Electrolyte suitable for battery lithium supplement system, liquid injection method of electrolyte and lithium ion battery
By using oxygen radicals containing boron atoms, sulfate groups and sulfonic acid groups in the lithium-ion battery supplement system to capture the multifunctional additive electrolyte solution, the problem of decomposition of LFO lithium-enhancing agents to produce oxygen and oxygen radicals is solved. It improves the high-temperature performance of the battery and the stability of the SEI film, avoids the increase in impedance, and achieves the improvement of lithium ion transmission efficiency and compensation of active lithium loss.
Patent Information
- Application Number
- CN202411589195.8
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2024-11-08
- Publication Date
- 2024-12-31
AI Technical Summary
In the existing lithium-ion battery lithium supplement system, LFO lithium supplement agent produces oxygen and oxygen free radicals during the decomposition process, resulting in side reactions of electrolytes and increasing impedance and capacity attenuation. The existing solutions include using LNO instead and introducing oxygen free radicals. There are problems such as capturing additives or reducing the decomposition of the current, such as low efficiency, high cost, or deterioration of performance.
An electrolyte is adopted, including one injection of electrolyte and two injections of electrolyte, one injection of film-forming additives are added to the electrolyte, and two injections of the electrolyte are added to the electrolyte with boron atoms, sulfate groups and sulfonic acid groups to capture oxygen radicals. Multifunctional additives are carried out after high-temperature aging through secondary injection to ensure that the additives have sufficient content to capture oxygen radicals in the later cycle and protect battery performance.
Effectively reduce the risk of oxygen radicals combined with electrolyte solvent to form intermediates, reduce gas production and impedance increase, improve the high-temperature performance of the battery and the mechanical stability of the SEI film, avoiding the problem of increasing impedance introduced by conventional additives, and at the same time Provides additional lithium ions to compensate for active lithium losses.
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Abstract
Description
Technical Field
[0001] The present invention relates to the technical field of batteries, and in particular to an electrolyte suitable for a battery lithium supplementation system and an electrolyte injection method thereof, and a lithium ion battery. Background Art
[0002] The capacity decay problem during the cycle of lithium-ion batteries is the key to affecting the service life of batteries. Generally, the capacity decay of lithium-ion batteries can be roughly divided into several main factors: capacity polarization loss, loss of positive and negative electrode active materials, and loss of active lithium. Among them, within the range of battery life (capacity decay to 80% of the initial capacity), the most important decay factor is the loss of active lithium. In the entire life cycle of the battery, a large amount of active lithium is consumed in the formation stage to participate in the SEI film formation reaction, and this part of the active lithium loss accounts for a large proportion, so lithium replenishment technology has been widely studied. Positive electrode lithium replenishment has become the most mainstream lithium replenishment method at present because of its relatively simple process and low introduction cost. Common positive electrode lithium replenishers are lithium ferrite (LFO), lithium nickel oxide (LNO), lithium peroxide (LO), etc. Among them, LFO has the largest specific capacity (867mAh / g) and the highest lithium replenishment efficiency, but it will produce a large amount of oxygen and oxygen free radicals during the decomposition process. The oxygen free radicals will form intermediates with the electrolyte solvent and produce reducing gas at the negative electrode. In the current process flow of lithium replenishment system, negative pressure exhaust is performed during formation to extract the gas generated during formation. However, the residual lithium replenisher after formation will continue to decompose during the subsequent cycle storage process, generating oxygen and oxygen free radicals, causing side reactions in the electrolyte, which in turn causes gas production, impedance increase, capacity decay and even failure.
[0003] At present, the common methods to solve the gas production problem of LFO include: using LNO to replace or partially replace LFO, introducing oxygen free radical capture additives, reducing the formation current to allow the lithium supplement to be fully decomposed, introducing new solvents to replace the easily oxidatively decomposed solvent ethylene carbonate (EC), and coating and modifying LFO.
[0004] (1) The lithium replenishment efficiency of using LNO instead of LFO is low because the lithium replenishment capacity of LNO (400 mAh / g) is much smaller than that of LFO;
[0005] (2) Common oxygen free radical capture additives include: phosphites, nitroxide free radicals, etc. The introduction of these substances will increase the impedance of the electrolyte and affect the electrochemical performance;
[0006] (3) Although reducing the formation current can make the lithium supplement more fully participate in the reaction and avoid decomposition and gas production during the later cycle storage, this method will greatly prolong the production time, reduce production efficiency, and increase production costs;
[0007] (4) Introducing new solvents to replace the easily oxidized solvent ethylene carbonate EC will also deteriorate battery performance. Although this solvent is more stable than ethylene carbonate EC, it usually cannot reach the dielectric constant of ethylene carbonate EC. Replacing ethylene carbonate EC will affect the conductivity of the electrolyte, resulting in poor film quality, large battery impedance, and deterioration of charge and discharge performance.
[0008] (5) Coating and modifying LFO will also greatly increase the production cost of lithium supplements.
[0009] How to solve the negative effects caused by gas production of lithium supplements without affecting battery performance and increasing raw material / production costs is a difficult problem that needs to be solved.
[0010] In view of this, the present invention is proposed. Summary of the invention
[0011] The object of the present invention is to provide an electrolyte solution suitable for a battery lithium supplementation system and a method for injecting the electrolyte solution and a lithium ion battery.
[0012] The present invention is achieved in that:
[0013] In a first aspect, the present invention provides an electrolyte suitable for a battery lithium replenishment system, comprising a first injection electrolyte and a second injection electrolyte, wherein the first injection electrolyte and the second injection electrolyte both comprise a carbonate solvent and a lithium salt, the first injection electrolyte further comprises a film-forming additive, and the second injection electrolyte further comprises a multifunctional additive for capturing oxygen free radicals, wherein the multifunctional additive for capturing oxygen free radicals is a cyclic ester lithium salt compound, wherein the cyclic ester lithium salt compound contains a boron atom and also contains at least one of a sulfate group and a sulfonic acid group.
[0014] In an optional embodiment, the mass percentage of the first electrolyte injection to the electrolyte suitable for the battery lithium replenishment system is 85-95%, and the mass percentage of the second electrolyte injection to the electrolyte suitable for the battery lithium replenishment system is 5-15% respectively;
[0015] Preferably, the amount of the oxygen free radical capture multifunctional additive added is 4-6% of the mass of the second injection electrolyte;
[0016] Preferably, the structural formula of the cyclic ester lithium salt includes At least one of, wherein R1, R2 and R3 are all saturated or unsaturated alkyl groups.
[0017] In an optional embodiment, the 5-trimethylborate lithium-1,3,2-dioxathiazole-2,2-dioxide;
[0018] Preferably, the preparation method of 5-trimethylborate lithium-1,3,2-dioxathiacyclohexane-2,2-dioxide comprises mixing triethylamine, 5-chloro-2,2-dioxo-1,3,2-dioxathiacyclohexane and a first solvent to form a reaction system, installing a condensation reflux tube, adding a bistriphenylphosphine palladium dichloride catalyst to the reaction system, dissolving trimethyl borate and lithium hydroxide in a second solvent, adding the solvent to the reaction system, heating at 60-70° C., condensing and refluxing for 10-20 hours, cooling to 20-30° C., evaporating and concentrating the solution, and precipitating with ether to obtain a purified product;
[0019] Preferably, the volume mass ratio of the triethylamine, the 5-chloro-2,2-dioxo-1,3,2-dioxathiazole and the first solvent is 13-17 ml: 2-3 g: 10-14 ml;
[0020] Preferably, the mass volume ratio of the trimethyl borate, the lithium hydroxide and the second solvent is 1.5-2 g: 0.3-0.7 g: 6-10 ml;
[0021] Preferably, the first solvent and the second solvent are both tetrahydrofuran.
[0022] In an optional embodiment, the The preparation method comprises: adding methanesulfonic acid, boric acid, lithium borate and toluene solvent into a flask purged with nitrogen, installing a condenser reflux tube, stirring evenly, heating to 90-110° C., condensing and reflux for 6 hours, cooling to 20-30° C., filtering the reaction solution to separate the solid product, washing the product with acetonitrile and drying it to obtain the final product;
[0023] Preferably, the mass ratio of the methanesulfonic acid, the boric acid, the lithium borate and the toluene solvent is 1.4-1.6:1.4-1.6:0.5-0.7:9-11.
[0024] In an optional embodiment, the amount of the film-forming additive added is 2-3% of the mass of the electrolyte solution;
[0025] Preferably, the film-forming additive includes at least one of vinylene carbonate, fluoroethylene carbonate, tris(trimethylsilyl)phosphate and tris(trimethylsilyl)borate.
[0026] In an optional embodiment, the concentration of the lithium salt in the first electrolyte and the second electrolyte is 0.8-1.2 mol / L;
[0027] Preferably, the lithium salt includes at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethylsulfonyl)imide, lithium perchlorate, lithium difluorooxalatoborate, lithium difluorobis(oxalatophosphate), lithium difluorophosphate and lithium dioxalatoborate.
[0028] In an optional embodiment, the carbonate solvent includes at least two of ethylene carbonate, propylene carbonate, diethyl carbonate, dimethyl carbonate and ethyl methyl carbonate;
[0029] Preferably, the carbonate solvent comprises, by volume percentage, 20-40% ethylene carbonate, 20-40% ethyl methyl carbonate and 30-50% dimethyl carbonate.
[0030] In a second aspect, the present invention provides a method for injecting an electrolyte suitable for a battery lithium replenishment system as described in any of the aforementioned embodiments, wherein the first injection of electrolyte is injected into a lithium replenishment system soft-pack battery, and then the lithium replenishment system soft-pack battery is subjected to formation, primary exhaust, high-temperature aging and secondary exhaust, and then the second injection of electrolyte is injected.
[0031] In an optional embodiment, the total amount of the first electrolyte injection and the second electrolyte injection is 3.5-4.5 g / Ah;
[0032] And / or, the positive electrode material of the lithium supplement system soft-pack battery includes lithium iron phosphate, ternary material, lithium cobalt oxide or lithium manganese oxide, and the negative electrode material includes graphite, silicon carbon or silicon oxygen.
[0033] In a third aspect, the present invention provides a lithium-ion battery, which is replenished with lithium using the electrolyte injection method applicable to the battery lithium replenishment system as described in the above embodiment.
[0034] The present invention has the following beneficial effects:
[0035] The electrolyte suitable for the battery lithium supplement system provided by the present invention is provided with one injection of electrolyte and two injections of electrolyte, and a film-forming additive is introduced into one injection of electrolyte, and a multifunctional additive for capturing oxygen free radicals containing boron atoms, sulfate groups and / or sulfonic acid groups is introduced into the two injections of electrolyte. Among them, the boron atom has an empty p orbital and is relatively electrophilic, which can capture the oxygen free radicals generated by the decomposition of the lithium supplement agent, avoid it from forming intermediates with the electrolyte solvent, and generate reducing gas at the negative electrode, causing further side reactions. The additive can also participate in the repair of the SEI film in the later stages of circulation and storage, and can form a film at both the positive and negative electrodes, protect the positive and negative electrodes, and reduce the probability of the solvent and oxygen free radicals being oxidized and reduced to produce gas. The electrolyte avoids the problem of increased impedance introduced by conventional additives, and the multifunctional additive is a lithium salt additive. After introduction, the electrolyte is more conducive to lithium ion transmission and can provide additional lithium ions to make up for a certain loss of active lithium. The sulfuric acid / sulfonic acid groups in the structure participate in the film formation to form a SEI film containing S, which helps to reduce impedance, improve the high temperature performance of the battery cell, and enhance the mechanical stability of the SEI film. In addition, the electrolyte adopts a secondary injection method, and the secondary injection step is placed after high temperature aging. The lithium supplement will decompose and produce a large amount of oxygen in the formation stage. If the oxygen free radical capture additive is directly added during the injection, the additive will be consumed during the formation and will not play a protective role in the later stage. There have been reports of two injections before, in which TMP or nitroxide free radical-type free radical capture additives are added after formation and then subjected to high temperature aging. However, in the high temperature aging stage, the reaction of the incompletely formed additive will continue, consuming the free radical capture additive prematurely and weakening its function. Therefore, the present invention adopts a scheme of performing two injections after high temperature aging and exhaust. After aging, the film formation reaction has ended and a stable SEI film has been formed. At this time, the addition of free radical capture additives can ensure that the additive has enough content in the later cycle for continuous consumption and absorbs the oxygen free radicals generated in the later period. DETAILED DESCRIPTION
[0036] In order to make the purpose, technical scheme and advantages of the embodiments of the present invention clearer, the technical scheme in the embodiments of the present invention will be described clearly and completely below. If the specific conditions are not specified in the embodiments, they are carried out according to conventional conditions or conditions recommended by the manufacturer. If the manufacturer of the reagents or instruments used is not specified, they are all conventional products that can be purchased commercially.
[0037] The invention provides an electrolyte suitable for a battery lithium supplementation system, comprising a first-shot electrolyte and a second-shot electrolyte, wherein both the first-shot electrolyte and the second-shot electrolyte comprise a carbonate solvent and a lithium salt, the first-shot electrolyte further comprises a film-forming additive, and the second-shot electrolyte further comprises a multifunctional additive for capturing oxygen free radicals, wherein the multifunctional additive for capturing oxygen free radicals is a cyclic ester lithium salt compound, wherein the cyclic ester lithium salt compound contains a boron atom and also contains at least one of a sulfate group and a sulfonic acid group.
[0038] In the present invention, the electrolyte is composed of a carbonate solvent, a lithium salt, a film-forming additive, and an oxygen free radical capture multifunctional additive. The carbonate solvent is a carbonate solvent commonly used in lithium-ion batteries, and the lithium salt is a commonly used lithium salt, which ensures that the basic physical parameters of the electrolyte, such as viscosity, conductivity, density, etc., are within a normal range, and there is no need to reduce the EC content. The introduction of a new solvent to replace the EC solvent will not affect the performance. In the present invention, by setting up one injection of electrolyte and two injections of electrolyte, and introducing a film-forming additive into one injection of electrolyte, and introducing an oxygen free radical capture multifunctional additive into the two injections of electrolyte, wherein the oxygen free radical capture multifunctional additive contains a boron atom and also contains at least one of a sulfuric acid group and a sulfonic acid group. The boron atom has an empty p orbital and is relatively electrophilic, and can capture the oxygen free radicals generated by the decomposition of the lithium supplement, preventing it from forming an intermediate with the electrolyte solvent, and generating reducing gas at the negative electrode, triggering further side reactions. This multifunctional additive is a lithium salt additive. After its introduction, the electrolyte is more conducive to lithium ion transmission and can provide additional lithium ions to compensate for a certain loss of active lithium. The sulfate group and / or sulfonic acid group in the structure participates in the film formation to form a S-containing SEI film, which helps to reduce impedance and improve the high-temperature performance of the battery cell. The additive can form a film at the negative electrode / positive electrode at the same time, protecting the positive electrode from oxygen dissolution and solvent oxidation, and protecting the negative electrode from oxygen free radicals and solvent intermediates from reduction.
[0039] Specifically, the mass percentage of the first injection electrolyte to the electrolyte suitable for the battery lithium replenishing system is 85-95%, and the mass percentage of the second injection electrolyte to the electrolyte suitable for the battery lithium replenishing system is 5-15%.
[0040] Preferably, the amount of the oxygen free radical capture multifunctional additive added is 4-6% of the mass of the second injection electrolyte.
[0041] Preferably, the structural formula of the cyclic ester lithium salt includes At least one of, wherein R1, R2 and R3 are all saturated or unsaturated alkyl groups.
[0042] When R1, R2 and R3 are methyl groups, It is 5-trimethylborate lithium-1,3,2-dioxathiazole-2,2-dioxide.
[0043] Preferably, the preparation method of 5-trimethylborate lithium-1,3,2-dioxathiacyclohexane-2,2-dioxide comprises mixing triethylamine, 5-chloro-2,2-dioxo-1,3,2-dioxathiacyclohexane and a first solvent to form a reaction system, installing a condensation reflux tube, adding a bistriphenylphosphine palladium dichloride catalyst to the reaction system, dissolving trimethyl borate and lithium hydroxide in a second solvent, adding the solvent to the reaction system, heating at 60-70° C., condensing and refluxing for 10-20 hours, cooling to 20-30° C., evaporating and concentrating the solution, and precipitating with ether to obtain a purified product;
[0044] Preferably, the volume mass ratio of triethylamine, 5-chloro-2,2-dioxo-1,3,2-dioxathiazole and the first solvent is 13-17 ml: 2-3 g: 10-14 ml;
[0045] Preferably, the mass volume ratio of trimethyl borate, lithium hydroxide and the second solvent is 1.5-2 g: 0.3-0.7 g: 6-10 ml;
[0046] Preferably, the first solvent and the second solvent are both tetrahydrofuran.
[0047] In an alternative embodiment, The preparation method comprises: adding methanesulfonic acid, boric acid, lithium borate and toluene solvent into a flask purged with nitrogen, installing a condenser reflux tube, stirring evenly, heating to 90-110° C., condensing and reflux for 6 hours, cooling to 20-30° C., filtering the reaction solution to separate the solid product, washing the product with acetonitrile and drying it to obtain the final product;
[0048] Preferably, the mass ratio of methanesulfonic acid, boric acid, lithium borate and toluene solvent is 1.4-1.6:1.4-1.6:0.5-0.7:9-11.
[0049] The amount of film-forming additive added is 2-3% of the mass of one injection of electrolyte; preferably, the film-forming additive includes but is not limited to at least one of vinylene carbonate VC, fluoroethylene carbonate FEC, tris(trimethylsilyl) phosphate TMSP, and tris(trimethylsilyl) borate TMSB.
[0050] The concentration of lithium salt in the first electrolyte and the second electrolyte is 0.8-1.2 mol / L; preferably, the lithium salt includes but is not limited to at least one of lithium hexafluorophosphate LiPF6, lithium tetrafluoroborate LiBF4, lithium bis(fluorosulfonyl)imide LiFSI, lithium bis(trifluoromethylsulfonyl)imide LiTFSI, lithium perchlorate LiClO4, lithium difluorooxalatoborate LiODFB, lithium difluorobis(oxalatophosphate LiODFP), lithium difluorophosphate LiPO2F2, and lithium dioxalatoborate LiBOB.
[0051] The carbonate solvents include but are not limited to at least two of ethylene carbonate EC, propylene carbonate PC, diethyl carbonate DEC, dimethyl carbonate DMC and ethyl methyl carbonate EMC; preferably, the carbonate solvents include 20-40% ethylene carbonate, 20-40% ethyl methyl carbonate and 30-50% dimethyl carbonate by volume.
[0052] In addition, the present invention provides a method for injecting the electrolyte suitable for the battery lithium replenishment system, which includes injecting a shot of electrolyte into a soft-pack battery of the lithium replenishment system, then performing formation, primary exhaust, high-temperature aging and secondary exhaust on the soft-pack battery of the lithium replenishment system, and then injecting a second shot of electrolyte.
[0053] In the present invention, after high-temperature aging and secondary exhaust, the second injection of electrolyte is performed. The lithium supplement will decompose and produce a large amount of oxygen in the formation stage. If the oxygen free radical capture additive is directly added during the injection, the additive will be completely consumed during the formation and will not play a protective role in the later stage. There have been reports of two injections before, in which TMP or nitroxide free radical-type free radical capture additives are added after formation and then subjected to high-temperature aging. However, in the high-temperature aging stage, the reaction of the incompletely formed additive will still continue, consuming the free radical capture additive prematurely and weakening its function. Therefore, the present invention adopts a scheme of performing two injections after high-temperature aging and exhaust. After aging, the film-forming reaction has ended and a stable SEI film has been formed. At this time, adding the free radical capture additive can ensure that the additive has enough content in the later cycle for continuous consumption and absorbs the oxygen free radicals generated in the later period.
[0054] Among them, the total amount of electrolyte injection for the first injection and the second injection is 3.5-4.5g / Ah;
[0055] And / or, the positive electrode material of the lithium supplement system soft-pack battery includes lithium iron phosphate, ternary material, lithium cobalt oxide or lithium manganese oxide, and the negative electrode material includes graphite, silicon carbon or silicon oxygen.
[0056] In addition, the present invention also provides a lithium-ion battery, which uses the above-mentioned electrolyte injection method suitable for the battery lithium replenishment system to replenish lithium.
[0057] The features and performance of the present invention are further described in detail below in conjunction with the embodiments.
[0058] Example 1
[0059] The present embodiment provides an electrolyte suitable for a battery lithium replenishment system, which includes a first injection of electrolyte 90% and a second injection of electrolyte 10%, wherein the composition of the first injection of electrolyte includes 1M LiPF6+EC / EMC / DMC (30:30:40vol%)+2.22% VC, and the composition of the second injection of electrolyte includes 1MLiPF6+EC / EMC / DMC (30:30:40vol%)+5% 5-trimethylborate lithium-1,3,2-dioxathiacyclohexane-2,2-dioxide.
[0060] The preparation method includes: adding conductive lithium salt lithium hexafluorophosphate (LiPF6) at a concentration of 1 mol / L into a mixed solvent of ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) (EC / EMC / DMC=30:30:40 vol%), fully dissolving to form a solution, and then adding vinylene carbonate (VC) with a mass ratio of 2.22% to form an electrolyte.
[0061] The conductive lithium salt lithium hexafluorophosphate (LiPF6) is added to a mixed solvent of ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) (EC / EMC / DMC=30:30:40vol%) at a concentration of 1 mol / L, and after being fully dissolved to form a solution, 5% by mass of 5-trimethylborate lithium-1,3,2-dioxathiazole-2,2-dioxide is added thereto to form a second electrolyte.
[0062] Among them, the preparation method of 5-trimethylborate lithium-1,3,2-dioxathiacyclohexane-2,2-dioxide includes: adding 15mL triethylamine, 2.5g 5-chloro-2,2-dioxo-1,3,2-dioxathiacyclohexane and 12mL tetrahydrofuran to a 100mL round-bottom flask, installing a condensing reflux tube, and adding 0.5g of bistriphenylphosphine palladium dichloride catalyst to the reaction system. Dissolve 1.7g trimethyl borate and 0.5g lithium hydroxide in 8mL tetrahydrofuran and add them to the reaction system with a syringe. Heat at 65°C, condense and reflux for 15 hours, and cool to 25°C. Evaporate and concentrate the solution, and precipitate with ether (50mL*4) to obtain a purified product.
[0063] Injection method: inject the above electrolyte into a 5Ah lithium supplement system soft pack battery, the positive electrode of the battery is LFP+2wt% LFO, the negative electrode is graphite, and the injection coefficient is 4g / Ah. In the first injection, inject 90wt% of the total electrolyte into the first injection, and the battery is formed (charged to 4.0V with a current of 200mA), vented once (cut a small hole in the aluminum plastic film of the battery core for venting and then sealed twice), aged at high temperature (aged at 45°C for 12 hours), vented twice (operated in the same venting as the first), and then add a second injection of electrolyte with a total amount of 10wt%, and perform DC impedance (DCR), cycle, storage and other performance tests after standing.
[0064] Example 2
[0065] This embodiment is basically the same as embodiment 1, except that the oxygen free radical capture multifunctional additive in this embodiment is The preparation method comprises the following steps: adding 1.5 g of methanesulfonic acid, 1.5 g of boric acid, 0.6 g of lithium borate and 10 g of toluene solvent into a flask purged with nitrogen, installing a condenser reflux tube, stirring evenly, heating to 100° C., condensing and reflux for 6 hours, cooling to 25° C., filtering the reaction solution to separate a solid product, washing the product with acetonitrile and drying it to obtain a final product.
[0066] Example 3
[0067] This embodiment is basically the same as Embodiment 1, except that the multifunctional additive for capturing oxygen free radicals in this embodiment is 5-triethyllithium borate-1,3,2-dioxathiazole-2,,2-dioxide.
[0068] Example 4
[0069] This embodiment is basically the same as Embodiment 1, except that, in this embodiment, the multifunctional additive for capturing oxygen free radicals is 5-triacetylene lithium borate-1,3,2-dioxathiazole-2,,2-dioxide.
[0070] Example 5
[0071] This embodiment is substantially the same as the embodiment 1, except that it includes one injection of electrolyte 95% and two injections of electrolyte 5%.
[0072] Example 6
[0073] This embodiment is substantially the same as the embodiment 1, except that it includes one injection of electrolyte solution 85% and two injections of electrolyte solution 15%.
[0074] Example 7
[0075] This embodiment is basically the same as Embodiment 1, except that, in this embodiment, the composition of the second injection electrolyte includes 1M LiPF6+EC / EMC / DMC (30:30:40 vol%)+6% 5-trimethylborate lithium-1,3,2-dioxathiazole-2,2-dioxide.
[0076] Example 8
[0077] This embodiment is basically the same as Embodiment 1, except that, in this embodiment, the composition of the second injection electrolyte includes 1M LiPF6+EC / EMC / DMC (30:30:40 vol%)+4% 5-trimethylborate lithium-1,3,2-dioxathiazole-2,2-dioxide.
[0078] Example 9
[0079] This embodiment is basically the same as Embodiment 1, except that, in this embodiment, the composition of one shot of electrolyte includes 1M lithium tetrafluoroborate + propylene carbonate / diethyl carbonate (50:50 vol%) + 2.22% fluoroethylene carbonate, and the composition of the second shot of electrolyte includes 1M lithium tetrafluoroborate + propylene carbonate / diethyl carbonate (50:50 vol%) + 5% 5-trimethyllithium borate-1,3,2-dioxathiacyclohexane-2,2-dioxide.
[0080] Example 10
[0081] This embodiment is basically the same as Embodiment 1, except that, in this embodiment, the composition of one injection of electrolyte includes 1M lithium bis(fluorosulfonyl)imide + ethylene carbonate / diethyl carbonate / ethyl methyl carbonate (20:20:60 vol%) + 2.22% tris(trimethylsilyl)borate, and the composition of the second injection of electrolyte includes 1M lithium bis(fluorosulfonyl)imide + ethylene carbonate / diethyl carbonate / ethyl methyl carbonate (20:20:60 vol%) + 5% 5-trimethylborate lithium-1,3,2-dioxathiacyclohexane-2,2-dioxide.
[0082] Comparative Example 1
[0083] The electrolyte composition suitable for the battery lithium replenishment system in this comparative example is the same as that in Example 1, except that the second injection of electrolyte in this comparative example is added after the first exhaust and before high-temperature aging.
[0084] Specifically including: the electrolyte in this comparative example includes one injection of electrolyte 90% and two injections of electrolyte 10%, wherein the composition of one injection of electrolyte includes 1M LiPF6+EC / EMC / DMC (30:30:40vol%)+2.22% VC, and the composition of the two injections of electrolyte includes 1M LiPF6+EC / EMC / DMC (30:30:40vol%)+5% 5-trimethylborate lithium-1,3,2-dioxathiazole-2,2-dioxide.
[0085] Injection method: The above electrolyte is injected into a 5Ah lithium supplement system soft pack battery, the positive electrode of the battery is LFP+2wt% LFO, the negative electrode is graphite, and the injection coefficient is 4g / Ah. In the first injection, a first injection of electrolyte with a total electrolyte content of 90wt% is injected, the battery is formed and exhausted once, and then a second injection of electrolyte with a total content of 10wt% is added, followed by high temperature aging and secondary exhaust, and after standing, DC impedance (DCR), cycle, storage and other performance tests are performed.
[0086] Comparative Example 2
[0087] This comparative example is basically the same as Example 1, except that the electrolyte in this comparative example comprises a mixture of a first injection electrolyte and a second injection electrolyte as a mixed electrolyte, and a single injection is directly performed.
[0088] Specifically, the mixed electrolyte in this comparative example includes 1M LiPF6+EC / EMC / DMC (30:30:40 vol%)+2% VC+0.5% 5-trimethylborate lithium-1,3,2-dioxathiazole-2,2-dioxide.
[0089] Injection method: Inject the above electrolyte into a 5Ah lithium supplement system soft pack battery, the battery positive electrode is LFP + 2wt% LFO, the negative electrode is graphite, and the injection coefficient is 4g / Ah. During the first injection, inject 100wt% of the total electrolyte mixed electrolyte, and the battery is formed, exhausted once, aged at high temperature and exhausted twice, and then left to stand for DC impedance (DCR), cycle, storage and other performance tests.
[0090] Comparative Example 3
[0091] This comparative example is substantially the same as Example 1, except that this comparative example uses only one injection of electrolyte for one injection.
[0092] Specifically including: the electrolyte in this comparative example includes: 1M LiPF6+EC / EMC / DMC (30:30:40 vol%)+2% VC.
[0093] Injection method: Inject the above electrolyte into a 5Ah lithium supplement system soft pack battery, the positive electrode of the battery is LFP+2wt%LFO, the negative electrode is graphite, and the injection coefficient is 4g / Ah. After injection, the battery is formed, exhausted, and then aged at high temperature. After aging, the DC resistance (DCR), cycle, storage and other performance tests are performed.
[0094] Comparative Example 4
[0095] This comparative example is basically the same as Example 1, except that in this comparative example, the additive in the two injections of electrolyte is different from that in Example 1, and the additive in this comparative example is methyl phosphite.
[0096] Specifically including: the electrolyte in this comparative example includes one injection of electrolyte 90% and two injections of electrolyte 10%, wherein the composition of one injection of electrolyte includes 1M LiPF6+EC / EMC / DMC (30:30:40vol%)+2.22% VC, and the composition of the two injections of electrolyte includes 1M LiPF6+EC / EMC / DMC (30:30:40vol%)+5% methyl phosphite.
[0097] The conductive lithium salt lithium hexafluorophosphate (LiPF6) is added to a mixed solvent of ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) at a concentration of 1 mol / L (EC / EMC / DMC=30:30:40 vol%), and after being fully dissolved to form a solution, 5% by mass of methyl phosphite (TMP) is added thereto to form a second injection electrolyte.
[0098] Injection method: Inject the above electrolyte into a 5Ah lithium supplement system soft pack battery, the battery positive electrode is LFP + 2wt% LFO, the negative electrode is graphite, and the injection coefficient is 4g / Ah. In the first injection, inject 90wt% of the total electrolyte into the first injection, the battery is formed, the first exhaust, high temperature aging, the second exhaust, and then add the second injection of 10wt% of the total electrolyte. After standing, perform DC impedance (DCR), cycle, storage and other performance tests.
[0099] Comparative Example 5
[0100] This comparative example is basically the same as Example 1, except that in this comparative example, the additives of the two electrolyte injections are compounds containing sulfuric acid groups and boron, respectively, and the specific additives are: propylene sulfate and lithium bis(oxalatoborate).
[0101] Specifically including: the electrolyte in this comparative example includes one injection of electrolyte 90% and two injections of electrolyte 10%, wherein the composition of one injection of electrolyte includes 1M LiPF6+EC / EMC / DMC (30:30:40vol%)+2.22% VC, and the composition of the two injections of electrolyte includes 1M LiPF6+EC / EMC / DMC (30:30:40vol%)+2.5% propylene sulfate+2.5% lithium bis(oxalatoborate) (LiBOB).
[0102] Injection method: Inject the above electrolyte into a 5Ah lithium supplement system soft pack battery, the battery positive electrode is LFP + 2wt% LFO, the negative electrode is graphite, and the injection coefficient is 4g / Ah. In the first injection, inject 90wt% of the total electrolyte into the first injection, the battery is formed, the first exhaust, high temperature aging, the second exhaust, and then add the second injection of 10wt% of the total electrolyte. After standing, perform DC impedance (DCR), cycle, storage and other performance tests.
[0103] Comparative Example 6
[0104] This comparative example is basically the same as Example 1, except that, in this comparative example, the composition of the second injection electrolyte includes 1M LiPF6+EC / EMC / DMC (30:30:40 vol%)+7% 5-trimethylborate lithium-1,3,2-dioxathiazole-2,2-dioxide.
[0105] Experimental example
[0106] The above-mentioned embodiments and comparative examples were subjected to performance tests such as DC resistance (DCR), cycling, and storage, wherein the DC resistance (DCR) test method includes: discharging at 2.5C current pulse for 30 seconds at 50% SOC, and calculating the discharge resistance. The cycling test method includes: charging and discharging cycles at 1C current at 45°C. The storage test method includes: testing the volume of the soft-pack battery cell before storage, and testing the volume expansion rate of the soft-pack battery cell after storage at 55°C for 20 days. Please refer to Table 1 for the test results.
[0107] Table 1. Statistics of performance test results for different examples
[0108]
[0109]
[0110] As can be seen from the above table, in the present invention, by introducing an oxygen free radical capture multifunctional additive (5-trimethylborate lithium-1,3,2-dioxathiazole-2,2-dioxide), it can introduce boric acid groups, sulfuric acid groups and / or sulfonic acid groups. The boric acid groups help to reduce the gas production of the lithium supplement system. At the same time, the introduction of the additive can form an SEI film containing the S element, which helps to improve the warm cycle performance and enhance the stability of the SEI film.
[0111] As can be seen from Comparative Example 1, the above-mentioned oxygen free radical capture multifunctional additive is not effective when added after formation and before aging. The introduction of Example 1 after high-temperature aging and exhaust can avoid premature consumption in the early stage, which helps to improve the gas production in the later storage. As can be seen from Comparative Example 2, in the case of only one injection, even if the electrolyte contains the above-mentioned oxygen free radical capture multifunctional additive, its effect is significantly lower than that of Example 1. As can be seen from Comparative Example 3, in the case of only one injection, if the above-mentioned oxygen free radical capture multifunctional additive is not included, its effect is significantly lower than that of Example 1 and Comparative Example 2. As can be seen from Comparative Example 4, compared with conventional high-impedance oxygen free radical capture additives, 5-trimethylborate lithium-1,3,2-dioxathioxane-2,2-dioxide additives have lower gas production, lower DCR, and better high-temperature cycle performance. As can be seen from Comparative Example 5, without adding 5-trimethylborate lithium-1,3,2-dioxathioxane-2,2-dioxide additives, the introduction of two additives containing sulfate esters and boric acid groups will increase the system DCR and affect its cycle performance. It can be seen from Comparative Example 6 that when the amount of the new additive 5-trimethylborate lithium-1,3,2-dioxathiazole-2,2-dioxide added is too much, the DCR increases and the high temperature cycle capacity retention rate deteriorates.
[0112] In summary, the electrolyte suitable for the battery lithium supplement system provided by the present invention is provided with one injection of electrolyte and two injections of electrolyte, and a film-forming additive is introduced into one injection of electrolyte, and a multifunctional additive for capturing oxygen free radicals containing boron atoms, sulfate groups and / or sulfonic acid groups is introduced into the two injections of electrolyte. Among them, the boron atom has an empty p orbital and is relatively electrophilic, which can capture the oxygen free radicals generated by the decomposition of the lithium supplement agent, prevent it from forming an intermediate with the electrolyte solvent, and produce reducing gas at the negative electrode, causing further side reactions. The additive can also participate in the repair of the SEI film in the later stages of circulation and storage, and can form a film at both the positive and negative electrodes, protect the positive and negative electrodes, and reduce the probability of the solvent and oxygen free radicals being oxidized and reduced to produce gas. The electrolyte avoids the problem of increased impedance introduced by conventional additives, and the multifunctional additive is a lithium salt additive. After introduction, the electrolyte is more conducive to lithium ion transmission and can provide additional lithium ions to make up for a certain loss of active lithium. The sulfuric acid / sulfonic acid groups in the structure participate in the film formation to form a SEI film containing S, which helps to reduce impedance, improve the high temperature performance of the battery cell, and enhance the mechanical stability of the SEI film. In addition, the electrolyte adopts a secondary injection method, and the secondary injection step is placed after high temperature aging. The lithium supplement will decompose and produce a large amount of oxygen in the formation stage. If the oxygen free radical capture additive is directly added during the injection, the additive will be consumed during the formation and will not play a protective role in the later stage. There have been reports of two injections before, in which TMP or nitroxide free radical-type free radical capture additives are added after formation and then subjected to high temperature aging. However, in the high temperature aging stage, the reaction of the incompletely formed additive will continue, consuming the free radical capture additive prematurely and weakening its function. Therefore, the present invention adopts a scheme of performing two injections after high temperature aging and exhaust. After aging, the film formation reaction has ended and a stable SEI film has been formed. At this time, the addition of free radical capture additives can ensure that the additive has enough content in the later cycle for continuous consumption and absorbs the oxygen free radicals generated in the later period.
[0113] The above are only preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.
Claims
1. An electrolyte suitable for a battery lithium supplement system, characterized in that: It includes one injection of electrolyte and two injections of electrolyte, both of which include carbonate solvents and lithium salts, the one injection of electrolyte also includes a film-forming additive, and the two injections of electrolyte also include a multifunctional additive for capturing oxygen free radicals, and the multifunctional additive for capturing oxygen free radicals is a cyclic ester lithium salt compound, wherein the cyclic ester lithium salt compound contains a boron atom and also contains at least one of a sulfate group and a sulfonic acid group.
2. The electrolyte suitable for a battery lithium replenishment system according to claim 1, characterized in that: The mass percentage of the first electrolyte injection to the electrolyte suitable for the battery lithium replenishment system is 85-95%, and the mass percentage of the second electrolyte injection to the electrolyte suitable for the battery lithium replenishment system is 5-15% respectively; Preferably, the amount of the oxygen free radical capture multifunctional additive added is 4-6% of the mass of the second injection electrolyte; Preferably, the structural formula of the cyclic ester lithium salt includes At least one of, wherein R1, R2 and R3 are all saturated or unsaturated alkyl groups.
3. The electrolyte suitable for battery lithium replenishment system according to claim 2, characterized in that: Said 5-trimethylborate lithium-1,3,2-dioxathiazole-2,2-dioxide; Preferably, the preparation method of 5-trimethylborate lithium-1,3,2-dioxathiacyclohexane-2,2-dioxide comprises mixing triethylamine, 5-chloro-2,2-dioxo-1,3,2-dioxathiacyclohexane and a first solvent to form a reaction system, installing a condensation reflux tube, adding a bistriphenylphosphine palladium dichloride catalyst to the reaction system, dissolving trimethyl borate and lithium hydroxide in a second solvent, adding the solvent to the reaction system, heating at 60-70° C., condensing and refluxing for 10-20 hours, cooling to 20-30° C., evaporating and concentrating the solution, and precipitating with ether to obtain a purified product; Preferably, the volume mass ratio of the triethylamine, the 5-chloro-2,2-dioxo-1,3,2-dioxathiazole and the first solvent is 13-17 ml: 2-3 g: 10-14 ml; Preferably, the mass volume ratio of the trimethyl borate, the lithium hydroxide and the second solvent is 1.5-2 g: 0.3-0.7 g: 6-10 ml; Preferably, the first solvent and the second solvent are both tetrahydrofuran.
4. The electrolyte suitable for a battery lithium replenishment system according to claim 2, characterized in that: Said The preparation method comprises: adding methanesulfonic acid, boric acid, lithium borate and toluene solvent into a flask purged with nitrogen, installing a condenser reflux tube, stirring evenly, heating to 90-110° C., condensing and reflux for 6 hours, cooling to 20-30° C., filtering the reaction solution to separate the solid product, washing the product with acetonitrile and drying it to obtain the final product; Preferably, the mass ratio of the methanesulfonic acid, the boric acid, the lithium borate and the toluene solvent is 1.4-1.6:1.4-1.6:0.5-0.7:9-11.
5. The electrolyte suitable for a battery lithium replenishment system according to claim 1, characterized in that: The amount of the film-forming additive added is 2-3% of the mass of the electrolyte solution; Preferably, the film-forming additive includes at least one of vinylene carbonate, fluoroethylene carbonate, tris(trimethylsilyl)phosphate and tris(trimethylsilyl)borate.
6. The electrolyte suitable for battery lithium replenishment system according to claim 1, characterized in that: The concentration of the lithium salt in the first electrolyte and the second electrolyte is 0.8-1.2 mol / L; Preferably, the lithium salt includes at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethylsulfonyl)imide, lithium perchlorate, lithium difluorooxalatoborate, lithium difluorobis(oxalatophosphate), lithium difluorophosphate and lithium dioxalatoborate.
7. The electrolyte suitable for battery lithium replenishment system according to claim 1, characterized in that: The carbonate solvent includes at least two of ethylene carbonate, propylene carbonate, diethyl carbonate, dimethyl carbonate and ethyl methyl carbonate; Preferably, the carbonate solvent comprises, by volume percentage, 20-40% ethylene carbonate, 20-40% ethyl methyl carbonate and 30-50% dimethyl carbonate.
8. A method for injecting electrolyte suitable for a battery lithium replenishment system as claimed in any one of claims 1 to 7, characterized in that: The first injection of electrolyte is injected into a lithium supplement system soft-pack battery, and then the lithium supplement system soft-pack battery is subjected to formation, primary exhaust, high-temperature aging and secondary exhaust, and then the second injection of electrolyte is injected.
9. The method for injecting electrolyte suitable for a battery lithium supplementation system according to claim 8, characterized in that: The total amount of the first electrolyte injection and the second electrolyte injection is 3.5-4.5 g / Ah; And / or, the positive electrode material of the lithium supplement system soft-pack battery includes lithium iron phosphate, ternary material, lithium cobalt oxide or lithium manganese oxide, and the negative electrode material includes graphite, silicon carbon or silicon oxygen.
10. A lithium ion battery, characterized in that: The lithium replenishment is carried out by using the electrolyte injection method suitable for the battery lithium replenishment system as described in any one of claims 8 to 9.