Electrolyte, preparation method thereof, electrolyte injection method and lithium ion battery

Abstract

The invention relates to the technical field of lithium ion batteries, in particular to an electrolyte, a preparation method thereof, an injection method and a lithium ion battery, the electrolyte comprises a first electrolyte for first injection and a second electrolyte for second injection, the first electrolyte comprises a first solvent, a first lithium salt and a first additive, the second electrolyte comprises a second solvent, a second lithium salt and a second additive, the first electrolyte comprises a first solvent, a first lithium salt and a first additive, the second electrolyte comprises a second solvent, a second lithium salt and a second additive, the mass percentage of the second electrolyte in the electrolyte is 5-20%, the first additive comprises dimethyl sulfide and vinylene carbonate, and the second additive comprises triphenyl phosphate and vinylene carbonate. According to the electrolyte, the first additive comprises dimethyl sulfide, and the second additive comprises triphenyl phosphite, so that the bad problems of high-temperature gas production and negative electrode interface black spots in the use process of a lithium-rich material lithium supplementing agent are solved.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium ion batteries, and in particular to an electrolyte and a preparation method thereof, a liquid injection method and a lithium ion battery. Background Art

[0002] The current market has increasingly higher requirements for the cycle performance of secondary batteries, requiring high energy density, ultra-long service life, and slow decay in the early stage. When lithium iron phosphate is used as the positive electrode material, due to its low specific capacity and the reaction loss of lithium during the first charging process, the energy density is relatively low, and the cycle trend is often that the capacity loss is fast at first and then slow, which does not meet the market's requirements for slow decay in the early stage of the cycle. Positive electrode lithium replenishment technology is used in secondary batteries. At present, positive electrode lithium replenishment in lithium iron phosphate systems mostly adopts electrochemical methods to replenish lithium. Lithium-rich materials are added to the positive electrode materials. During the charging process, the lithium-rich materials complete the lithium removal and replenish lithium to the positive electrode, thereby increasing the battery energy density and improving the cycle life.

[0003] The general formula of lithium-rich materials is Li x M y O z (M is a transition metal element), which is added to the positive electrode. During the battery formation stage, the charging voltage needs to be set to a higher voltage of 3.7V or above under high temperature conditions to complete the release of lithium ions and release a certain amount of oxygen. At this time, the battery capacity and energy density are significantly improved. In order to improve the impact of oxygen released during lithium replenishment on battery performance, electrolytes often use additives containing sulfite and sulfonate to protect the positive electrode film and form a cross-linked negative electrode SEI to reduce damage to it by side reactions.

[0004] The existing electrolyte protects the negative electrode and the interface between the positive electrode and the electrolyte. However, under high temperature and high voltage, the damage caused by the oxygen free radicals released when the lithium-rich material decomposes is still serious: the organic solvent is oxidized to produce H2O, HF and other substances that are harmful to battery performance, resulting in more subsequent high-temperature side reactions of the battery, resulting in gas production and black spots on the negative electrode interface, thus affecting the storage life and cycle life of the battery.

[0005] Therefore, how to provide an electrolyte that can improve the undesirable problems of high-temperature gas generation and black spots on the negative electrode interface during the use of lithium-rich material lithium supplements is a technical problem that needs to be solved urgently in this field. Summary of the invention

[0006] In view of the above-mentioned deficiencies in the prior art, the object of the present invention is to provide an electrolyte and a preparation method thereof, an injection method and a lithium-ion battery. The electrolyte improves the problems of high-temperature gas production and black spots on the negative electrode interface during the use of lithium-rich material lithium supplements by including dimethyl sulfide (DMS) in the first additive and triphenyl phosphite (Tppi) in the second additive.

[0007] In order to achieve the above object, the present invention adopts the following technical solutions:

[0008] In a first aspect, the present invention provides an electrolyte, comprising a first electrolyte for a first injection and a second electrolyte for a second injection, wherein the first electrolyte comprises a first solvent, a first lithium salt and a first additive, and the second electrolyte comprises a second solvent, a second lithium salt and a second additive, wherein the mass percentage of the second electrolyte to the electrolyte is 5% to 20%, the first additive comprises dimethyl sulfide and vinylene carbonate, and the second additive comprises triphenyl phosphite and vinylene carbonate.

[0009] The electrolyte includes dimethyl sulfide (DMS) in the first additive and triphenyl phosphite (Tppi) in the second additive, thereby improving the undesirable problems of high-temperature gas generation and black spots on the negative electrode interface during the use of lithium-rich material lithium supplement.

[0010] Further, the first solvent includes at least two of dimethyl carbonate, ethyl methyl carbonate, ethylene carbonate, propylene carbonate, diethyl carbonate, ethyl formate, and ethyl propionate;

[0011] and / or, in the first solvent, the weight ratio between every two compounds is (2-5):(2-5);

[0012] And / or, the first lithium salt includes at least one of lithium hexafluorophosphate and lithium bis(fluorosulfonyl)imide;

[0013] And / or, based on the total mass of the first electrolyte being 100%, the mass proportion of the first solvent in the first electrolyte is 75-90%, the mass proportion of the first lithium salt in the first electrolyte is 7%-20%, and the mass proportion of the first additive in the first electrolyte is 0.3%-7%.

[0014] Further, the first additive also includes at least one of methylene disulfonate, lithium difluorophosphate, fluoroethylene carbonate, vinyl sulfate, 1,3-propane sultone, tris(trimethylsilane)phosphate, lithium difluorooxalatoborate, and difluorooxalatophosphate;

[0015] And / or, the mass percentage of dimethyl sulfide in the first electrolyte is 0.1-3wt%;

[0016] And / or, the mass percentage of vinylene carbonate in the first additive to the first electrolyte is not higher than 2%.

[0017] Further, the second solvent includes at least two of dimethyl carbonate, ethyl methyl carbonate, ethylene carbonate, propylene carbonate, diethyl carbonate, ethyl formate, and ethyl propionate;

[0018] and / or, in the second solvent, the weight ratio between each two compounds is (2-5):(2-5);

[0019] and / or, the second lithium salt comprises at least one of lithium hexafluorophosphate and lithium bis(fluorosulfonyl)imide;

[0020] And / or, based on the total mass of the second electrolyte as 100%, the mass proportion of the second solvent in the second electrolyte is 52% to 82%, the mass proportion of the second lithium salt in the second electrolyte is 7% to 18%, and the mass proportion of the second additive in the second electrolyte is 10.01% to 30.5%.

[0021] Further, the mass percentage of vinylene carbonate in the second additive in the second electrolyte is greater than the mass percentage of vinylene carbonate in the first additive in the first electrolyte;

[0022] And / or, the mass percentage of triphenyl phosphite in the second electrolyte is 0.01-0.5%;

[0023] And / or, the mass percentage of vinylene carbonate in the second additive to the second electrolyte is 10% to 30%.

[0024] In a second aspect, the present invention provides a method for preparing the electrolyte according to the first aspect, the preparation method comprising the following steps:

[0025] Weighing each component according to the designed ratio, and mixing the weighed first solvent and the first lithium salt uniformly to obtain a first primary electrolyte; adding the first additive to the first primary electrolyte, and mixing uniformly to obtain the first electrolyte;

[0026] Weigh each component according to the designed ratio, mix the weighed second solvent and the second lithium salt evenly to obtain a second primary electrolyte; add the second additive to the second primary electrolyte, mix evenly, and obtain the second electrolyte.

[0027] In a third aspect, the present invention provides a method for injecting an electrolyte as described in the first aspect, the method comprising the following steps:

[0028] The first electrolyte is injected into the battery to be filled and sealed. After sufficient infiltration, the formation and overcharge lithium replenishment processes are carried out. Then the second electrolyte is injected and sealed. After sufficient infiltration again, the electrolytes are mixed and the capacity-divided charging process is carried out.

[0029] Furthermore, the sufficient infiltration includes standing at 20 to 60° C. for 12 to 36 hours.

[0030] In a fourth aspect, the present invention provides a lithium-ion battery, wherein the lithium-ion battery comprises the electrolyte described in the first aspect, or is prepared by the injection method described in the third aspect.

[0031] Furthermore, the lithium-ion battery further comprises a positive electrode sheet, a negative electrode sheet and a separator, wherein the positive electrode sheet comprises a positive current collector and a positive active film layer, wherein the positive active film layer comprises a lithium replenisher, and the general chemical formula of the lithium replenisher is Li x M y O z , where M represents a transition metal, 1≤x≤6, 1≤y≤2, 2≤z≤4;

[0032] And / or, the lithium supplement includes at least one of lithium nickel oxide, lithium ferrite, and lithium oxide.

[0033] Compared with the prior art, the beneficial effects of the present invention include at least one of the following:

[0034] (1) The electrolyte provided by the present invention improves the problems of high-temperature gas generation and black spots on the negative electrode interface during the use of lithium-rich material lithium supplements by including dimethyl sulfide (DMS) in the first additive and triphenyl phosphite (Tppi) in the second additive.

[0035] (2) The electrolyte formula provided by the present invention adds DMS to the first electrolyte to absorb and prevent the influence of oxygen free radicals released by the lithium supplement additive during the reaction process on the positive and negative electrodes, and at the same time uses a small amount of VC to participate in film formation, so that the residual amount of VC after formation is small, and the oxidation of VC at high voltage is reduced; Tppi is added to the second electrolyte to annihilate the oxidizing components generated by part of the lithium supplement additive that has not been completely decomposed, and to capture the oxygen that escapes and remains in the battery during the decomposition process, and converts itself into a more pressure-resistant phosphate ester, which can reduce the influence of oxygen on the graphite negative electrode and increase the high-voltage stability of the battery positive electrode. The amount of VC used in the second composition system is higher than that in the first system, which is to supplement the VC content in the electrolyte and ensure that there is a sufficient amount of film-forming additives for the repair of SEI during the later cycle and storage process; thus, the combination can effectively improve the high-temperature gas generation problem of the lithium supplement system and ensure the battery cycle stability after lithium supplementation. DETAILED DESCRIPTION

[0036] In order to make the purpose, technical scheme and advantages of the present invention clearer, the technical scheme in the embodiment of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. It should be understood by those skilled in the art that the embodiments are only to help understand the present invention and should not be regarded as specific limitations of the present invention. Based on the embodiments in the present invention, all other embodiments obtained by ordinary technicians in the field without making creative work are within the scope of protection of the present invention. The process parameters of the following embodiments that do not specify specific conditions are usually based on conventional conditions.

[0037] The endpoints and any values ​​of the ranges disclosed in the present invention are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of each range, the endpoint values ​​of each range and the individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be regarded as specifically disclosed in the present invention.

[0038] In a first aspect, the present invention provides an electrolyte, comprising a first electrolyte for a first injection and a second electrolyte for a second injection, wherein the first electrolyte comprises a first solvent, a first lithium salt and a first additive, and the second electrolyte comprises a second solvent, a second lithium salt and a second additive, wherein the mass percentage of the second electrolyte to the electrolyte is 5% to 20%, for example, it can be 5%, 10%, 15% or 20%, the first additive comprises dimethyl sulfide (DMS) and vinylene carbonate (VC), and the second additive comprises triphenyl phosphite (Tppi) and vinylene carbonate (VC).

[0039] The electron donor groups in dimethyl sulfide can combine with oxygen free radicals generated by the decomposition of the lithium supplement agent and generate a structurally stable positive electrode S-containing solid electrolyte membrane, which inactivates oxygen free radicals at the beginning of their generation and prevents them from escaping, thereby reducing the negative effects caused by the highly oxidizing oxygen.

[0040] By utilizing the unsaturated functional groups in triphenyl phosphite (Tppi) to combine with oxygen free radicals, it is possible to annihilate some of the oxidizing components produced by the undecomposed lithium-supplementing additives, capture the oxygen that escapes during the formation process and remains in the battery, and convert itself into a more pressure-resistant phosphate ester, which can not only reduce the impact of oxygen on the graphite negative electrode, but also increase the high-voltage stability of the battery positive electrode, thereby improving the high-voltage performance of the battery.

[0041] By including vinylene carbonate (VC), VC can better form a SEI film in a lithium iron phosphate battery system, thereby isolating the contact between the electrolyte and the active material and reducing the decomposition of the electrolyte.

[0042] The present invention can provide a possible electrolyte solution for the lithium replenishment system, improve the undesirable problems such as high-temperature gas generation, interface black spots, and pole piece peeling during the use of the current lithium replenisher, thereby improving the cycle life and calendar storage life of the battery.

[0043] The electrolyte provided by the present invention includes dimethyl sulfide in the first additive and triphenyl phosphite in the second additive, thereby improving the undesirable problems of high-temperature gas production, black spots on the negative electrode interface, and pole piece delamination (powder loss) during the use of lithium-rich material lithium supplement agents, thereby improving the cycle life and calendar storage life of lithium-ion batteries.

[0044] In the above electrolyte, as an optional implementation, the mass ratio of the first electrolyte to the second electrolyte is (80-95):(5-20), for example, it can be 80:20, 85:15, 90:10 or 95:5.

[0045] In the above-mentioned electrolyte, as an optional embodiment, the first solvent includes at least two of dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), ethylene carbonate (EC), propylene carbonate, diethyl carbonate (DEC), ethyl formate (EA), and ethyl propionate (EP).

[0046] In the above electrolyte, as an optional embodiment, in the first solvent, the weight ratio between every two compounds is (2-5): (2-5), for example, it can be 3:4, 3:3 or 2:5.

[0047] In the above electrolyte, as an optional embodiment, the first solvent includes dimethyl carbonate (DMC), ethyl methyl carbonate (EMC) and ethylene carbonate (EC), and the mass ratio of the DMC, EMC and EC is (2-5): (2-5): (2-5).

[0048] In the above electrolyte, as an optional implementation, the first lithium salt includes at least one of lithium hexafluorophosphate and lithium bis(fluorosulfonyl)imide.

[0049] In the above electrolyte, as an optional embodiment, the first lithium salt includes lithium hexafluorophosphate and lithium bis(fluorosulfonyl)imide, and the mass ratio of the lithium hexafluorophosphate to the lithium bis(fluorosulfonyl)imide is 10:(0.5-10), for example, it can be 10:0.5, 10:1, 10:3, 10:5, 10:7 or 10:10.

[0050] In the above-mentioned electrolyte, as an optional embodiment, based on the total mass of the first electrolyte as 100%, the mass proportion of the first solvent in the first electrolyte is 75-90% (for example, it can be 75%, 80% or 90%), the mass proportion of the first lithium salt in the first electrolyte is 7%-20% (for example, it can be 7%, 11%, 13%, 15% or 20%), and the mass proportion of the first additive in the first electrolyte is 0.3%-7% (for example, it can be 0.3%, 1%, 3%, 5% or 7%).

[0051] In the above-mentioned electrolyte, as an optional embodiment, the first additive also includes at least one of methylene disulfonate MMDS, lithium difluorophosphate LiPO2F2, fluoroethylene carbonate FEC, vinyl sulfate DTD, 1,3-propane sultone PS, tris(trimethylsilane) phosphate TMSP, lithium difluorooxalatoborate LiDFOB, and difluorooxalatophosphate LiDFOP.

[0052] In the above electrolyte, as an optional implementation, the first additive also includes fluoroethylene carbonate FEC and vinyl sulfate DTD, and the mass ratio of the fluoroethylene carbonate to the vinyl sulfate is (0.5-1.5):1.

[0053] In the above-mentioned electrolyte, as an optional embodiment, the mass percentage of dimethyl sulfide (DMS) in the first electrolyte is 0.1 to 3wt%, for example, it can be 0.1wt%, 0.5wt%, 1wt%, 1.5wt%, 2wt%, 2.5wt% or 3wt%; when the content is too high, it will cause the system impedance to be too large, affecting the kinetic performance, and when the content is low, the effect is difficult to manifest.

[0054] VC has weak oxidation resistance and is easily involved in reaction decomposition under high voltage and high oxidizing environment, resulting in more gas production, causing black spots on the negative electrode interface of the battery, and even lithium precipitation. Therefore, in the above-mentioned electrolyte, as a preferred embodiment, the mass percentage of vinylene carbonate (VC) in the first additive in the first electrolyte is not higher than 2%. After formation and before the decomposition of the lithium supplement material, reducing the free VC in the electrolyte can reduce its negative effects after oxidation. More preferably, a better performance is achieved when the VC is selected at 1% to 2%.

[0055] In the above-mentioned electrolyte, as an optional embodiment, the second solvent includes at least two of dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), ethylene carbonate (EC), propylene carbonate, diethyl carbonate (DEC), ethyl formate (EA), and ethyl propionate (EP).

[0056] In the above electrolyte, as an optional embodiment, in the second solvent, the weight ratio between every two compounds is (2-5): (2-5), for example, it can be 3:4, 3:3 or 2:5.

[0057] In the above electrolyte, as an optional embodiment, the second solvent includes dimethyl carbonate (DMC), ethyl methyl carbonate (EMC) and ethylene carbonate (EC), and the mass ratio of the DMC, EMC and EC is (2-5): (2-5): (2-5).

[0058] In the above electrolyte, as an optional implementation, the second lithium salt includes at least one of lithium hexafluorophosphate and lithium bis(fluorosulfonyl)imide.

[0059] In the above electrolyte, as an optional embodiment, the second lithium salt includes lithium hexafluorophosphate and lithium bis(fluorosulfonyl)imide, and the mass ratio of the lithium hexafluorophosphate to the lithium bis(fluorosulfonyl)imide is 10:(0.5-10), for example, it can be 10:0.5, 10:1, 10:3, 10:5, 10:7 or 10:10.

[0060] In the above-mentioned electrolyte, as an optional embodiment, based on the total mass of the second electrolyte as 100%, the mass proportion of the second solvent in the second electrolyte is 52% to 82% (for example, it can be 52%, 54%, 58%, 60%, 70%, 80% or 82%), the mass proportion of the second lithium salt in the second electrolyte is 7%-18% (for example, it can be 7%, 11%, 13%, 15% or 18%), and the mass proportion of the second additive in the second electrolyte is 10.01% to 30.5% (for example, it can be 10.01%, 15%, 20%, 25% or 30.5%).

[0061] In the above electrolyte, as an optional implementation, the mass percentage of vinylene carbonate in the second additive in the second electrolyte is greater than the mass percentage of vinylene carbonate in the first additive in the first electrolyte.

[0062] By making the mass percentage of vinylene carbonate in the second additive in the second electrolyte greater than the mass percentage of vinylene carbonate in the first additive in the first electrolyte, the VC content in the electrolyte can be supplemented to ensure that there is a sufficient amount of film-forming additive for repairing SEI during later cycles and storage.

[0063] In the above electrolyte, as an optional implementation, the mass percentage of triphenyl phosphite (Tppi) in the second electrolyte is 0.01-0.5%, for example, it can be 0.01%, 0.1%, 0.3% or 0.5%; when the content is too high, the overall impedance is too large, which has a negative impact on the first effect and capacity of the battery.

[0064] In the above electrolyte, as an optional embodiment, the mass percentage of vinylene carbonate (VC) in the second additive in the second electrolyte is 10% to 30%, for example, it can be 10%, 15%, 20% or 30%. If the content of vinylene carbonate (VC) in the second electrolyte is too low, the cycle life is poor and the storage performance is poor; if the content of vinylene carbonate (VC) in the second electrolyte is too high, the impedance is large, which may cause lithium precipitation and poor performance.

[0065] In a second aspect, the present invention provides a method for preparing the electrolyte according to the first aspect, the preparation method comprising the following steps:

[0066] Weighing each component according to the designed ratio, and mixing the weighed first solvent and the first lithium salt uniformly to obtain a first primary electrolyte; adding the first additive to the first primary electrolyte, and mixing uniformly to obtain the first electrolyte;

[0067] Weigh each component according to the designed ratio, mix the weighed second solvent and the second lithium salt evenly to obtain a second primary electrolyte; add the second additive to the second primary electrolyte, mix evenly, and obtain the second electrolyte.

[0068] In a third aspect, the present invention provides a method for injecting an electrolyte as described in the first aspect, comprising the following steps:

[0069] The first electrolyte is injected into the battery to be filled and sealed. After sufficient infiltration, the formation and overcharge lithium replenishment processes are carried out. Then the second electrolyte is injected and sealed. After sufficient infiltration again, the electrolytes are mixed and the capacity-divided charging process is carried out.

[0070] In the above-mentioned electrolyte injection method, as an optional embodiment, the sufficient infiltration includes standing at 20-60°C (for example, it can be 20°C, 30°C, 40°C, 50°C or 60°C) for 12-36h (for example, it can be 12h, 18h, 24h, 30h or 36h).

[0071] In the above-mentioned electrolyte injection method, as an optional implementation, the formation process includes charging at 45°C at a constant current of 0.1C for 7 minutes, and then charging at a constant current of 0.2C for 120 minutes; the overcharge lithium replenishment process includes charging at 45°C at a constant current of 0.5C to 3.65V, and then charging at a constant current of 0.2C to 4.2-4.3V; the differentiated capacity charging process includes discharging at room temperature at a constant current of 0.5C to 2.5V, then charging at a constant current of 0.5C to 3.65V, standing for 10 minutes, then discharging at a constant current of 0.5C to 2.5V, and charging at a constant current of 1C for 12 minutes.

[0072] In a fourth aspect, the present invention provides a lithium-ion battery, wherein the lithium-ion battery comprises the electrolyte described in the first aspect, or is prepared by the injection method described in the third aspect.

[0073] In the above lithium-ion battery, as an optional embodiment, the lithium-ion battery further includes a positive electrode sheet, a negative electrode sheet and a separator, the positive electrode sheet includes a positive electrode collector and a positive electrode active membrane layer, wherein the positive electrode active membrane layer includes a lithium supplement.

[0074] In the above lithium-ion battery, as an optional implementation, the positive electrode current collector includes aluminum foil.

[0075] In the above lithium-ion battery, as an optional embodiment, the chemical formula of the lithium supplement is Li x M y O z , where M represents a transition metal, 1≤x≤6, 1≤y≤2, 2≤z≤4.

[0076] In the above lithium-ion battery, as an optional implementation, the M represents at least one of Co, Ni, Mo, Fe, and Cu.

[0077] In the above lithium-ion battery, as an optional implementation, the lithium supplement includes at least one of lithium nickel oxide, lithium ferrite, and lithium oxide, for example, including Li5FeO4.

[0078] In the above lithium-ion battery, as an optional embodiment, in the positive electrode active membrane layer, the content of the lithium supplement agent is 0.3wt%-10wt%, for example, it can be 0.3wt%, 1wt%, 2wt%, 4wt%, 6wt% or 10wt%.

[0079] In the above lithium-ion battery, as an optional implementation, the positive electrode active membrane layer further includes a positive electrode active material, a conductive agent and a binder.

[0080] In the above lithium-ion battery, as an optional implementation, in the positive electrode active film layer, the content of the positive electrode active material is 80wt%-97wt%, for example, 80wt%, 85wt%, 90wt% or 97wt%.

[0081] In the above lithium-ion battery, as an optional implementation, the positive electrode active material includes at least one of lithium iron phosphate, lithium nickel cobalt manganese oxide, lithium cobalt oxide, and lithium manganese iron phosphate.

[0082] In the above-mentioned lithium-ion battery, as an optional embodiment, in the positive electrode active membrane layer, the content of the conductive agent is 0.8wt%-10wt%, for example, it can be 0.8wt%, 1wt%, 2wt%, 4wt%, 6wt% or 10wt%; the content of the binder is 0.5wt%-10wt%, for example, it can be 0.5wt%, 1wt%, 2wt%, 4wt%, 6wt% or 10wt%.

[0083] In the above lithium-ion battery, as an optional embodiment, the negative electrode plate includes a negative electrode current collector and a negative electrode active film layer, wherein the negative electrode current collector includes copper foil, and the negative electrode active film layer includes a negative electrode active material, a conductive agent and a binder.

[0084] In the above lithium-ion battery, as an optional implementation, in the negative electrode active film layer, the content of the negative electrode active material is 80wt%-97wt%, for example, 80wt%, 85wt%, 90wt% or 97wt%.

[0085] In the above lithium-ion battery, as an optional implementation, the negative electrode active material includes at least one of graphite, silicon-based materials, and hard carbon materials.

[0086] The present invention will be further described in detail below with reference to specific embodiments and comparative examples.

[0087] Example 1

[0088] The present embodiment provides an electrolyte, the electrolyte comprising a first electrolyte for the first injection and a second electrolyte for the second injection, the mass ratio of the first electrolyte to the second electrolyte is 44:6, the first electrolyte comprises a first solvent, a first lithium salt and a first additive, the second electrolyte comprises a second solvent, a second lithium salt and a second additive, wherein, based on the total mass of the first electrolyte being 100%, the mass proportion of the first solvent in the first electrolyte is 81.2%, the first solvent is composed of DMC (dimethyl carbonate), EMC (ethyl methyl carbonate) and EC (ethylene carbonate), the mass ratio of DMC, EMC and EC is 3:4:3, the first lithium salt is composed of lithium hexafluorophosphate and lithium bisfluorosulfonyl imide, the mass proportion of the lithium hexafluorophosphate in the first electrolyte is 12.5%, the mass proportion of the lithium bisfluorosulfonyl imide in the first electrolyte is 3%, the first additive is VC (vinyl carbonate), FEC (fluoroethylene carbonate), DTD (vinyl sulfate) and DMS (dimethyl sulfide) ), the mass proportion of VC in the first electrolyte is 1.8%, the mass proportion of FEC in the first electrolyte is 0.5%, the mass proportion of DTD in the first electrolyte is 0.5%, and the mass proportion of DMS in the first electrolyte is 0.5%; taking the total mass of the second electrolyte as 100%, the mass proportion of the second solvent in the second electrolyte is 74.35%, and the second solvent is composed of DMC (dimethyl carbonate), EMC (ethyl methyl carbonate) and EC ( The second electrolyte comprises vinyl carbonate (VC) and triphenyl phosphite (TPPI), the mass ratio of which is 3:4:3; the second lithium salt comprises lithium hexafluorophosphate and lithium bisfluorosulfonyl imide, the mass ratio of which is 12.5% ​​in the second electrolyte, the mass ratio of which is 3% in the second electrolyte, and the second additive comprises VC (vinyl carbonate) and Tppi (triphenyl phosphite), the mass ratio of which is 10% in the second electrolyte, and the mass ratio of which is 0.15% in the second electrolyte.

[0089] The preparation method of the electrolyte comprises the following steps:

[0090] Weigh each component according to the designed ratio, mix the weighed DMC (dimethyl carbonate), EMC (ethyl methyl carbonate) and EC (ethylene carbonate), then add lithium hexafluorophosphate and lithium bis(fluorosulfonyl)imide, mix evenly, and obtain a first primary electrolyte; add VC (vinylene carbonate), FEC (fluoroethylene carbonate), DTD (vinyl sulfate) and DMS (dimethyl sulfide) to the first primary electrolyte, mix evenly, and obtain the first electrolyte;

[0091] Weigh each component according to the designed ratio, mix the weighed DMC (dimethyl carbonate), EMC (ethyl methyl carbonate), EC (ethylene carbonate), lithium hexafluorophosphate and lithium bis(fluorosulfonyl)imide evenly to obtain a second primary electrolyte; add VC (vinylene carbonate) and Tppi (triphenyl phosphite) to the second primary electrolyte, mix evenly to obtain the second electrolyte.

[0092] This embodiment also provides a lithium-ion battery, which includes a positive electrode sheet, a negative electrode sheet and a separator, wherein:

[0093] Positive electrode sheet: contains aluminum foil and active membrane layer, wherein the active membrane layer contains lithium iron phosphate, conductive agent (conductive carbon black (Super-P)), binder (polyvinylidene fluoride (PVDF)), lithium supplement agent, and the mass proportion of each component is 93:3:2:2 respectively; wherein the lithium supplement agent is Li5FeO4;

[0094] Negative electrode sheet: contains copper foil and active membrane layer, wherein the active membrane layer contains artificial graphite, conductive agent (Super-P), binder (CMC and SBR), and the mass proportion of each component is 95:2:1.8:1.2 respectively;

[0095] Separation membrane: A polyethylene porous polymer membrane is used as the separation membrane.

[0096] The preparation method of the lithium ion battery comprises the following steps:

[0097] The positive electrode sheet, the separator, and the negative electrode sheet are assembled according to the designed size and order, so that the separator can completely isolate the positive electrode from the negative electrode sheet, and at the same time, the negative electrode sheet can be completely covered with the positive electrode to form a roll core, which is placed in an outer package. After baking until the moisture content is qualified, 35.2g of the prepared first electrolyte is injected and packaged, and the battery is allowed to stand at 45°C for 24 hours for full infiltration, and then the formation and overcharge lithium replenishment processes are carried out. Then, 4.8g of the prepared second electrolyte is injected and packaged, and the battery is allowed to stand at 45°C for 24 hours for full infiltration again. After the electrolytes are mixed, the capacity division charging process is carried out, and the capacity is obtained after the end. A lithium-ion battery with a capacity of 10Ah, wherein the formation process includes: charging at a constant current of 0.1C for 7 minutes at 45°C, and then charging at a constant current of 0.2C for 120 minutes; the overcharge lithium replenishment process includes: charging at a constant current of 0.5C to 3.65V at 45°C, and then charging at a constant current of 0.2C to 4.3V; the capacity-differential charging process includes: discharging at a constant current of 0.5C to 2.5V at room temperature, and then charging at a constant current of 0.5C to 3.65V, standing for 10 minutes, discharging at a constant current of 0.5C to 2.5V, and finally charging at a constant current of 1C for 12 minutes.

[0098] Example 2

[0099] The electrolyte provided in this embodiment is substantially the same as that in embodiment 1, except that the mass proportion of the DMS in the first electrolyte is 1%, and the mass proportion of the first solvent in the first electrolyte is 80.7%. Specifically, the electrolyte comprises a first electrolyte for the first injection and a second electrolyte for the second injection, the mass ratio of the first electrolyte to the second electrolyte is 44:6, the first electrolyte comprises a first solvent, a first lithium salt and a first additive, the second electrolyte comprises a second solvent, a second lithium salt and a second additive, wherein the first electrolyte comprises a first solvent, a first lithium salt and a second additive. The total mass of an electrolyte is 100%, the mass proportion of the first solvent in the first electrolyte is 80.7%, the first solvent is composed of DMC (dimethyl carbonate), EMC (ethyl methyl carbonate) and EC (ethylene carbonate), and the mass ratio of DMC, EMC and EC is 3:4:3, the first lithium salt is composed of lithium hexafluorophosphate and lithium bisfluorosulfonyl imide, the mass proportion of the lithium hexafluorophosphate in the first electrolyte is 12.5%, the mass proportion of the lithium bisfluorosulfonyl imide in the first electrolyte is 3%, and the first additive is VC (vinyl carbonate) The first electrolyte is composed of VC (1.8%), FEC (0.5%), DTD (0.5%) and DMS (dimethyl sulfide), wherein the mass proportion of VC in the first electrolyte is 1.8%, the mass proportion of FEC in the first electrolyte is 0.5%, the mass proportion of DTD in the first electrolyte is 0.5%, and the mass proportion of DMS in the first electrolyte is 1%; taking the total mass of the second electrolyte as 100%, the mass proportion of the second solvent in the second electrolyte is 74.35%, and the second solvent is DMC (dimethyl carbonate). Ester), EMC (ethyl methyl carbonate) and EC (ethylene carbonate) are composed in a mass ratio of 3:4:3, the second lithium salt is composed of lithium hexafluorophosphate and lithium bisfluorosulfonyl imide, the mass proportion of the lithium hexafluorophosphate in the second electrolyte is 12.5%, the mass proportion of the lithium bisfluorosulfonyl imide in the second electrolyte is 3%, the second additive is composed of VC (vinylene carbonate) and Tppi (triphenyl phosphite), the mass proportion of the VC in the second electrolyte is 10%, and the mass proportion of the Tppi in the second electrolyte is 0.15%.

[0100] The electrolyte was prepared according to the preparation method of the electrolyte provided in Example 1.

[0101] A lithium ion battery with a capacity of 10 Ah was prepared by referring to the preparation method of the lithium ion battery provided in Example 1.

[0102] Example 3

[0103] The electrolyte provided in this embodiment is substantially the same as that in embodiment 1, except that the mass proportion of the DMS in the first electrolyte is 3%, the mass proportion of the first solvent in the first electrolyte is 78.7%, specifically, the electrolyte comprises a first electrolyte for the first injection and a second electrolyte for the second injection, the mass ratio of the first electrolyte to the second electrolyte is 44:6, the first electrolyte comprises a first solvent, a first lithium salt and a first additive, the second electrolyte comprises a second solvent, a second lithium salt and a second additive, wherein the first electrolyte comprises a first solvent, a first lithium salt and a second additive, The total mass of an electrolyte is 100%, the mass proportion of the first solvent in the first electrolyte is 78.7%, the first solvent is composed of DMC (dimethyl carbonate), EMC (ethyl methyl carbonate) and EC (ethylene carbonate), and the mass ratio of DMC, EMC and EC is 3:4:3, the first lithium salt is composed of lithium hexafluorophosphate and lithium bisfluorosulfonyl imide, the mass proportion of the lithium hexafluorophosphate in the first electrolyte is 12.5%, the mass proportion of the lithium bisfluorosulfonyl imide in the first electrolyte is 3%, and the first additive is VC (vinyl carbonate) The first electrolyte is composed of VC (1.8%), FEC (0.5%), DTD (0.5%) and DMS (dimethyl sulfide), wherein the mass proportion of VC in the first electrolyte is 1.8%, the mass proportion of FEC in the first electrolyte is 0.5%, the mass proportion of DTD in the first electrolyte is 0.5%, and the mass proportion of DMS in the first electrolyte is 3%; taking the total mass of the second electrolyte as 100%, the mass proportion of the second solvent in the second electrolyte is 74.35%, and the second solvent is DMC (dimethyl carbonate). Ester), EMC (ethyl methyl carbonate) and EC (ethylene carbonate) are composed in a mass ratio of 3:4:3, the second lithium salt is composed of lithium hexafluorophosphate and lithium bisfluorosulfonyl imide, the mass proportion of the lithium hexafluorophosphate in the second electrolyte is 12.5%, the mass proportion of the lithium bisfluorosulfonyl imide in the second electrolyte is 3%, the second additive is composed of VC (vinylene carbonate) and Tppi (triphenyl phosphite), the mass proportion of the VC in the second electrolyte is 10%, and the mass proportion of the Tppi in the second electrolyte is 0.15%.

[0104] The electrolyte was prepared according to the preparation method of the electrolyte provided in Example 1.

[0105] A lithium ion battery with a capacity of 10 Ah was prepared by referring to the preparation method of the lithium ion battery provided in Example 1.

[0106] Example 4

[0107] The electrolyte provided in this embodiment is substantially the same as that in embodiment 2, except that the mass proportion of Tppi in the second electrolyte is 0.03%, and the mass proportion of the second solvent in the second electrolyte is 74.47%. Specifically, the electrolyte includes a first electrolyte for the first injection and a second electrolyte for the second injection, and the mass ratio of the first electrolyte to the second electrolyte is 44:6. The first electrolyte includes a first solvent, a first lithium salt and a first additive, and the second electrolyte includes a second solvent, a second lithium salt and a second additive, wherein, Taking the total mass of the first electrolyte as 100%, the mass proportion of the first solvent in the first electrolyte is 80.7%, the first solvent is composed of DMC (dimethyl carbonate), EMC (ethyl methyl carbonate) and EC (ethylene carbonate), and the mass ratio of DMC, EMC and EC is 3:4:3, the first lithium salt is composed of lithium hexafluorophosphate and lithium bisfluorosulfonyl imide, the mass proportion of the lithium hexafluorophosphate in the first electrolyte is 12.5%, the mass proportion of the lithium bisfluorosulfonyl imide in the first electrolyte is 3%, and the first additive is VC (ethylene carbonate) The first electrolyte is composed of VC (ethylene ester), FEC (fluoroethylene carbonate), DTD (ethylene sulfate) and DMS (dimethyl sulfide), wherein the mass proportion of VC in the first electrolyte is 1.8%, the mass proportion of FEC in the first electrolyte is 0.5%, the mass proportion of DTD in the first electrolyte is 0.5%, and the mass proportion of DMS in the first electrolyte is 1%; taking the total mass of the second electrolyte as 100%, the mass proportion of the second solvent in the second electrolyte is 74.47%, and the second solvent is DMC (dimethyl carbonate). The second electrolyte comprises: methyl ester), EMC (ethyl methyl carbonate) and EC (ethylene carbonate) in a mass ratio of 3:4:3, the second lithium salt comprises lithium hexafluorophosphate and lithium bisfluorosulfonyl imide, the mass proportion of the lithium hexafluorophosphate in the second electrolyte is 12.5%, the mass proportion of the lithium bisfluorosulfonyl imide in the second electrolyte is 3%, the second additive comprises VC (vinylene carbonate) and Tppi (triphenyl phosphite), the mass proportion of the VC in the second electrolyte is 10%, and the mass proportion of the Tppi in the second electrolyte is 0.03%.

[0108] The electrolyte was prepared according to the preparation method of the electrolyte provided in Example 1.

[0109] A lithium ion battery with a capacity of 10 Ah was prepared by referring to the preparation method of the lithium ion battery provided in Example 1.

[0110] Example 5

[0111] The electrolyte provided in this embodiment is substantially the same as that in embodiment 2, except that the mass proportion of Tppi in the second electrolyte is 0.5%, and the mass proportion of the second solvent in the second electrolyte is 74%. Specifically, the electrolyte comprises a first electrolyte for the first injection and a second electrolyte for the second injection, and the mass ratio of the first electrolyte to the second electrolyte is 44:6. The first electrolyte comprises a first solvent, a first lithium salt and a first additive, and the second electrolyte comprises a second solvent, a second lithium salt and a second additive, wherein the mass ratio of the first electrolyte to the second electrolyte is 44:6. The total mass of the first electrolyte is 100%, the mass proportion of the first solvent in the first electrolyte is 80.7%, the first solvent is composed of DMC (dimethyl carbonate), EMC (ethyl methyl carbonate) and EC (ethylene carbonate), and the mass ratio of DMC, EMC and EC is 3:4:3, the first lithium salt is composed of lithium hexafluorophosphate and lithium bisfluorosulfonyl imide, the mass proportion of the lithium hexafluorophosphate in the first electrolyte is 12.5%, the mass proportion of the lithium bisfluorosulfonyl imide in the first electrolyte is 3%, and the first additive is VC (ethylene carbonate) The first electrolyte is composed of 1.8% by weight of VC, 0.5% by weight of FEC, 0.5% by weight of DTD, and 1% by weight of DMS; based on the total weight of the second electrolyte being 100%, the second solvent in the second electrolyte is 74% by weight, and the second solvent is composed of DMC (dimethyl carbonate). Ester), EMC (ethyl methyl carbonate) and EC (ethylene carbonate) are composed in a mass ratio of 3:4:3, the second lithium salt is composed of lithium hexafluorophosphate and lithium bisfluorosulfonyl imide, the mass proportion of the lithium hexafluorophosphate in the second electrolyte is 12.5%, the mass proportion of the lithium bisfluorosulfonyl imide in the second electrolyte is 3%, the second additive is composed of VC (vinylene carbonate) and Tppi (triphenyl phosphite), the mass proportion of the VC in the second electrolyte is 10%, and the mass proportion of the Tppi in the second electrolyte is 0.5%.

[0112] The electrolyte was prepared according to the preparation method of the electrolyte provided in Example 1.

[0113] A lithium ion battery with a capacity of 10 Ah was prepared by referring to the preparation method of the lithium ion battery provided in Example 1.

[0114] Example 6

[0115] The electrolyte provided in this embodiment is substantially the same as that in embodiment 2, except that the mass ratio of VC in the first additive in the first electrolyte is 2.2%, the mass ratio of the first solvent in the first electrolyte is 80.3%, the mass ratio of VC in the second additive in the second electrolyte is 7%, and the mass ratio of the second solvent in the second electrolyte is 77.35%. Specifically, the electrolyte comprises a first electrolyte for the first injection and a second electrolyte for the second injection, the mass ratio of the first electrolyte to the second electrolyte is 44:6, and the first electrolyte comprises The first electrolyte comprises a first solvent, a first lithium salt and a first additive, the second electrolyte comprises a second solvent, a second lithium salt and a second additive, wherein, based on the total mass of the first electrolyte being 100%, the mass proportion of the first solvent in the first electrolyte is 80.3%, the first solvent is composed of DMC (dimethyl carbonate), EMC (ethyl methyl carbonate) and EC (ethylene carbonate), the mass ratio of DMC, EMC and EC is 3:4:3, the first lithium salt is composed of lithium hexafluorophosphate and lithium bisfluorosulfonyl imide, the mass proportion of the lithium hexafluorophosphate in the first electrolyte is 12.5%, the mass ratio of the lithium bisfluorosulfonyl imide is The mass proportion of the first electrolyte is 3%, and the first additive is composed of VC (vinyl carbonate), FEC (fluoroethylene carbonate), DTD (vinyl sulfate) and DMS (dimethyl sulfide), the mass proportion of VC in the first electrolyte is 2.2%, the mass proportion of FEC in the first electrolyte is 0.5%, the mass proportion of DTD in the first electrolyte is 0.5%, and the mass proportion of DMS in the first electrolyte is 1%; based on the total mass of the second electrolyte being 100%, the mass proportion of the second solvent in the second electrolyte is 77.35 The second solvent is composed of DMC (dimethyl carbonate), EMC (ethyl methyl carbonate) and EC (ethylene carbonate) in a mass ratio of 3:4:3, the second lithium salt is composed of lithium hexafluorophosphate and lithium bisfluorosulfonyl imide, the mass proportion of the lithium hexafluorophosphate in the second electrolyte is 12.5%, the mass proportion of the lithium bisfluorosulfonyl imide in the second electrolyte is 3%, the second additive is composed of VC (vinylene carbonate) and Tppi (triphenyl phosphite), the mass proportion of the VC in the second electrolyte is 7%, and the mass proportion of the Tppi in the second electrolyte is 0.15%.

[0116] The electrolyte was prepared according to the preparation method of the electrolyte provided in Example 1.

[0117] A lithium ion battery with a capacity of 10 Ah was prepared by referring to the preparation method of the lithium ion battery provided in Example 1.

[0118] Example 7

[0119] The electrolyte provided in this embodiment is substantially the same as that in Embodiment 1, except that the mass proportion of the VC in the second electrolyte is 20%, and the mass proportion of the second solvent in the second electrolyte is 64.35%.

[0120] The electrolyte was prepared according to the preparation method of the electrolyte provided in Example 1.

[0121] A lithium ion battery with a capacity of 10 Ah was prepared by referring to the preparation method of the lithium ion battery provided in Example 1.

[0122] Comparative Example 1

[0123] This comparative example provides an electrolyte, which includes a solvent, a lithium salt and an additive, wherein, based on the total mass of the electrolyte being 100%, the mass proportion of the solvent in the electrolyte is 80.72%, the solvent is composed of DMC (dimethyl carbonate), EMC (ethyl methyl carbonate) and EC (ethylene carbonate), and the mass ratio of DMC, EMC and EC is 3:4:3, the lithium salt is composed of lithium hexafluorophosphate and lithium bisfluorosulfonyl imide, the mass proportion of the lithium hexafluorophosphate in the electrolyte is 12.5%, the mass proportion of the lithium bisfluorosulfonyl imide in the electrolyte is 3%, the additive is composed of VC (vinylene carbonate), FEC (fluoroethylene carbonate) and DTD (vinyl sulfate), the mass proportion of VC in the electrolyte is 2.78%, the mass proportion of FEC in the electrolyte is 0.5%, and the mass proportion of DTD in the electrolyte is 0.5%.

[0124] The electrolyte was prepared according to the preparation method of the electrolyte provided in Example 1.

[0125] This comparative example also provides a lithium-ion battery, which includes a positive electrode sheet, a negative electrode sheet and a separator, wherein:

[0126] Positive electrode sheet: contains aluminum foil and active membrane layer, wherein the active membrane layer contains lithium iron phosphate, conductive agent (conductive carbon black (Super-P)), binder (polyvinylidene fluoride (PVDF)), lithium supplement agent, and the mass proportion of each component is 93:3:2:2 respectively; wherein the lithium supplement agent is Li5FeO4;

[0127] Negative electrode sheet: contains copper foil and active membrane layer, wherein the active membrane layer contains artificial graphite, conductive agent (Super-P), binder (CMC and SBR), and the mass proportion of each component is 95:2:1.8:1.2 respectively;

[0128] Separation membrane: A polyethylene porous polymer membrane is used as the separation membrane.

[0129] The preparation method of the lithium ion battery comprises the following steps:

[0130] The positive electrode sheet, separator, and negative electrode sheet are assembled according to the designed size and order, so that the separator can completely isolate the positive electrode from the negative electrode sheet, and the negative electrode sheet can be completely covered to form a winding core, which is placed in an outer package, baked until the moisture content is qualified, and then 40g of the prepared electrolyte is injected and packaged, and allowed to stand at 45°C for 24 hours to fully infiltrate, and then the formation, overcharge and lithium supplement, and divided capacity charging processes are carried out. After the completion of the process, a lithium-ion battery with a capacity of 10Ah is obtained by packaging, wherein the formation process includes: at 45 ℃, charging at 0.1C constant current for 7 minutes, and then charging at 0.2C constant current for 120 minutes; the overcharge lithium replenishment process includes: at 45℃, first charging to 3.65V at 0.5C constant current, and then charging to 4.3V at 0.2C constant current; the differentiated capacity charging process includes: under normal temperature conditions, discharging to 2.5V at 0.5C constant current, and then charging to 3.65V at 0.5C constant current, standing for 10 minutes, discharging to 2.5V at 0.5C constant current, and finally charging at 1C constant current for 12 minutes.

[0131] Comparative Example 2

[0132] The electrolyte provided in this comparative example is basically the same as that in Example 1, except that the second additive does not include Tppi. Specifically, the electrolyte includes a first electrolyte for the first injection and a second electrolyte for the second injection, the mass ratio of the first electrolyte to the second electrolyte is 44:6, the first electrolyte includes a first solvent, a first lithium salt and a first additive, and the second electrolyte includes a second solvent, a second lithium salt and a second additive, wherein, based on the total mass of the first electrolyte being 100%, the mass proportion of the first solvent in the first electrolyte is 81.2%, the first solvent is composed of DMC (dimethyl carbonate), EMC (ethyl methyl carbonate) and EC (ethylene carbonate), the mass ratio of DMC, EMC and EC is 3:4:3, the first lithium salt is composed of lithium hexafluorophosphate and lithium bis(fluorosulfonyl)imide, the mass proportion of the lithium hexafluorophosphate in the first electrolyte is 12.5%, the mass proportion of the lithium bis(fluorosulfonyl)imide in the first electrolyte is 3%, and the first additive is VC (carbonate) The invention relates to a first electrolyte comprising: a first electrolyte comprising: a first solvent and a second solvent. The first electrolyte comprises: a first electrolyte comprising: a first solvent and a second solvent. The first electrolyte comprises: a first electrolyte comprising: a first solvent and a second solvent. The first electrolyte comprises: a first electrolyte comprising: a first solvent and a second solvent. The first electrolyte comprises: a first electrolyte comprising: a first electrolyte comprising: a first electrolyte comprising: a first electrolyte comprising: a first electrolyte comprising: a first electrolyte comprising: a first electrolyte comprising: a first electrolyte comprising: a first electrolyte comprising: a first electrolyte comprising: a first electrolyte comprising: a first electrolyte comprising: a first electrolyte comprising: a first electrolyte comprising: a first electrolyte comprising: a first electrolyte comprising: a first electrolyte comprising: a first electrolyte comprising: a first electrolyte comprising: a first electrolyte comprising: a first electrolyte comprising: a first electrolyte comprising: a second ...

[0133] The electrolyte was prepared according to the preparation method of the electrolyte provided in Example 1.

[0134] A lithium ion battery with a capacity of 10 Ah was prepared by referring to the preparation method of the lithium ion battery provided in Example 1.

[0135] Comparative Example 3

[0136] The electrolyte provided in this comparative example is basically the same as that in Example 1, except that the first additive does not include DMS (dimethyl sulfide). Specifically, the electrolyte includes a first electrolyte for the first injection and a second electrolyte for the second injection, the mass ratio of the first electrolyte to the second electrolyte is 44:6, the first electrolyte includes a first solvent, a first lithium salt and a first additive, and the second electrolyte includes a second solvent, a second lithium salt and a second additive, wherein, based on the total mass of the first electrolyte as 100%, the mass proportion of the first solvent in the first electrolyte is 81.7%, the first solvent is composed of DMC (dimethyl carbonate), EMC (ethyl methyl carbonate) and EC (ethylene carbonate), the mass ratio of DMC, EMC and EC is 3:4:3, the first lithium salt is composed of lithium hexafluorophosphate and lithium bis(fluorosulfonyl)imide, the mass proportion of the lithium hexafluorophosphate in the first electrolyte is 12.5%, the mass proportion of the lithium bis(fluorosulfonyl)imide in the first electrolyte is 3%, and the first additive is VC (ethylene carbonate) The first electrolyte comprises 1.8% by weight of VC, 0.5% by weight of FEC, and 0.5% by weight of DTD. Taking the total weight of the second electrolyte as 100%, the weight of the second solvent in the second electrolyte is 74.35%. The second solvent comprises DMC (dimethyl carbonate), EMC (ethyl methyl carbonate) and EC. (ethylene carbonate) is composed of a mass ratio of 3:4:3, the second lithium salt is composed of lithium hexafluorophosphate and lithium bisfluorosulfonyl imide, the mass proportion of the lithium hexafluorophosphate in the second electrolyte is 12.5%, the mass proportion of the lithium bisfluorosulfonyl imide in the second electrolyte is 3%, the second additive is composed of VC (vinyl carbonate) and Tppi (triphenyl phosphite), the mass proportion of the VC in the second electrolyte is 10%, and the mass proportion of the Tppi in the second electrolyte is 0.15%.

[0137] The electrolyte was prepared according to the preparation method of the electrolyte provided in Example 1.

[0138] A lithium ion battery with a capacity of 10 Ah was prepared by referring to the preparation method of the lithium ion battery provided in Example 1.

[0139] Comparative Example 4

[0140] The electrolyte provided in this comparative example is substantially the same as that in Example 1, except that DMS in the first additive is replaced by DTD (vinyl sulfate), that is, the first additive does not include DMS, and the mass proportion of DTD in the first electrolyte is 1%.

[0141] The electrolyte was prepared according to the preparation method of the electrolyte provided in Example 1.

[0142] A lithium ion battery with a capacity of 10 Ah was prepared by referring to the preparation method of the lithium ion battery provided in Example 1.

[0143] Comparative Example 5

[0144] The electrolyte provided in this comparative example is substantially the same as that in Example 1, except that DMS in the first additive is replaced by allyl phenyl sulfide (CAS No.: 5296-64-0).

[0145] The electrolyte was prepared according to the preparation method of the electrolyte provided in Example 1.

[0146] A lithium ion battery with a capacity of 10 Ah was prepared by referring to the preparation method of the lithium ion battery provided in Example 1.

[0147] Comparative Example 6

[0148] The electrolyte provided in this comparative example is basically the same as that in Example 1, except that DMS (dimethyl sulfide) in the first additive is replaced by Tppi (triphenyl phosphite), and the mass proportion of Tppi in the first electrolyte is 0.5%, and Tppi (triphenyl phosphite) in the second additive is replaced by DMS (dimethyl sulfide), and the mass proportion of DMS (dimethyl sulfide) in the second electrolyte is 0.15%.

[0149] The electrolyte was prepared according to the preparation method of the electrolyte provided in Example 1.

[0150] A lithium ion battery with a capacity of 10 Ah was prepared by referring to the preparation method of the lithium ion battery provided in Example 1.

[0151] Comparative Example 7

[0152] The electrolyte provided in this comparative example is basically the same as that in Example 1, except that the mass proportion of VC in the first additive in the first electrolyte is 2.92%, the mass proportion of the first solvent in the first electrolyte is 80.08%, the mass proportion of VC in the second additive in the second electrolyte is 1.8%, and the mass proportion of the second solvent in the second electrolyte is 82.55%.

[0153] The electrolyte was prepared according to the preparation method of the electrolyte provided in Example 1.

[0154] A lithium ion battery with a capacity of 10 Ah was prepared by referring to the preparation method of the lithium ion battery provided in Example 1.

[0155] Performance Testing

[0156] The performance of the lithium-ion batteries provided in the embodiments and comparative examples was tested, and the specific testing process is as follows:

[0157] Full charge: The lithium-ion batteries provided in the embodiments and comparative examples are first charged at 1C constant current to 3.65V at 25°C, and then charged at a constant voltage until the current reaches 0.05C, to obtain fully charged batteries.

[0158] Capacity-divided full charge (charged to 100% SOC) electrode interface condition detection: The fully charged battery was disassembled under the condition of humidity <10%, and the interface of the battery negative electrode was observed with the naked eye. The results are shown in Table 1.

[0159] High-temperature gas production: The fully charged battery is placed in water at a temperature of 60°C for a water displacement test of volume V1; after the temperature is raised to 60°C in a constant temperature box, it is stored for 5 days, and then the battery is taken out and placed in water at a temperature of 60°C for a water displacement test of volume V2 again. The volume change is V2-V1. The volume change value is recorded in Table 1. The high-temperature gas production is judged by the volume change. The greater the volume change, the more gas is produced.

[0160] Storage performance: Before high-temperature storage, the fully charged battery was discharged at 1C constant current to 2.5V to obtain the initial discharge capacity C1; the battery continued to be fully charged, and after the temperature was raised to 55°C in the constant temperature box, it was stored for 7 days. After the battery was discharged, it was fully charged again, and then discharged at 1C constant current to 2.5V again to obtain the current capacity C2. The capacity recovery rate is C2 / C1*100%. The results are shown in Table 1.

[0161] Table 1

[0162]

[0163] From Table 1, we can see at least the following points:

[0164] (1) By comparing Example 1 with Comparative Example 1, it can be seen that although vinyl sulfate is added to the existing electrolyte to improve the effect of oxygen released during lithium replenishment on battery performance, the damage caused by oxygen free radicals released during the decomposition of the lithium-rich material is still serious, gas production is relatively large, and black spots appear on the negative electrode interface. The present invention improves the problems of high-temperature gas production and black spots on the negative electrode interface during the use of the lithium-rich material lithium replenisher by including dimethyl sulfide (DMS) in the first additive and triphenyl phosphite (Tppi) in the second additive, thereby improving the calendar storage life of the lithium-ion battery.

[0165] (2) By comparing Example 2 with Example 6, it can be seen that when the total VC content in the electrolyte remains unchanged, when the mass proportion of VC in the first electrolyte exceeds 2% and the mass proportion of VC in the second electrolyte is less than 10%, the calendar storage life of the lithium-ion battery is reduced. The applicant analyzed that the reason may be that VC has weak oxidation resistance and is easy to participate in the reaction and decomposition under high voltage and high oxidizing environment, which can easily lead to more gas production, resulting in black spots on the battery negative electrode interface and even lithium precipitation. After formation and before the decomposition of the lithium supplement material, reducing the free VC in the electrolyte can reduce its negative effect after oxidation, increase the content of vinylene carbonate (VC) in the second electrolyte, and ensure that there is a sufficient amount of film-forming additive for the repair of SEI during the later cycle and storage process. Similarly, by comparing Example 1 with Comparative Example 7, it can be seen that when the mass proportion of VC in the first electrolyte further increases and the mass proportion of VC in the second electrolyte further decreases, the mass proportion of VC in the first electrolyte is greater than the mass proportion in the second electrolyte, black spots appear on the negative electrode interface, more gas is produced, and the calendar storage life is further reduced.

[0166] (3) By comparing Example 1 with Comparative Example 4, it can be seen that after DMS is replaced with conventional DTD (vinyl sulfate), black spots appear on the negative electrode interface, more gas is produced, and the calendar storage life is significantly reduced.

[0167] (4) By comparing Example 1 with Comparative Example 5, it can be seen that after DMS is replaced with other sulfide compounds, lithium precipitation occurs in the negative electrode plate, more gas is produced, and the calendar storage life is significantly reduced.

[0168] (5) By comparing Example 1 with Comparative Example 6, it can be seen that when DMS (dimethyl sulfide) and Tppi (triphenyl phosphite) are sequentially exchanged in the electrolyte, that is, Tppi (triphenyl phosphite) is added to the first electrolyte used for the first injection, and DMS (dimethyl sulfide) is added to the second electrolyte used for the second injection, black spots appear on the negative electrode interface, more gas is produced, and the calendar storage life is reduced.

[0169] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. An electrolyte, characterized in that: The electrolyte includes a first electrolyte for the first injection and a second electrolyte for the second injection, the first electrolyte includes a first solvent, a first lithium salt and a first additive, the second electrolyte includes a second solvent, a second lithium salt and a second additive, wherein the mass percentage of the second electrolyte to the electrolyte is 5% to 20%, the first additive includes dimethyl sulfide and vinylene carbonate, and the second additive includes triphenyl phosphite and vinylene carbonate.

2. The electrolyte according to claim 1, characterized in that The first solvent comprises at least two of dimethyl carbonate, ethyl methyl carbonate, ethylene carbonate, propylene carbonate, diethyl carbonate, ethyl formate, and ethyl propionate; and / or, in the first solvent, the weight ratio between every two compounds is (2-5):(2-5); And / or, the first lithium salt includes at least one of lithium hexafluorophosphate and lithium bis(fluorosulfonyl)imide; And / or, based on the total mass of the first electrolyte being 100%, the mass proportion of the first solvent in the first electrolyte is 75-90%, the mass proportion of the first lithium salt in the first electrolyte is 7%-20%, and the mass proportion of the first additive in the first electrolyte is 0.3%-7%.

3. The electrolyte according to claim 1, characterized in that The first additive further comprises at least one of methylene disulfonate, lithium difluorophosphate, fluoroethylene carbonate, vinyl sulfate, 1,3-propane sultone, tris(trimethylsilane)phosphate, lithium difluorooxalatoborate, and difluorooxalatophosphate; And / or, the mass percentage of dimethyl sulfide in the first electrolyte is 0.1-3wt%; And / or, the mass percentage of vinylene carbonate in the first additive to the first electrolyte is not higher than 2%.

4. The electrolyte according to claim 1, characterized in that The second solvent comprises at least two of dimethyl carbonate, ethyl methyl carbonate, ethylene carbonate, propylene carbonate, diethyl carbonate, ethyl formate, and ethyl propionate; and / or, in the second solvent, the weight ratio between each two compounds is (2-5):(2-5); and / or, the second lithium salt comprises at least one of lithium hexafluorophosphate and lithium bis(fluorosulfonyl)imide; And / or, based on the total mass of the second electrolyte as 100%, the mass proportion of the second solvent in the second electrolyte is 52% to 82%, the mass proportion of the second lithium salt in the second electrolyte is 7% to 18%, and the mass proportion of the second additive in the second electrolyte is 10.01% to 30.5%.

5. The electrolyte according to claim 1, characterized in that The mass percentage of vinylene carbonate in the second additive in the second electrolyte is greater than the mass percentage of vinylene carbonate in the first additive in the first electrolyte; And / or, the mass percentage of triphenyl phosphite in the second electrolyte is 0.01-0.5%; And / or, the mass percentage of vinylene carbonate in the second additive to the second electrolyte is 10% to 30%.

6. A method for preparing an electrolyte according to any one of claims 1 to 5, characterized in that: The preparation method comprises the following steps: Weighing each component according to the designed ratio, and mixing the weighed first solvent and the first lithium salt uniformly to obtain a first primary electrolyte; adding the first additive to the first primary electrolyte, and mixing uniformly to obtain the first electrolyte; Weigh each component according to the designed ratio, mix the weighed second solvent and the second lithium salt evenly to obtain a second primary electrolyte; add the second additive to the second primary electrolyte, mix evenly, and obtain the second electrolyte.

7. A method for injecting an electrolyte according to any one of claims 1 to 5, characterized in that: The liquid injection method comprises the following steps: The first electrolyte is injected into the battery to be filled and sealed. After sufficient infiltration, the formation and overcharge lithium replenishment processes are carried out. Then the second electrolyte is injected and sealed. After sufficient infiltration again, the electrolytes are mixed and the capacity-divided charging process is carried out.

8. The electrolyte injection method according to claim 7, characterized in that: The sufficient infiltration includes standing at 20-60° C. for 12-36 hours.

9. A lithium ion battery, characterized in that: The lithium-ion battery comprises the electrolyte described in any one of claims 1 to 5, or is prepared by the injection method described in claim 7 or 8.

10. The lithium ion battery according to claim 9, characterized in that: The lithium-ion battery further comprises a positive electrode sheet, a negative electrode sheet and a separator, wherein the positive electrode sheet comprises a positive current collector and a positive active film layer, wherein the positive active film layer comprises a lithium replenisher, and the general chemical formula of the lithium replenisher is Li x M y O z , where M represents a transition metal, 1≤x≤6, 1≤y≤2, 2≤z≤4; And / or, the lithium supplement includes at least one of lithium nickel oxide, lithium ferrite, and lithium oxide.

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