Electrolyte capable of inhibiting gas production of lithium-rich lithium ferrite and lithium ion battery

Abstract

The invention discloses an electrolyte capable of inhibiting gas production of lithium-rich lithium ferrite and a lithium ion battery, and belongs to the field of lithium ion batteries. An electrolyte capable of inhibiting gas production of lithium-rich lithium ferrite comprises a lithium salt, an organic solvent and an additive, the additive comprises a deoxidant, and the deoxidant has a sulfite group and a phosphite group. According to the electrolyte capable of inhibiting gas production of the lithium-rich lithium ferrite disclosed by the invention, due to the introduction of a sulfite group in the added deoxidant, not only can oxygen free radicals be absorbed, but also an interfacial film with relatively low impedance can be formed, the problem of high film-forming impedance of a phosphite group is relieved, and the rate capability of a lithium ion battery is ensured.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium ion batteries, and in particular to an electrolyte and a lithium ion battery capable of inhibiting gas generation of lithium-rich lithium ferrite. Background Art

[0002] Compared to other chemical energy storage devices, lithium-ion batteries have advantages such as higher energy density, faster charge and discharge rates, and no memory effect. Due to their inherent advantages, lithium-ion batteries are widely used in mobile phones, laptops, fuel vehicles, new energy vehicles, and industrial energy storage. Although lithium-ion batteries are widely used in various fields, their inherent lifespan issues limit the expansion of their application areas, especially in the field of industrial energy storage. Since the operating life of industrial energy storage is as long as 20 years, lithium-ion batteries are required to support a cycle life requirement of more than 10,000 times. According to conventional lithium-ion battery technology, the maximum lifespan of lithium-ion batteries is 8,000 cycles. Developing a technology with a cycle life of more than 10,000 times is technically difficult, and lithium supplements must be used. Lithium supplements continuously release active lithium to replenish the lithium ions consumed during the cycle, thereby achieving the purpose of increasing the cycle life of lithium-ion batteries.

[0003] Common lithium supplements include lithium-rich ferrite (LFO) and lithium-rich nickel oxide (LNO). LFO is popular in the market due to its high gram capacity. However, LFO suffers from gassing issues during storage, hindering its mass adoption. Addressing LFO gassing requires understanding its mechanism. The industry consensus is that gassing in LFO (molecular formula Li5FeO4) pre-lithiation agents originates from oxygen or peroxides generated by the decomposition of LFO. Suppressing or removing these oxygen and peroxides is crucial to addressing this issue.

[0004] There are two conventional methods to reduce the gas production of lithium-rich ferrite (LFO) pre-lithium agent, one is the direct optimization method and the other is the indirect optimization method. The direct optimization method refers to the direct optimization of LFO, including doping, coating and superlattice. For example, patent document CN118970048A discloses the use of doping and surface coating methods to improve the gas production problem of lithium-rich ferrite (LFO). Specific operation: doping metal elements such as titanium, tungsten, nickel, and cobalt into the lithium-rich ferrite (LFO) body. The surface of the lithium-rich ferrite (LFO) is then coated with a carbon layer doped with elements such as boron, sulfur, and phosphorus. By combining doping and coating, the discharge capacity is significantly improved and the gas production is reduced. However, this method has high requirements on the production process, complex process control, and high production costs.

[0005] The indirect optimization method refers to optimizing the gas production performance of lithium-rich ferrite (LFO) by mixing in substances that reduce the gas production of lithium-rich ferrite (LFO). For example, patent document CN117954694A proposes a class of alkyl-containing phosphites. By combining this type of phosphite with triethylenediamine, it not only improves the oxygen release problem of lithium ferrite supplement during long-term charging, but also suppresses the problems such as SEI film rupture caused by the volume expansion of silicon-based negative electrode materials, and the electrolyte has better oxidation resistance, thereby improving the cycle performance, high temperature performance and hot box performance of silicon negative electrode lithium-ion batteries. However, the phosphite and triethylenediamine used will significantly increase the impedance of the negative electrode interface, thereby increasing the battery impedance. Compared with the direct optimization method, the indirect optimization method has simple process control, high operability and cost advantages, but the selection of new substances is strict, and the rate performance and life cannot be balanced. Summary of the Invention

[0006] The object of the present invention is to provide an electrolyte that takes into account both the rate performance and life of a lithium-ion battery and can inhibit the gas production of lithium-rich lithium ferrite; another object of the present invention is to provide a lithium-ion battery with excellent cycle and storage life.

[0007] The present invention discloses an electrolyte capable of inhibiting gas generation of lithium-rich lithium ferrite, comprising a lithium salt, an organic solvent, and an additive. The additive comprises an oxygen scavenger having a structural formula (I):

[0008] (I);

[0009] Wherein, R1 is selected from one of an alkyl group having 1 to 12 carbon atoms, an alkenyl group having 1 to 10 carbon atoms, an alkynyl group having 1 to 10 carbon atoms, a halogen substituent, a phenyl group, an aryl group, a heterocyclic group, an ether group, a cyano group, an azide group, a sulfur-containing group, a phosphorus-containing group, a silicon-containing group, a nitrogen-containing group, and a boron-containing group.

[0010] Oxygen scavengers are added to the electrolyte. These compounds possess two strong reducing groups: a sulfite group and a phosphite group. The sulfur element in the phosphite group is in a positive tetravalent state and readily loses two electrons in response to oxidants, forming a hexavalent sulfur state. The phosphorus element in the phosphite group is in a positive trivalent state and readily loses two electrons in response to oxidants, forming a pentavalent phosphate.

[0011] The mechanism of gas production by lithium-rich iron phosphate (LFO) is that lithium-rich iron phosphate (LFO) forms oxygen or peroxide during the charging process. These compounds have extremely strong oxidizing ability and can easily oxidize the carbonate in the electrolyte into carbon dioxide and carbon monoxide. Since the deoxidizer in the present invention has a strong reducing ability, it can be reduced with the carbonate by oxygen or peroxide first, and the reduction products are sulfate and phosphate compounds. These reduction products are liquid or solid substances, which reduce the gas production of lithium-rich iron phosphate (LFO) pre-lithium agent. Deoxidizers containing sulfite and phosphite groups are a type of film-forming additive with excellent performance, which has little effect on the performance of lithium-ion batteries. By using this new deoxidizing additive, the gas production of lithium-rich iron phosphate (LFO) pre-lithium agent is reduced, and the cycle and storage performance of lithium-ion batteries are improved.

[0012] Furthermore, R1 is selected from one of trifluoromethyl, phenyl and cyano.

[0013] Furthermore, the content of the deoxidizer in the electrolyte is 0.3-5wt%.

[0014] The organic solvent includes dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, ethylene carbonate, propylene carbonate, vinylene carbonate, vinyl sulfite, methyl acetate, ethyl acetate, ethyl propionate, propyl propionate, methyl propionate, propyl formate, fluorobenzene, xylene, toluene, fluoroethylene carbonate, fluoroethyl methyl carbonate, fluorodimethyl carbonate, fluorodiethyl carbonate, trimethyl phosphate, triethyl phosphate, tripropyl phosphate, trimethyl phosphite, triethyl phosphite, tripropyl phosphite, tetrahydrofuran, acetonitrile, sulfolane, dimethyl sulfoxide, 1,2-dimethoxyethane, etc.

[0015] The lithium salt includes one or more of lithium hexafluorophosphate, lithium bis(trifluoromethanesulfonylimide), lithium bis(oxalatoborate), lithium tetrafluoroborate, lithium difluorooxalatoborate, lithium difluorophosphate, lithium bis(trifluoromethanesulfonylimide), lithium perchlorate, and lithium hexafluoroarsenate.

[0016] The additives also include conventional film-forming additives, which include one or more of 1,3-propane sultone, vinyl sulfate, methylene disulfonate, propylene sultone, tris(trimethylsilane) phosphate, propylene sulfate, tris(trimethylsilane) borate, lithium bis(oxalatoborate), lithium tetrafluoroborate, lithium difluorooxalatoborate, lithium difluorophosphate, lithium difluorooxalatophosphate, fluoroethylene carbonate, vinyl ethylene carbonate, and lithium difluorooxalatophosphate.

[0017] Furthermore, R1 is selected from trifluoromethyl; and the content of the oxygen scavenger in the electrolyte is 0.5-1 wt%.

[0018] At this time, the battery rate performance, capacity retention rate, and gas generation suppression performance are the best.

[0019] Furthermore, the additives also include vinylene carbonate (VC), 1,3-propane sultone (PS), and lithium difluorophosphate (LiPF2O2).

[0020] The combination of the oxygen scavenger and conventional additives can take into account the rate performance of the lithium ion battery.

[0021] Furthermore, the content of vinylene carbonate in the electrolyte is 0.3-10 wt %, the content of 1,3-propane sultone in the electrolyte is 0.3-5 wt %, and the content of lithium difluorophosphate in the electrolyte is 0.1-2 wt %.

[0022] Furthermore, the organic solvent includes ethylene carbonate, ethyl methyl carbonate, and dimethyl carbonate.

[0023] Furthermore, the mass ratio of ethylene carbonate, ethyl methyl carbonate and dimethyl carbonate in the organic solvent is (0.8-1.2):(1-1.5):1.

[0024] Furthermore, the lithium salt includes lithium hexafluorophosphate.

[0025] The present invention also discloses a lithium-ion battery, comprising a positive electrode sheet, a negative electrode sheet, a separator and the electrolyte as described above; the positive electrode sheet comprises lithium-rich lithium ferrite.

[0026] Among them, the positive electrode sheet is composed of aluminum foil, active material, lithium supplement agent, conductive agent, and binder. The positive electrode active material includes one or more of lithium iron phosphate, nickel cobalt manganese ternary material, nickel cobalt aluminum ternary material, lithium manganese-rich oxide, lithium manganese iron phosphate, lithium cobalt oxide, and lithium nickel oxide.

[0027] The negative electrode sheet is composed of copper foil, active material, conductive agent and binder, wherein the active material includes one or more of artificial graphite, natural graphite, soft carbon, hard carbon, silicon, silicon carbon and silicon oxide.

[0028] The diaphragms include PP diaphragms, PE diaphragms, PP / PE diaphragms, PP / PE / PP diaphragms, ceramic diaphragms, and rubber-coated diaphragms.

[0029] The present invention provides an electrolyte capable of inhibiting gas production in lithium-rich lithium ferrite. By adding a deoxidizer containing a sulfite group and a phosphite group, the introduction of the sulfite group can not only absorb oxygen free radicals, but also form an interface film with low impedance, thereby alleviating the problem of high film-forming impedance of the phosphite group and ensuring the rate performance of the lithium-ion battery. Compared with the method of reducing gas production by optimizing the process of lithium-rich lithium ferrite, the deoxidizer has the advantages of low operational difficulty and low cost. Compared with other deoxidizers, the deoxidizer containing sulfite and phosphite has a significant deoxidation effect and does not deteriorate the rate performance of the lithium-ion battery. DETAILED DESCRIPTION

[0030] In order to make the technical solution of the present invention clearer, the present invention is further described in detail below with reference to specific embodiments.

[0031] The oxygen scavenger compound having the structure of formula (I) used in this embodiment is mainly synthesized from thionyl chloride, erythritol, and phosphite. The specific synthesis steps are as follows:

[0032] .

[0033] The synthesis method of oxygen scavenger T1 is as follows:

[0034] .

[0035] The synthesis method of oxygen scavenger T2 is as follows:

[0036] .

[0037] The synthesis method of oxygen scavenger T3 is as follows:

[0038] .

[0039] The preparation steps of lithium-ion dry cell are as follows:

[0040] The positive electrode sheet is prepared by selecting lithium iron phosphate as the positive electrode active material and mixing it with lithium iron oxide (LFO), conductive carbon black, and polyvinylidene fluoride (PVDF) as a binder in a mass ratio of 92.5:3:2:2.5. Specifically, the lithium iron phosphate, lithium iron oxide (Li5FeO4) (LFO), conductive carbon black, and PVDF are first dispersed in an appropriate amount of N-methylpyrrolidone. The mixture is then thoroughly stirred according to the homogenization step. The evenly dispersed positive electrode slurry is evenly coated on aluminum foil. The positive electrode sheet is then baked, rolled, slit, and punched.

[0041] The negative electrode sheet preparation method involves selecting artificial graphite as the negative electrode active material and placing it into a slurry tank with conductive carbon black, styrene-butadiene rubber (SBR), and sodium carboxymethyl cellulose (CMC) in a mass ratio of 96:1:2:1. Following the slurrying process, a uniformly dispersed negative electrode slurry is prepared. The negative electrode slurry is then evenly coated onto copper foil. The negative electrode sheet is then produced through baking, roller pressing, slitting, and punching.

[0042] The diaphragm used was a commercially available polyethylene diaphragm.

[0043] After punching the positive and negative electrodes, bake the positive electrode in an oven at 110-140°C and the negative electrode in an oven at 90-100°C for 20-30 hours. When the moisture content of the electrodes meets the requirements, the positive and negative electrodes and the separator are placed in a laminating machine to form bare cells. The bare cells are then encapsulated in stamped aluminum-plastic film bags or lithium-ion dry batteries.

[0044] Example 1

[0045] Prepare electrolyte:

[0046] Control the moisture content in the glove box to below 10 ppm, and the moisture content in the organic solvent to below 10 ppm. Using a percentile balance, accurately weigh 30 g of ethylene carbonate, 40 g of ethyl methyl carbonate, and 30 g of dimethyl carbonate into an aluminum bottle. Stir thoroughly and place in a 0°C incubator to freeze for 1 hour. Then, add 13 g of lithium hexafluorophosphate while stirring. Finally, add 0.356 g of scavenger T1, 3.56 g of VC, 0.83 g of PS, and 0.95 g of LiPF2O2 and stir thoroughly.

[0047] The dry cell battery encapsulated using the above method is dried at 80-95℃ for 8-15h, then injected with electrolyte and placed in an environment of 25℃ for 48 hours. After the electrolyte has fully infiltrated the battery, pre-charge formation and capacity division are started. The pre-charge process is to charge to 10% SOC at a constant current of 0.01C, and then change to charging to 30% SOC at a constant current of 0.02C. After pre-charge, age for 48 hours at 45℃ and then vacuum pump. After aging, charge to 4.05V at a constant current and constant voltage of 0.01C, stand for 10 minutes, vacuum seal, and then discharge to 2.5V to determine the initial charge and discharge efficiency. Then continue aging at 45℃ for 24 hours. After aging, charge to 3.65V at a constant current and constant voltage of 0.1C and discharge to 2.5V at a constant current and constant voltage of 0.1C to obtain the finished lithium-ion battery.

[0048] Example 2

[0049] Prepare electrolyte:

[0050] Control the moisture content in the glove box to below 10 ppm, and the moisture content in the organic solvent to below 10 ppm. Using a percentile balance, accurately weigh 30 g of ethylene carbonate, 40 g of ethyl methyl carbonate, and 30 g of dimethyl carbonate into an aluminum bottle. Stir thoroughly and place in a 0°C incubator on ice for 1 hour. Then, add 13 g of lithium hexafluorophosphate while stirring. Finally, add 1.196 g of T1 reagent, 3.587 g of VC, 0.837 g of PS, and 0.957 g of LiPF2O2 and stir thoroughly.

[0051] The dry cell battery encapsulated using the above method is dried at 80-95℃ for 8-15h, then injected with electrolyte and placed in an environment of 25℃ for 48 hours. After the electrolyte has fully infiltrated the battery, pre-charge formation and capacity division are started. The pre-charge process is to charge to 10% SOC at a constant current of 0.01C, and then change to charging to 30% SOC at a constant current of 0.02C. After pre-charge, age for 48 hours at 45℃ and then vacuum pump. After aging, charge to 4.05V at a constant current and constant voltage of 0.01C, stand for 10 minutes, vacuum seal, and then discharge to 2.5V to determine the initial charge and discharge efficiency. Then continue aging at 45℃ for 24 hours. After aging, charge to 3.65V at a constant current and constant voltage of 0.1C and discharge to 2.5V at a constant current and constant voltage of 0.1C to obtain the finished lithium-ion battery.

[0052] Example 3

[0053] Prepare electrolyte:

[0054] Control the moisture content in the glove box to below 10 ppm, and the moisture content in the organic solvent to below 10 ppm. Using a percentile balance, accurately weigh 30 g of ethylene carbonate, 40 g of ethyl methyl carbonate, and 30 g of dimethyl carbonate into an aluminum bottle. Stir thoroughly and place in a 0°C incubator on ice for 1 hour. Then, add 13 g of lithium hexafluorophosphate while stirring. Finally, add 6.243 g of T1 reagent, 3.746 g of VC, 0.874 g of PS, and 0.999 g of LiPF2O2 and stir thoroughly.

[0055] The dry cell battery encapsulated using the above method is dried at 80-95℃ for 8-15h, then injected with electrolyte and placed in an environment of 25℃ for 48 hours. After the electrolyte has fully infiltrated the battery, pre-charge formation and capacity division are started. The pre-charge process is to charge to 10% SOC at a constant current of 0.01C, and then change to charging to 30% SOC at a constant current of 0.02C. After pre-charge, age for 48 hours at 45℃ and then vacuum pump. After aging, charge to 4.05V at a constant current and constant voltage of 0.01C, stand for 10 minutes, vacuum seal, and then discharge to 2.5V to determine the initial charge and discharge efficiency. Then continue aging at 45℃ for 24 hours. After aging, charge to 3.65V at a constant current and constant voltage of 0.1C and discharge to 2.5V at a constant current and constant voltage of 0.1C to obtain the finished lithium-ion battery.

[0056] Example 4

[0057] Prepare electrolyte:

[0058] Control the moisture content in the glove box to below 10 ppm, and the moisture content in the organic solvent to below 10 ppm. Using a percentile balance, accurately weigh 30 g of ethylene carbonate, 40 g of ethyl methyl carbonate, and 30 g of dimethyl carbonate into an aluminum bottle. Stir thoroughly and place in a 0°C incubator to freeze for 1 hour. Then, add 13 g of lithium hexafluorophosphate while stirring. Finally, add 0.356 g of T2 reagent, 3.56 g of VC, 0.83 g of PS, and 0.95 g of LiPF2O2 and stir thoroughly.

[0059] The dry cell battery encapsulated using the above method is dried at 80-95℃ for 8-15h, then injected with electrolyte and placed in an environment of 25℃ for 48 hours. After the electrolyte has fully infiltrated the battery, pre-charge formation and capacity division are started. The pre-charge process is to charge to 10% SOC at a constant current of 0.01C, and then change to charging to 30% SOC at a constant current of 0.02C. After pre-charge, age for 48 hours at 45℃ and then vacuum pump. After aging, charge to 4.05V at a constant current and constant voltage of 0.01C, stand for 10 minutes, vacuum seal, and then discharge to 2.5V to determine the initial charge and discharge efficiency. Then continue aging at 45℃ for 24 hours. After aging, charge to 3.65V at a constant current and constant voltage of 0.1C and discharge to 2.5V at a constant current and constant voltage of 0.1C to obtain the finished lithium-ion battery.

[0060] Example 5

[0061] Prepare electrolyte:

[0062] Control the moisture content in the glove box to below 10 ppm, and the moisture content in the organic solvent to below 10 ppm. Using a percentile balance, accurately weigh 30 g of ethylene carbonate, 40 g of ethyl methyl carbonate, and 30 g of dimethyl carbonate into an aluminum bottle. Stir thoroughly and place in a 0°C incubator on ice for 1 hour. Then, add 13 g of lithium hexafluorophosphate while stirring. Finally, add 1.196 g of T2 reagent, 3.587 g of VC, 0.837 g of PS, and 0.957 g of LiPF2O2 and stir thoroughly.

[0063] The dry cell battery encapsulated using the above method is dried at 80-95℃ for 8-15h, then injected with electrolyte and placed in an environment of 25℃ for 48 hours. After the electrolyte has fully infiltrated the battery, pre-charge formation and capacity division are started. The pre-charge process is to charge to 10% SOC at a constant current of 0.01C, and then change to charging to 30% SOC at a constant current of 0.02C. After pre-charge, age for 48 hours at 45℃ and then vacuum pump. After aging, charge to 4.05V at a constant current and constant voltage of 0.01C, stand for 10 minutes, vacuum seal, and then discharge to 2.5V to determine the initial charge and discharge efficiency. Then continue aging at 45℃ for 24 hours. After aging, charge to 3.65V at a constant current and constant voltage of 0.1C and discharge to 2.5V at a constant current and constant voltage of 0.1C to obtain the finished lithium-ion battery.

[0064] Example 6

[0065] Prepare electrolyte:

[0066] Control the moisture content in the glove box to below 10 ppm, and the moisture content in the organic solvent to below 10 ppm. Using a percentile balance, accurately weigh 30 g of ethylene carbonate, 40 g of ethyl methyl carbonate, and 30 g of dimethyl carbonate into an aluminum bottle. Stir thoroughly and place in a 0°C incubator on ice for 1 hour. Then, add 13 g of lithium hexafluorophosphate while stirring. Finally, add 6.243 g of T2 reagent, 3.746 g of VC, 0.874 g of PS, and 0.999 g of LiPF2O2 and stir thoroughly.

[0067] The dry cell battery encapsulated using the above method is dried at 80-95℃ for 8-15h, then injected with electrolyte and placed in an environment of 25℃ for 48 hours. After the electrolyte has fully infiltrated the battery, pre-charge formation and capacity division are started. The pre-charge process is to charge to 10% SOC at a constant current of 0.01C, and then change to charging to 30% SOC at a constant current of 0.02C. After pre-charge, age for 48 hours at 45℃ and then vacuum pump. After aging, charge to 4.05V at a constant current and constant voltage of 0.01C, stand for 10 minutes, vacuum seal, and then discharge to 2.5V to determine the initial charge and discharge efficiency. Then continue aging at 45℃ for 24 hours. After aging, charge to 3.65V at a constant current and constant voltage of 0.1C and discharge to 2.5V at a constant current and constant voltage of 0.1C to obtain the finished lithium-ion battery.

[0068] Example 7

[0069] Prepare electrolyte:

[0070] Control the moisture content in the glove box to below 10 ppm, and the moisture content in the solvent to below 10 ppm. Using a percentile balance, accurately weigh 30 g of ethylene carbonate, 40 g of ethyl methyl carbonate, and 30 g of dimethyl carbonate into an aluminum bottle. Stir thoroughly and place in a 0°C incubator to freeze for 1 hour. Then, add 13 g of lithium hexafluorophosphate while stirring. Finally, add 0.356 g of T3 reagent, 3.56 g of VC, 0.83 g of PS, and 0.95 g of LiPF2O2 and stir thoroughly.

[0071] The dry cell battery encapsulated using the above method is dried at 80-95℃ for 8-15h, then injected with electrolyte and placed in an environment of 25℃ for 48 hours. After the electrolyte has fully infiltrated the battery, pre-charge formation and capacity division are started. The pre-charge process is to charge to 10% SOC at a constant current of 0.01C, and then change to charging to 30% SOC at a constant current of 0.02C. After pre-charge, age for 48 hours at 45℃ and then vacuum pump. After aging, charge to 4.05V at a constant current and constant voltage of 0.01C, stand for 10 minutes, vacuum seal, and then discharge to 2.5V to determine the initial charge and discharge efficiency. Then continue aging at 45℃ for 24 hours. After aging, charge to 3.65V at a constant current and constant voltage of 0.1C and discharge to 2.5V at a constant current and constant voltage of 0.1C to obtain the finished lithium-ion battery.

[0072] Example 8

[0073] Prepare electrolyte:

[0074] Control the moisture content in the glove box to below 10 ppm, and the moisture content in the solvent to below 10 ppm. Using a percentile balance, accurately weigh 30 g of ethylene carbonate, 40 g of ethyl methyl carbonate, and 30 g of dimethyl carbonate into an aluminum bottle. Stir thoroughly and place in a 0°C incubator on ice for 1 hour. Then, add 13 g of lithium hexafluorophosphate while stirring. Finally, add 1.196 g of T3 reagent, 3.587 g of VC, 0.837 g of PS, and 0.957 g of LiPF2O2 and stir thoroughly.

[0075] The dry cell battery encapsulated using the above method is dried at 80-95℃ for 8-15h, then injected with electrolyte and placed in an environment of 25℃ for 48 hours. After the electrolyte has fully infiltrated the battery, pre-charge formation and capacity division are started. The pre-charge process is to charge to 10% SOC at a constant current of 0.01C, and then change to charging to 30% SOC at a constant current of 0.02C. After pre-charge, age for 48 hours at 45℃ and then vacuum pump. After aging, charge to 4.05V at a constant current and constant voltage of 0.01C, stand for 10 minutes, vacuum seal, and then discharge to 2.5V to determine the initial charge and discharge efficiency. Then continue aging at 45℃ for 24 hours. After aging, charge to 3.65V at a constant current and constant voltage of 0.1C and discharge to 2.5V at a constant current and constant voltage of 0.1C to obtain the finished lithium-ion battery.

[0076] Example 9

[0077] Prepare electrolyte:

[0078] Control the moisture content in the glove box to below 10 ppm, and the moisture content in the solvent to below 10 ppm. Using a percentile balance, accurately weigh 30 g of ethylene carbonate, 40 g of ethyl methyl carbonate, and 30 g of dimethyl carbonate into an aluminum bottle. Stir thoroughly and place in a 0°C incubator on ice for 1 hour. Then, add 13 g of lithium hexafluorophosphate while stirring. Finally, add 6.243 g of T3 reagent, 3.746 g of VC, 0.874 g of PS, and 0.999 g of LiPF2O2 and stir thoroughly.

[0079] The dry cell battery encapsulated using the above method is dried at 80-95℃ for 8-15h, then injected with electrolyte and placed in an environment of 25℃ for 48 hours. After the electrolyte has fully infiltrated the battery, pre-charge formation and capacity division are started. The pre-charge process is to charge to 10% SOC at a constant current of 0.01C, and then change to charging to 30% SOC at a constant current of 0.02C. After pre-charge, age for 48 hours at 45℃ and then vacuum pump. After aging, charge to 4.05V at a constant current and constant voltage of 0.01C, stand for 10 minutes, vacuum seal, and then discharge to 2.5V to determine the initial charge and discharge efficiency. Then continue aging at 45℃ for 24 hours. After aging, charge to 3.65V at a constant current and constant voltage of 0.1C and discharge to 2.5V at a constant current and constant voltage of 0.1C to obtain the finished lithium-ion battery.

[0080] Comparative Example

[0081] Prepare electrolyte:

[0082] Control the moisture content in the glove box to below 10 ppm, and the moisture content in the solvent to below 10 ppm. Using a percentile balance, accurately weigh 30 g of ethylene carbonate, 40 g of ethyl methyl carbonate, and 30 g of dimethyl carbonate into an aluminum bottle. Stir thoroughly and place in a 0°C incubator to freeze for 1 hour. Then, add 13 g of lithium hexafluorophosphate while stirring. Finally, add 3.550 g of VC, 0.828 g of PS, and 0.947 g of LiPF2O2 and stir thoroughly.

[0083] The dry cell battery encapsulated using the above method is dried at 80-95℃ for 8-15h, then injected with electrolyte and placed in an environment of 25℃ for 48 hours. After the electrolyte has fully infiltrated the battery, pre-charge formation and capacity division are started. The pre-charge process is to charge to 10% SOC at a constant current of 0.01C, and then change to charging to 30% SOC at a constant current of 0.02C. After pre-charge, age for 48 hours at 45℃ and then vacuum pump. After aging, charge to 4.05V at a constant current and constant voltage of 0.01C, stand for 10 minutes, vacuum seal, and then discharge to 2.5V to determine the initial charge and discharge efficiency. Then continue aging at 45℃ for 24 hours. After aging, charge to 3.65V at a constant current and constant voltage of 0.1C and discharge to 2.5V at a constant current and constant voltage of 0.1C to obtain the finished lithium-ion battery.

[0084] Performance testing:

[0085] The electrolytes and lithium-ion batteries of the examples and comparative examples were tested and compared using the following methods:

[0086] (1) Lithium-ion battery 45°C cycle test

[0087] The lithium-ion batteries assembled in the embodiment and comparative example were subjected to a 45°C cycle test according to the following steps. The specific steps are: take a lithium-ion battery that has been fixed in volume, measure the volume of the lithium-ion battery, and then place it in a 45°C constant temperature box and let it stand for more than 1 hour to ensure that the internal temperature of the battery is close to 45°C. Then charge it at a constant current and constant voltage of 1C, with a cut-off voltage of 3.65V and a cut-off current of 0.05C. Then discharge it to 2.5V at a constant current of 1C. Perform charge and discharge cycles on the battery according to the above steps, and record the discharge capacity retention rate and volume change rate after 1000 cycles. The discharge capacity retention rate of the battery after 1000 cycles is calculated as the discharge capacity after the cycle divided by the discharge capacity of the first cycle. Specific test data are shown in Table 1.

[0088] Table 1 45°C cycle performance test results of lithium-ion batteries of the embodiment and comparative example

[0089]

[0090] As shown in Table 1, the gas production phenomenon of the battery cells during cycling was significantly improved after the addition of deoxidizers in Examples 1-5. As the deoxidizer content increased, the volume change rate also decreased, indicating that the higher the deoxidizer content, the lower the gas production. The amount of deoxidizers T1, T2, and T3 added has a certain effect on the capacity retention rate of the lithium-ion battery during high-temperature cycling, and the capacity retention rate first increases and then decreases with the increase of the deoxidizer content. Among the three deoxidizers, T1 has the highest capacity retention rate, and its ability to inhibit gas production is close to that of T2, slightly worse than T3, but T3 has the worst capacity retention rate. T1 was comprehensively selected as the best deoxidizer. The capacity retention rate is optimal when 1% T1 is added, and the volume change rate is low. Further increasing the amount of T1 added significantly worsens the capacity retention rate, so the optimal addition amount of T1 is 1%.

[0091] (2) Lithium-ion battery rate test at 25°C

[0092] The batteries in the examples and comparative examples were tested for rate performance at 25° C. according to the following steps.

[0093] The specific operation steps are as follows: Place the battery in a constant temperature cabinet at 25°C and let it sit for 6 hours before starting charging and discharging. First, charge at a constant current and constant voltage of 0.1C and discharge at a constant current of 0.1C to constant capacity. Then, vary the discharge rate: discharge the battery to 2.5V at 0.3C, 0.5C, and 1C, respectively. The discharge capacity at each rate is calculated. Divide the discharge capacity at each rate by the discharge capacity at 0.1C to obtain the capacity retention rate at each rate. The test results at the 25°C rate are shown in Table 2.

[0094] Table 2 25°C rate test results of lithium-ion batteries of the embodiment and comparative example

[0095]

[0096] As shown in Table 2, both T2 and T3 oxygen scavengers degrade the rate performance of lithium-ion batteries within the 0.5-5% addition range, and the degradation becomes more pronounced as the addition level increases. T1 has almost no effect on the rate performance of lithium-ion batteries within the 0.3-1% range, but when the T1 addition level reaches 5%, the degradation significantly increases. The data shows that 1% T1 provides the best rate performance.

[0097] (3) Lithium-ion battery storage test at 60°C

[0098] The lithium-ion batteries in the examples and comparative examples were subjected to a high-temperature storage performance test. The specific steps are as follows: the fixed-capacity battery was discharged to 2.5V at a constant current of 1C, left for 5 minutes, and then charged to 3.65V at a constant current and constant voltage of 1C, with a cut-off current of 0.05C. The volume of the battery cell was measured, and then the battery was placed in a constant temperature box at 60°C and stored for 30 days, 60 days, 90 days, 120 days, and 150 days respectively. After the battery was stored to the specified date, the battery was taken out and the volume of the battery cell was measured. The battery with measured volume was connected to a test cabinet, discharged to 2.5V at a constant current of 1C, and then charged at a constant current and constant voltage of 1C. The process of 1C constant current discharge was repeated 3 times. Finally, the discharge capacity recovery rate of the battery was obtained. The relevant test results are shown in Table 3.

[0099] Table 3. 60°C storage test results of lithium-ion batteries of the embodiment and comparative example

[0100]

[0101] As shown in Table 3, the effects of deoxidizer type and addition amount on the capacity recovery rate of lithium-ion batteries during high-temperature storage are compared. The capacity recovery rate of T1 is better than that of T3, the capacity recovery rate of T3 is better than that of T2, and 1% T1 is better than 0.3% T1 and 5% T1. The capacity recovery rates of 0.3% T1 (Example 1) and 1% T1 (Example 2) are higher than those of the control example, while the other examples are worse than the control example. Comparing the gas production during high-temperature storage, all examples are better than the control example, and the higher the deoxidizer content, the lower the gas production. Among T1, T2 and T3, T2 has the best effect in inhibiting gas production. Combining the capacity recovery rate and volume change rate, the example with 1% T1 has the most balanced effect.

[0102] Combining the data of 45℃ cycling, room temperature rate data, and high temperature storage, it was determined that T1 scavenger has the most balanced performance in all aspects, and adding 1% T1 scavenger to the electrolyte has the best effect.

[0103] The above-described embodiments merely illustrate several implementations of the present invention, and while their descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that a person skilled in the art would be able to make numerous variations and improvements without departing from the spirit of the present invention, all of which fall within the scope of protection of the present invention. Therefore, the scope of protection of the present invention shall be determined by the appended claims.

Claims

1. An electrolyte capable of inhibiting gas production from lithium-rich lithium ferrite, characterized in that: The method comprises a lithium salt, an organic solvent, and an additive, wherein the additive comprises an oxygen scavenger, and the oxygen scavenger has a structural formula (I): （I）； Wherein, R1 is selected from one of an alkyl group having 1 to 12 carbon atoms, an alkenyl group having 1 to 10 carbon atoms, an alkynyl group having 1 to 10 carbon atoms, a halogen substituent, a phenyl group, an aryl group, a heterocyclic group, an ether group, a cyano group, an azide group, a sulfur-containing group, a phosphorus-containing group, a silicon-containing group, a nitrogen-containing group, and a boron-containing group.

2. The electrolyte capable of inhibiting gas generation of lithium-rich lithium ferrite according to claim 1, characterized in that: R1 is selected from one of trifluoromethyl, phenyl and cyano.

3. The electrolyte capable of inhibiting gas generation of lithium-rich lithium ferrite according to claim 1, characterized in that: The content of the deoxidizer in the electrolyte is 0.3-5wt%.

4. The electrolyte capable of suppressing gas generation of lithium-rich lithium ferrite according to claim 1, characterized in that: R1 is selected from trifluoromethyl; the content of the oxygen scavenger in the electrolyte is 0.5-1wt%.

5. The electrolyte capable of inhibiting gas generation of lithium-rich lithium ferrite according to claim 1, characterized in that: The additives further include vinylene carbonate, 1,3-propane sultone, and lithium difluorophosphate.

6. The electrolyte capable of suppressing gas generation of lithium-rich lithium ferrite according to claim 5, characterized in that: The content of vinylene carbonate in the electrolyte is 0.3-10 wt %, the content of 1,3-propane sultone in the electrolyte is 0.3-5 wt %, and the content of lithium difluorophosphate in the electrolyte is 0.1-2 wt %.

7. The electrolyte capable of suppressing gas generation of lithium-rich lithium ferrite according to claim 1, characterized in that: The organic solvent includes ethylene carbonate, ethyl methyl carbonate, and dimethyl carbonate.

8. The electrolyte capable of suppressing gas generation of lithium-rich lithium ferrite according to claim 1, characterized in that: The mass ratio of ethylene carbonate, ethyl methyl carbonate and dimethyl carbonate in the organic solvent is 0.8-1.2:1-1.5:

1.

9. The electrolyte capable of suppressing gas generation of lithium-rich lithium ferrite according to claim 1, characterized in that: The lithium salt includes lithium hexafluorophosphate.

10. A lithium ion battery, characterized in that: The invention comprises a positive electrode sheet, a negative electrode sheet, a separator and an electrolyte as claimed in any one of claims 1 to 9; the positive electrode sheet comprises lithium-rich lithium ferrite.

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