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

Abstract

The present invention relates to the field of lithium-ion battery technology, and more particularly to an electrolyte, a preparation method thereof, an injection method, and a lithium-ion battery. The electrolyte comprises a first electrolyte for a first injection and a second electrolyte for a second injection. 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. The second electrolyte accounts for 5% to 20% of the electrolyte by mass, the first additive comprises dimethyl sulfide and vinylene carbonate, and the second additive comprises triphenyl phosphite and vinylene carbonate. By including dimethyl sulfide in the first additive and triphenyl phosphite in the second additive, the electrolyte improves the problems of high-temperature gassing and black spots at the negative electrode interface during use of lithium-rich material lithium supplements.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium ion batteries, and in particular to an electrolyte, 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, its energy density is relatively low due to its low specific capacity and the reaction loss of lithium during the first charging process. In addition, the cycle trend is often that the capacity loss is fast at first and then slow, which does not meet the market's requirement for slow decay in the early stage of the cycle. Positive electrode lithium replenishment technology is used in secondary batteries. Currently, positive electrode lithium replenishment in lithium iron phosphate systems mostly uses electrochemical methods. Lithium-rich materials are added to the positive electrode material. During the charging process, the lithium-rich materials complete the delithiation 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) is added to the positive electrode. During the battery formation stage, the charging voltage must be set to a higher voltage of 3.7V or above under high temperature conditions to complete the release of lithium ions and a certain amount of oxygen. At this time, the battery capacity and energy density are significantly improved. To improve the impact of oxygen released during lithium replenishment on battery performance, electrolyte additives containing sulfite and sulfonate are often used to form a protective film on the positive electrode, and to form a cross-linked negative electrode SEI to reduce damage from side reactions.

[0004] Existing electrolytes protect the negative electrode and the interface where the positive electrode reacts with the electrolyte. However, under high temperature and high voltage, the damage caused by oxygen free radicals released when lithium-rich materials decompose is still serious: oxidizing organic solvents to produce H2O, HF and other substances that are harmful to battery performance, resulting in more subsequent high-temperature side reactions in the battery, resulting in gas production and black spots on the negative electrode interface, thereby affecting the storage life and cycle life of the battery.

[0005] Therefore, how to provide an electrolyte that can improve the adverse problems of high-temperature gas production 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, a preparation method thereof, an injection method and a lithium-ion battery. The electrolyte improves the undesirable 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 in 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) as the first additive and triphenyl phosphite (Tppi) as the second additive, thereby improving the undesirable problems of high-temperature gas production and black spots on the negative electrode interface during the use of lithium-rich material lithium supplements.

[0010] Furthermore, 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 each two compounds is (2-5):(2-5);

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

[0013] And / or, 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%, 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] Furthermore, the first additive further comprises at least one of methylene methanedisulfonate, 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 to 3 wt%;

[0016] And / or, the mass percentage of vinylene carbonate in the first additive to the first electrolyte is no more than 2%.

[0017] Furthermore, 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] Furthermore, 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 uniformly mixing the weighed first solvent and the first lithium salt 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 the 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 the battery is sealed. After the battery is fully soaked, the formation and overcharge lithium replenishment processes are carried out. Then the second electrolyte is injected and the battery is sealed. The battery is fully soaked again, and the electrolytes are mixed before the capacity-divided charging process is carried out.

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

[0030] In a fourth aspect, the present invention provides a lithium-ion battery, which includes the electrolyte described in the first aspect, or is prepared using 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 electrode current collector and a positive electrode active membrane layer, wherein the positive electrode active membrane layer comprises a lithium supplement agent, and the general chemical formula of the lithium supplement agent 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 nickelate, lithium ferrite, and lithium oxide.

[0033] Compared with the prior art, the present invention has at least one of the following advantages:

[0034] (1) The electrolyte provided by the present invention 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.

[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 on the positive and negative electrodes, and at the same time uses a smaller amount of VC to participate in the film formation, so that the residual amount of VC after formation is smaller, and the oxidation of VC at high voltage is reduced; Tppi is added to the second electrolyte to annihilate the oxidizing components produced by some undecomposed lithium supplement additives, and capture the oxygen decomposed and escaped during the formation process and remaining in the battery, and convert 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 sufficient film-forming additive for the repair of SEI during the later cycle and storage process; thus, the combination can effectively improve the high-temperature gas production problem of the lithium supplement system and ensure the cycle stability of the battery after lithium supplementation. DETAILED DESCRIPTION

[0036] In order to make the purpose, technical solutions and advantages of the present invention clearer, the technical solutions in the embodiments 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 merely 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 those of ordinary skill in the art without making creative work are within the scope of protection of the present invention. The process parameters for which specific conditions are not specified in the following examples are generally in accordance with conventional conditions.

[0037] The endpoints of the ranges and any values ​​disclosed herein 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 endpoints of each range, the endpoints of each range and individual point values, and the individual point values ​​can be combined with each other to form one or more new numerical ranges, and these numerical ranges should be considered to be 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 in 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 the oxygen free radicals produced by the decomposition of the lithium supplement agent and generate a structurally stable positive electrode S-containing solid electrolyte membrane, which inactivates the 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, and capture the oxygen that escapes during the formation process and remains in the battery, and convert itself into a more pressure-resistant phosphate ester. This 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 use of lithium replenishment systems, improving the adverse problems of high-temperature gas production, interface black spots, and electrode peeling during the use of current lithium replenishers, thereby improving the cycle life and calendar storage life of the battery.

[0043] The electrolyte provided by the present invention includes dimethyl sulfide as the first additive and triphenyl phosphite as the second additive, thereby improving the undesirable problems of high-temperature gas production, black spots on the negative electrode interface, and electrode film peeling (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 embodiment, 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 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 embodiment, 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 electrolyte, as an optional embodiment, the first additive also includes at least one of methylene methanedisulfonate MMDS, lithium difluorophosphate LiPO2F2, fluoroethylene carbonate FEC, vinyl sulfate DTD, 1,3-propane sultone PS, tris(trimethylsilyl)phosphate TMSP, lithium difluorooxalatoborate LiDFOB, and difluorooxalatophosphate LiDFOP.

[0052] In the above electrolyte, as an optional embodiment, the first additive further 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 3 wt%, for example, it can be 0.1 wt%, 0.5 wt%, 1 wt%, 1.5 wt%, 2 wt%, 2.5 wt% or 3 wt%; when the content is too high, it will cause the system impedance to be too large, affecting the kinetic performance. 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 highly oxidizing environment, resulting in more gas production, causing black spots on the battery negative electrode interface 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 1% to 2% content has better performance.

[0055] In the above 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 each 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 embodiment, 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 embodiment, 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 sufficient film-forming additive for repairing SEI during later cycles and storage.

[0063] In the above-mentioned electrolyte, as an optional embodiment, 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 efficiency 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, 10%, 15%, 20% or 30%. If the content of vinylene carbonate (VC) in the second electrolyte is too low, the cycle life and storage performance are poor; if the content of vinylene carbonate (VC) in the second electrolyte is too high, the impedance is high, which may lead to lithium deposition 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 uniformly mixing the weighed first solvent and the first lithium salt 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 the battery is sealed. After the battery is fully soaked, the formation and overcharge lithium replenishment processes are carried out. Then the second electrolyte is injected and the battery is sealed. The battery is fully soaked again, and the electrolytes are mixed before 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 embodiment, 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 4.2-4.3V; the divided capacity charging process includes discharging at a constant current of 0.5C to 2.5V at room temperature, and then charging to 3.65V at a constant current of 0.5C, standing for 10 minutes, and then discharging to 2.5V at a constant current of 0.5C, and charging at a constant current of 1C for 12 minutes.

[0072] In a fourth aspect, the present invention provides a lithium-ion battery, which includes the electrolyte described in the first aspect, or is prepared using 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 current 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 embodiment, 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 embodiment, the M represents at least one of Co, Ni, Mo, Fe, and Cu.

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

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

[0079] In the above lithium-ion battery, as an optional embodiment, 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 embodiment, the content of the positive electrode active material in the positive electrode active membrane layer is 80wt%-97wt%, for example, 80wt%, 85wt%, 90wt% or 97wt%.

[0081] In the above lithium-ion battery, as an optional embodiment, 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 membrane layer, wherein the negative electrode current collector includes copper foil, and the negative electrode active membrane layer includes a negative electrode active material, a conductive agent and a binder.

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

[0085] In the above lithium-ion battery, as an optional embodiment, 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 examples and comparative examples.

[0087] Example 1

[0088] This embodiment provides an electrolyte, the electrolyte including 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), 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 (vinylene carbonate), FEC (fluoroethylene carbonate), DTD (ethylene sulfate) and DMS (dimethyl sulfide). ), the mass proportion of the VC in the first electrolyte is 1.8%, the mass proportion of the FEC in the first electrolyte is 0.5%, the mass proportion of the DTD in the first electrolyte is 0.5%, and the mass proportion of the DMS in the first electrolyte is 0.5%; based on the total mass of the second electrolyte being 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 a first electrolyte and a second electrolyte solution containing ethylene carbonate (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 0.15%.

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

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

[0091] The components are weighed according to the designed ratio, and the weighed DMC (dimethyl carbonate), EMC (ethyl methyl carbonate), EC (ethylene carbonate), lithium hexafluorophosphate and lithium bis(fluorosulfonyl)imide are mixed evenly to obtain a second primary electrolyte; VC (vinylene carbonate) and Tppi (triphenyl phosphite) are added to the second primary electrolyte and mixed 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: Contains aluminum foil and active membrane layer, where the active membrane layer contains lithium iron phosphate, conductive agent (conductive carbon black (Super-P)), binder (polyvinylidene fluoride (PVDF)), and lithium supplement agent, with the weight ratio of each component being 93:3:2:2 respectively; the lithium supplement agent is Li5FeO4;

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

[0095] Separator membrane: A polyethylene porous polymer membrane is used as the separator membrane.

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

[0097] The above-mentioned positive electrode sheet, isolation membrane, and negative electrode sheet are assembled according to the designed size and sequence, so that the isolation membrane can completely isolate the positive and negative electrode sheets, and at the same time, the negative electrode sheet can be completely covered with the positive electrode to form a core, which is placed in the outer packaging. After baking until the moisture content is qualified, 35.2g of the prepared first electrolyte is injected and packaged, and it 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 it is allowed to stand at 45°C for 24 hours again for full infiltration. After the electrolytes are mixed, the capacity 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, 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 basically the same as that in Example 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 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 the first electrolyte includes a first solvent, a first lithium salt and a second additive. 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), 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 comprises VC (VOC), FEC (fluoroethylene carbonate), DTD (vinyl sulfate) and DMS (dimethyl sulfide), wherein the mass proportion of the VC in the first electrolyte is 1.8%, the mass proportion of the FEC in the first electrolyte is 0.5%, the mass proportion of the DTD in the first electrolyte is 0.5%, and the mass proportion of the 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 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 by referring 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 basically the same as that in Example 1, except that the mass proportion of the DMS in the first electrolyte is 3%, and the mass proportion of the first solvent in the first electrolyte is 78.7%. 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 the first electrolyte includes a first solvent, a first lithium salt and a second additive. The total mass of the first 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), 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 (vinyl carbonate) The first electrolyte comprises VC (VOC), FEC (fluoroethylene carbonate), DTD (vinyl sulfate) and DMS (dimethyl sulfide), wherein the mass proportion of the VC in the first electrolyte is 1.8%, the mass proportion of the FEC in the first electrolyte is 0.5%, the mass proportion of the DTD in the first electrolyte is 0.5%, and the mass proportion of the DMS in the first electrolyte is 3%; based on the total mass of the second electrolyte being 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 by referring 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 Example 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 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 mass of VC, 0.5% by mass of FEC, 0.5% by mass of DTD and 1% by mass of DMS. The second electrolyte comprises 100% by mass of the second solvent, 74.47% by mass of the second solvent, and the second solvent comprises DMC (dimethyl carbonate). The second electrolyte comprises lithium 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 by referring 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 basically the same as that in Example 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 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 the 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), 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 comprises 1.8% by mass of VC, 0.5% by mass of FEC, 0.5% by mass of DTD and 1% by mass of DMS. The second electrolyte comprises 100% by mass of the second solvent, 74% by mass of the second solvent, and the second solvent comprises 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 by referring 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 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, and the first electrolyte contains The invention relates to a first electrolyte comprising a first solvent, a first lithium salt and a first additive, wherein 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%, and the lithium bisfluorosulfonyl imide is in The mass proportion of the first electrolyte is 3%, and the first additive is composed of VC (vinylene 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%. Taking the total mass of the second electrolyte as 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 by referring 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 by referring 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 as 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 (ethylene 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 by referring 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: Contains aluminum foil and active membrane layer, where the active membrane layer contains lithium iron phosphate, conductive agent (conductive carbon black (Super-P)), binder (polyvinylidene fluoride (PVDF)), and lithium supplement agent, with the weight ratio of each component being 93:3:2:2 respectively; the lithium supplement agent is Li5FeO4;

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

[0128] Separator membrane: A polyethylene porous polymer membrane is used as the separator 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 and the negative electrode sheet, and the negative electrode sheet can be completely covered to form a core, which is placed in an outer package. After baking until the moisture content is qualified, 40g of the prepared electrolyte is injected and packaged. It is left to stand at 45°C for 24 hours to fully infiltrate, and then the formation, overcharge and lithium supplementation, and capacity charging processes are carried out. After the end, a lithium-ion battery with a capacity of 10Ah is obtained by packaging. The formation process includes: at 45 ℃, charging 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: at 45℃, first charging at a constant current of 0.5C to 3.65V, and then charging at a constant current of 0.2C to 4.3V; the differentiated capacity charging process includes: under normal temperature conditions, discharging 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, discharging at a constant current of 0.5C to 2.5V, and finally charging at a constant current of 1C 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 first electrolyte comprises: a first electrolyte containing 1.8% VC, a first electrolyte containing 0.5% FEC, a first electrolyte containing 0.5% DTD, and a first electrolyte containing 0.5% DMS. The second ...

[0133] The electrolyte was prepared by referring 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 bisfluorosulfonyl imide, the mass proportion of lithium hexafluorophosphate in the first electrolyte is 12.5%, the mass proportion of lithium bisfluorosulfonyl imide in the first electrolyte is 3%, and the first additive is VC (ethylene carbonate) The first electrolyte comprises 1.8% by mass of VC, 0.5% by mass of FEC and 0.5% by mass of DTD. Taking the total mass of the second electrolyte as 100%, the mass 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 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 lithium hexafluorophosphate in the second electrolyte is 12.5%, the mass proportion of 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 VC in the second electrolyte is 10%, and the mass proportion of Tppi in the second electrolyte is 0.15%.

[0137] The electrolyte was prepared by referring 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 basically 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 by referring 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 by referring 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 by referring 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 by referring 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 examples and comparative examples was tested, and the specific testing process is as follows:

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

[0158] Capacity-separated 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 condition of the battery negative electrode was observed with the naked eye. The results are shown in Table 1.

[0159] High-temperature gas production: Place the fully charged battery in water at 60°C for a water displacement test (V1). After heating the temperature to 60°C in a constant temperature box and storing for 5 days, take out the battery and place it in water at 60°C for a water displacement test (V2). The volume change is V2-V1. Record the volume change in Table 1. The high-temperature gas production can be 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 a constant current of 1C to 2.5V, obtaining the initial discharge capacity C1. The battery was then fully charged again, raised to 55°C in a constant temperature chamber, and stored for 7 days. The battery was then discharged, fully charged again, and then discharged at a constant current of 1C to 2.5V to obtain the current capacity C2. The capacity recovery rate was 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) 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 high, 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) 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 easily leads to high 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 effects after oxidation, increase the content of vinylene carbonate (VC) in the second electrolyte, and ensure that there is sufficient film-forming additive for the repair of SEI during the later circulation 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) Comparison of Example 1 with Comparative Example 4 shows 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) Comparison of Example 1 with Comparative Example 5 shows that after DMS is replaced with other sulfide compounds, lithium deposition occurs on the negative electrode sheet, 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 above embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the above 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, and the second electrolyte includes a second solvent, a second lithium salt and a second additive, wherein the second electrolyte accounts for 5% to 20% by mass of the electrolyte, the first additive includes dimethyl sulfide and vinylene carbonate, and the second additive includes triphenyl phosphite and vinylene carbonate; Based on the total mass of the first electrolyte being 100%, the mass proportion of the first additive in the first electrolyte is 0.3%-7%; The mass percentage of dimethyl sulfide in the first electrolyte is 0.1-3wt%; The mass percentage of vinylene carbonate in the first additive in the first electrolyte is no more than 2%; 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; The mass percentage of triphenyl phosphite in the second electrolyte is 0.01-0.5%; The mass percentage of vinylene carbonate in the second additive to the second electrolyte is 10% to 30%.

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 each two compounds is (2-5):(2-5); and / or, the first lithium salt comprises 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%, and the mass proportion of the first lithium salt in the first electrolyte is 7%-20%.

3. The electrolyte according to claim 1, characterized in that The first additive further comprises at least one of methylene methanedisulfonate, lithium difluorophosphate, fluoroethylene carbonate, vinyl sulfate, 1,3-propane sultone, tris(trimethylsilane)phosphate, lithium difluorooxalatoborate, and difluorooxalatophosphate.

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. A method for preparing an electrolyte according to any one of claims 1 to 4, characterized in that: The preparation method comprises the following steps: Weighing each component according to the designed ratio, and uniformly mixing the weighed first solvent and the first lithium salt 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.

6. A method for injecting an electrolyte according to any one of claims 1 to 4, characterized in that: The liquid injection method comprises the following steps: The first electrolyte is injected into the battery to be filled and the battery is sealed. After the battery is fully soaked, the formation and overcharge lithium replenishment processes are carried out. Then the second electrolyte is injected and the battery is sealed. The battery is fully soaked again, and the electrolytes are mixed before the capacity-divided charging process is carried out.

7. The electrolyte injection method according to claim 6, characterized in that: The sufficient infiltration includes standing at 20-60° C. for 12-36 hours.

8. A lithium ion battery, characterized in that: The lithium-ion battery comprises the electrolyte according to any one of claims 1 to 4, or is prepared by the injection method according to claim 6 or 7.

9. The lithium-ion battery according to claim 8, characterized in that The lithium-ion battery further comprises a positive electrode sheet, a negative electrode sheet and a separator. The positive electrode sheet comprises a positive electrode current collector and a positive electrode active membrane layer. The positive electrode active membrane layer comprises a lithium supplement agent. The general chemical formula of the lithium supplement agent 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 nickelate, lithium ferrite, and lithium oxide.

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