: The additives include ferrocene at a content of 0.1 to 0.5 wt% and tetrabutylammonium hexafluorophosphate at a content of 0.5 to 3 wt%. Lithium salt, wherein the lithium salt content is 10-15 wt%; The remainder is organic solvent.

2. The electrolyte for suppressing iron dissolution in high-voltage button batteries as described in claim 1, characterized in that, The lithium salt includes any one or a combination of lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide, and lithium difluorooxalate borate.

3. The electrolyte for suppressing iron dissolution in high-voltage button cells as described in claim 1, characterized in that, The organic solvent is a carbonate solvent, including any one or more combinations of ethylene carbonate, dimethyl carbonate, methyl ethyl carbonate, and diethyl carbonate.

4. The electrolyte for suppressing iron dissolution in high-voltage button batteries as described in claim 3, characterized in that, The organic solvent is a mixed solvent of ethylene carbonate, dimethyl carbonate and ethyl methyl carbonate, wherein the volume ratio of ethylene carbonate, dimethyl carbonate and ethyl methyl carbonate is 1:1:

1.

5. A method for preparing an electrolyte for suppressing iron dissolution in a high-voltage button cell as described in any one of claims 1-4, characterized in that, Includes the following steps: Under a protective atmosphere, lithium salt is dissolved in an organic solvent to prepare a solution; Add the additive to the solution and stir until completely dissolved to obtain the electrolyte.

6. The method for preparing the electrolyte for suppressing iron dissolution in a high-voltage button cell as described in claim 5, characterized in that, In the protective atmosphere, H2O < 0.01 ppm and O2 < 0.01 ppm.

7. A high-voltage button cell battery, characterized in that, include: Positive electrode, lithium metal negative electrode, separator, and electrolyte as described in any one of claims 1-4 for suppressing iron dissolution in a high-voltage coin cell.

8. The high-voltage button cell battery as described in claim 7, characterized in that, The positive electrode sheet has a compaction density ≥ 2.60 g / cm³. 3 Lithium iron phosphate.

9. A method for preparing a high-voltage button cell, characterized in that, Includes the following steps: Configure the electrolyte as described in any one of claims 1-4 to suppress iron dissolution in high-voltage coin cells; With a compaction density ≥2.60 g / cm³ 3 Lithium iron phosphate was used as the active material to prepare the positive electrode sheet; The positive electrode, negative electrode, and separator are assembled, and electrolyte is injected to obtain a high-voltage button cell.

10. An electrical appliance, characterized in that, Including the high-voltage button cell as described in claim 7 or 8.

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