A lithium-ion battery electrolyte and its application

Abstract

The present invention provides a lithium-ion battery electrolyte and its application. The electrolyte comprises at least the following components: a lithium salt; a solvent; and additives, including a first additive having the general structural formula: wherein R1 and R2 are each selected from a C2-C6 unsaturated chain hydrocarbon group. The lithium-ion battery electrolyte and its application proposed by the present invention can significantly improve the cycle life of the lithium-ion battery while ensuring that the initial impedance and high-temperature storage performance of the lithium-ion battery are not affected.

Description

Technical Field

[0001] The present invention relates to the technical field of power batteries, and in particular to a lithium-ion battery electrolyte and applications thereof. Background Art

[0002] As a type of lithium-ion battery, cylindrical batteries have the advantages of high single-cell consistency, good heat dissipation, high production yield and high automation efficiency, making them the first choice for power batteries for electric vehicles. Among them, the chemical system that matches the high-nickel ternary positive electrode and the silicon-doped graphite negative electrode can compensate for the capacity density of the single cell to ensure the requirements of the cylindrical battery for high energy density and group efficiency. However, in actual applications, due to the volume expansion effect of the silicon-doped graphite negative electrode, on the one hand, the electrolyte is squeezed to the upper and lower ends of the battery column, and the middle section of the pole roll is prone to lithium precipitation due to local poor liquid, resulting in degradation of the battery performance. On the other hand, the solid electrolyte interface (SEI) film is damaged, and in the process of continuous repair and proliferation of the SEI film, the interface impedance increases and the risk of lithium precipitation at the negative electrode is aggravated, which also degrades the cycle capacity of the battery. Therefore, for cylindrical batteries with high nickel and silicon high energy density systems, short cycle life is the main defect. Summary of the Invention

[0003] The present invention proposes a lithium-ion battery electrolyte and its application. The lithium-ion battery electrolyte and its application provided by the present invention can significantly improve the cycle life of the battery while ensuring that the initial impedance and high-temperature storage performance of the lithium-ion battery are not affected.

[0004] To solve the above technical problems, the present invention provides a lithium-ion battery electrolyte comprising at least the following components:

[0005] lithium salts;

[0006] solvents; and

[0007] Additives, wherein the additives include a first additive, and the general structural formula of the first additive is:

[0008]

[0009] Wherein, R1 and R2 are each selected from a C2-C6 unsaturated chain hydrocarbon group.

[0010] In one embodiment of the present invention, R1 and R2 have the same structure, and / or R1 and R2 are C2-C6 alkenyl groups.

[0011] In one embodiment of the present invention, the first additive is selected from:

[0012] At least one of .

[0013] In one embodiment of the present invention, the content of the first additive in the electrolyte is 0.01 wt %-1 wt %.

[0014] In one embodiment of the present invention, the solvent includes a first solvent, the first solvent includes a carboxylic acid ester, the carboxylic acid ester is selected from at least one of methyl acetate, ethyl acetate or ethyl propionate, and the content of the first solvent in the electrolyte is 2wt%-15wt%.

[0015] In one embodiment of the present invention, the solvent also includes a second solvent, the second solvent includes cyclic esters and chain esters, the cyclic esters are selected from at least one of ethylene carbonate or propylene carbonate, and the content of the cyclic esters in the electrolyte is 8wt%-24wt%, the chain esters are selected from at least one of ethyl methyl carbonate or dimethyl carbonate, and the content of the chain esters in the electrolyte is 40wt%-70wt%.

[0016] In one embodiment of the present invention, the lithium salt includes lithium hexafluorophosphate, and the content of the lithium salt in the electrolyte is 14 wt %-17 wt %.

[0017] In one embodiment of the present invention, the electrolyte further comprises fluoroethylene carbonate, and the content of the fluoroethylene carbonate in the electrolyte is 2 wt % to 10 wt %.

[0018] In one embodiment of the present invention, the additive further includes a second additive, the second additive being selected from at least one of vinylene carbonate, vinyl sulfate, 1,3-propane sultone, lithium difluorooxalatophosphate or lithium difluorooxalatoborate, and the content of each second additive in the electrolyte is 0.1 wt%-1.5 wt%.

[0019] The present invention also provides a lithium ion battery, comprising at least:

[0020] The positive electrode sheet includes a positive electrode active material, wherein the positive electrode active material has the structural formula of Li x [Ni y Co z Mn t M (1-y-z-t) ]O 2-δ , wherein M is selected from at least one of Cr, Zr, Ca, Mg, Cu, Ti, Al, Mo, W and Zn, 0.9 <x<1.1,0.9≤y<1.0,0≤z<0.1,0≤t<0.1,0≤δ≤0.1;

[0021] A negative electrode plate, comprising a negative electrode active material, wherein the negative electrode active material is selected from at least one of a graphite-doped silicon-oxygen material and a graphite-doped silicon-carbon material;

[0022] a separator, disposed between the positive electrode sheet and the negative electrode sheet; and

[0023] The electrolyte is selected from the above-mentioned lithium ion battery electrolyte.

[0024] In one embodiment of the present invention, in the negative electrode active material, the doping content of the silicon-oxygen material or the silicon-carbon material is 1 wt %-10 wt %.

[0025] In summary, the present invention proposes a lithium-ion battery electrolyte and its application. On the one hand, it can improve the mechanical strength and stability of the SEI film, inhibit the volume expansion of the silicon-doped negative electrode, and reduce the interface impedance degradation and the risk of negative electrode lithium plating caused by continuous damage and repair growth of the SEI film. On the other hand, it can effectively reduce the viscosity of the electrolyte, improve the wettability of the electrolyte to the electrode, and reduce the risk of negative electrode lithium plating. The above two aspects work together to significantly improve the cycle life of the lithium-ion battery. It can also significantly improve the cycle life of the battery while ensuring that the initial impedance and high-temperature storage performance of the battery are not affected. DETAILED DESCRIPTION

[0026] The following describes the embodiments of the present invention through specific examples. Those skilled in the art will readily understand the other advantages and benefits of the present invention from the disclosure herein. The present invention may also be implemented or applied through various other specific embodiments, and the details in this specification may be modified or altered based on different viewpoints and applications without departing from the spirit of the present invention.

[0027] It should be understood that the present invention can be implemented in different forms and should not be interpreted as being limited to the embodiments set forth herein. On the contrary, these embodiments are provided to make disclosure thorough and complete and to fully convey the scope of the present invention to those skilled in the art.

[0028] The technical solutions of the present invention are further described in detail below with reference to the embodiments. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0029] The present invention provides a lithium-ion battery electrolyte comprising at least a lithium salt, a solvent, and an additive, wherein the additive comprises a first additive having a general structural formula of: wherein R1 and R2 are each selected from a C2-C6 unsaturated chain hydrocarbon group. In the lithium-ion battery electrolyte provided by the present invention, by introducing the first additive, the mechanical strength and stability of the SEI film can be improved, the volume expansion of the silicon-doped negative electrode can be suppressed, and the risk of interfacial impedance degradation and negative electrode lithium plating caused by continuous damage and repair growth of the SEI film can be reduced, thereby extending the service life of the lithium-ion battery.

[0030] In one embodiment of the present invention, the first additive is, for example, a fluorobissulfonamide compound, wherein R1 and R2 have the same structure, and / or R1 and R2 are, for example, C2-C6 alkenyl groups. Specifically, in this embodiment, the first additive is, for example, selected from: At least one of the following. By introducing the first additive, due to the unsaturated bonds in the functional groups of R1 and R2, the first additive is easily subjected to a reaction of first adsorption and then polymerization at the negative electrode interface. At the same time, the NF bonds in the first additive will be partially broken due to the low bond energy. The partially broken fluoride ions can form LiF inorganic products on the surface of the silicon negative electrode, which helps to form a SEI film interwoven with organic and inorganic components, effectively improving the mechanical strength and stability of the SEI film, and inhibiting the volume expansion of the silicon-doped negative electrode during the cycle. This can reduce the interface impedance degradation and the risk of lithium plating on the negative electrode caused by continuous damage and repair proliferation of the SEI film, thereby improving the cycle life of the battery.

[0031] In one embodiment of the present invention, the content of the first additive in the electrolyte is, for example, 0.01 wt%-1 wt%, and further, for example, 0.05 wt%-0.5 wt%. By controlling the content of the first additive, the degree to which the first additive affects the initial impedance of the battery can be reduced.

[0032] In one embodiment of the present invention, the additive further includes a second additive, and the second additive is selected from at least one of vinylene carbonate (VC), vinyl sulfate (DTD), 1,3-propane sultone (PS), lithium difluoro oxalophosphate (LiODFP) or lithium difluoro oxaloborate (LiODFB), and the content of each second additive in the electrolyte is, for example, 0.1wt%-1.5wt%. Further, the second additive includes, for example, at least one of VC, LiODFP or LiODFB, and the content of each second additive in the electrolyte is, for example, 0.1wt%-0.5wt%, and the content of each additive in the electrolyte can be equal or unequal. By introducing the second additive into the electrolyte, the composition of the SEI film can be optimized to form a stable and dense SEI film, thereby suppressing the occurrence of side reactions on the electrode surface, increasing the initial discharge capacity of the lithium-ion battery, improving the high and low temperature storage performance of the lithium-ion battery, and improving the high temperature cycle performance of the lithium-ion battery.

[0033] In one embodiment of the present invention, the solvent includes a first solvent, which includes, for example, a carboxylate, which is selected from at least one of methyl acetate (MA), ethyl acetate, or ethyl propionate, and the content of the first solvent in the electrolyte is, for example, 2wt%-15wt%, and further, for example, 4wt%-8wt%. By introducing a first solvent of the carboxylate class, the viscosity of the electrolyte can be effectively reduced and the conductivity of the electrolyte can be increased, thereby effectively reducing the initial impedance of the battery. At the same time, when the pressure between the pole coil layers in the middle section of the battery column is high, the electrolyte still has a high wettability to the pole piece, maintaining an effective electrolyte path, thereby reducing the risk of lithium plating at the negative electrode and further improving the cycle life of the battery. Moreover, the first solvent and the first additive can achieve a complementary effect, significantly improving the cycle life of the battery while ensuring that the initial impedance and high-temperature storage performance of the battery are not affected. Moreover, by controlling the content of the first solvent, the degree to which the high-temperature cycle performance of the battery is affected by the first solvent can be alleviated.

[0034] In one embodiment of the present invention, the solvent further includes a second solvent, which includes cyclic esters and chain esters. The cyclic ester is selected from at least one of ethylene carbonate (EC) and propylene carbonate, and the content of the cyclic ester in the electrolyte is, for example, 8 wt% to 24 wt%. The chain ester is selected from at least one of ethyl methyl carbonate (EMC) and dimethyl carbonate (DMC), and the content of the chain ester in the electrolyte is, for example, 40 wt% to 70 wt%. Specifically, in this embodiment, the cyclic ester includes EC, and the chain ester includes EMC and DMC, and the content of EC in the electrolyte is, for example, 16 wt%, and the total content of EMC and DMC in the electrolyte is, for example, 43 wt% to 63 wt%. By controlling the content of the second solvent, while maintaining the electrolyte's performance, the electrolyte can be prevented from being excessively high, which could lead to excessive viscosity and reduced ionic conductivity and wettability.

[0035] In one embodiment of the present invention, the lithium salt includes, for example, lithium hexafluorophosphate (LiPF 6 ), and the content of the lithium salt in the electrolyte is, for example, 14 wt % to 17 wt %.

[0036] In one embodiment of the present invention, the electrolyte further includes fluoroethylene carbonate (FEC), and the content of FEC in the electrolyte is, for example, 2wt% to 10wt%. The addition of FEC decomposes to form fluoride ions, which react with lithium salts in the solvent to produce LiF, which is resistant to decomposition and has excellent insulating properties. This helps form a uniform, dense, low-impedance, and highly elastic SEI film, thereby improving the cycle life of the battery.

[0037] In one embodiment of the present invention, when preparing the electrolyte, in a glove box with a stable gas atmosphere such as argon, a first solvent and a second solvent are mixed uniformly in a certain mass ratio, and then a fully dried lithium salt is added to the solvent. Furthermore, the first additive, the second additive, and FEC are added to prepare a lithium-ion battery electrolyte. The moisture content in the glove box is, for example, less than 10 ppm.

[0038] The present invention also provides a lithium-ion battery, which may be a primary battery or a secondary battery, and a secondary battery may be a soft-pack battery, a hard-shell battery, or a cylindrical battery. The present invention does not specifically limit the type and type of lithium-ion batteries. The present invention uses cylindrical batteries as an example to illustrate lithium-ion batteries. In this embodiment, the lithium-ion battery includes a housing and a bare cell disposed within the housing, wherein the bare cell includes a positive electrode sheet, a separator, a negative electrode sheet, and an electrolyte. The separator is located between the positive electrode sheet and the negative electrode sheet to prevent a short circuit between the positive electrode sheet and the negative electrode sheet, allowing lithium ions to pass through. The electrolyte is filled between the positive electrode sheet, the separator, and the negative electrode sheet, and the electrolyte is the above-mentioned lithium-ion battery electrolyte, which acts as an ion conductor.

[0039] In one embodiment of the present invention, the positive electrode sheet includes a positive electrode current collector and a positive electrode active layer coated on at least one surface of the positive electrode current collector. The positive electrode current collector is, for example, a foil formed by surface treatment of nickel, titanium, aluminum, nickel, silver, stainless steel, or carbon. In addition to foil, the positive electrode current collector may also be in the form of a film, mesh, porous material, foam, or non-woven fabric, among other forms, or any combination thereof.

[0040] In one embodiment of the present invention, the positive electrode active layer includes a positive electrode active material, a conductive agent, and a binder. The ratio of the positive electrode active material, the conductive agent, and the binder can be selected according to actual needs. In this embodiment, the positive electrode active material is, for example, a high nickel ternary material, whose chemical formula is, for example, Li x [Ni y Co z Mn t M (1-y-z-t) ]O 2-δ , wherein M is selected from at least one of Cr, Zr, Ca, Mg, Cu, Ti, Al, Mo, W or Zn, etc., 0.9 <x<1.1,0.9≤y<1.0,0≤z<0.1,0≤t<0.1,0≤δ≤0.1。

[0041] In one embodiment of the present invention, the conductive agent is, for example, selected from at least one of conductive carbon black (SuperP), acetylene black, carbon nanotubes, or graphene, and the binder is, for example, selected from at least one of polyvinylidene fluoride (PVDF), polyethylene oxide (PEO), polyamide (PA), polyacrylonitrile (PAN), polyacrylate, polyvinylether, polymethyl methacrylate (PMMA), ethylene-propylene-diene terpolymer (EPDM), polyhexafluoropropylene, or styrene-butadiene rubber (SBR).

[0042] In one embodiment of the present invention, the positive electrode current collector is, for example, aluminum foil, and the positive electrode active material is, for example, LiNi 0.9 Mn 0.05 Co 0.05 O2, a conductive agent such as conductive carbon black, and a binder such as polyvinylidene fluoride. The positive electrode active material, conductive agent, and binder are mixed in a mass ratio of, for example, 97:1:2, dissolved in an organic solvent, and stirred in a vacuum mixer until the system is uniform to obtain a positive electrode slurry. The positive electrode slurry is then evenly coated on aluminum foil, dried at room temperature, and then transferred to an oven for drying. The positive electrode sheet is obtained through cold pressing, trimming, cutting, and slitting. The organic solvent is, for example, N-methylpyrrolidone (NMP).

[0043] In one embodiment of the present invention, the negative electrode plate includes, for example, a negative electrode current collector and a negative electrode active layer coated on at least one surface of the negative electrode current collector. The negative electrode current collector is, for example, selected from a copper foil current collector, a composite copper foil current collector, a carbon current collector, a foam copper current collector, or a stainless steel current collector.

[0044] In one embodiment of the present invention, the negative electrode active layer includes a negative electrode active material, a conductive agent, a binder, and a thickener. The ratio of the negative electrode active material, conductive agent, binder, and thickener can be selected based on actual needs. In this embodiment, the negative electrode active material is selected from at least one of a graphite-doped silicon-oxygen material or a graphite-doped silicon-carbon material. The silicon-oxygen material or silicon-carbon material may be doped in the negative electrode active material at a content of, for example, 1 wt% to 10 wt%.

[0045] In one embodiment of the present invention, the binder is selected from at least one of PVDF, PEO, PA, polypropylene, polyacrylate, polyvinyl ether, PMMA, polyhexafluoropropylene, and SBR. The thickener is selected from at least one of carboxymethyl cellulose sodium (CNC-Na). The conductive agent is selected from at least one of conductive carbon black, acetylene black, Ketjen black, carbon nanotubes, and graphene.

[0046] In one embodiment of the present invention, the negative electrode current collector is, for example, copper foil, the negative electrode active material is, for example, graphite-doped silicon oxide material, and the doping content of silicon oxide material in the negative electrode active material is, for example, 3wt%, the doping content of graphite material in the negative electrode active material is, for example, 97wt%, the conductive agent is, for example, conductive carbon black, the thickener is, for example, CNC-Na, and the binder is, for example, SBR. Specifically, the negative electrode active material, the conductive agent, the thickener, and the binder carbon are mixed in a mass ratio of 96.5:1:1:1.5, and deionized water solvent is added, and then the mixture is thoroughly stirred and mixed under the action of a vacuum mixer to obtain a negative electrode slurry, which is coated on a copper foil, and then transferred to an oven for drying after drying at room temperature. After cold pressing, trimming, cutting, and slitting, a negative electrode sheet is obtained.

[0047] In one embodiment of the present invention, the separator is, for example, a conventional separator, a ceramic separator, a polymer separator, a non-woven fabric, or an inorganic-organic composite separator. Specifically, the separator is, for example, a single-layer polypropylene (PP) film, a single-layer polyethylene (PE) film, a double-layer PP / PE film, a double-layer PP / PP film, or a triple-layer PP / PE / PP film. In this embodiment, a single-layer PP film is selected as the separator.

[0048] In one embodiment of the present invention, the above-mentioned positive electrode sheet, separator and negative electrode sheet are placed in sequence, so that the separator is placed between the positive electrode sheet and the negative electrode sheet to play an isolating role. A multi-layer laminate is obtained by winding and loaded into a battery casing as a bare cell. Then, the above-prepared lithium-ion battery electrolyte is injected into the casing once or multiple times so that the bare cell is completely immersed in the electrolyte to obtain a cylindrical battery.

[0049] Hereinafter, the present invention will be explained in more detail by citing examples, which should not be construed as limiting. Appropriate modifications may be made within the scope consistent with the gist of the present invention, all of which fall within the technical scope of the present invention.

[0050] Example 1

[0051] Preparation of positive electrode: LiNi 0.9 Mn 0.05 Co 0.05O2, conductive carbon black and polyvinylidene fluoride are mixed in a mass ratio of 97:1:2, dissolved in NMP organic solvent, and stirred under the action of a vacuum mixer until the system becomes uniform to obtain a positive electrode slurry. The positive electrode slurry is then evenly coated on aluminum foil, and then transferred to an oven for drying after drying at room temperature. The positive electrode sheet is obtained through processes such as cold pressing, trimming, cutting and slitting.

[0052] Preparation of the negative electrode sheet: A silicon oxide material and a graphite material are uniformly mixed to obtain a negative electrode active material, wherein the silicon oxide material has a doping content of 3wt% and the graphite material has a doping content of 97wt%. The negative electrode active material, conductive carbon black, CNC-Na, and SBR are mixed in a mass ratio of 96.5:1:1:1.5, and deionized water is added. The mixture is then thoroughly stirred and mixed in a vacuum mixer to obtain a negative electrode slurry. The slurry is then coated onto copper foil, air-dried at room temperature, and then oven-dried. The negative electrode sheet is obtained through cold pressing, trimming, cutting, and slitting.

[0053] Preparation of the electrolyte: In an argon atmosphere glove box with a moisture content of less than 1 ppm, the second solvent EC, EMC, and DMC were uniformly mixed according to the electrolyte composition described in Table 1 to obtain a solvent. Thoroughly dried LiPF6 was then added to the solvent, and the first additive, Compound 1, was added and mixed uniformly to prepare a lithium-ion battery electrolyte. The contents of LiPF6 and Compound 1 in the electrolyte were 15 wt% and 0.01 wt%, respectively.

[0054] Selection of diaphragm: Choose single-layer PP film as the diaphragm.

[0055] Preparation of the battery: The positive electrode sheet, separator and negative electrode sheet are placed in sequence, and a multi-layer laminate is obtained by winding. The laminate is then loaded into a battery casing as a bare cell. The electrolyte prepared above is then injected into the casing so that the bare cell is completely immersed in the electrolyte to obtain a cylindrical battery.

[0056] Example 2

[0057] The contents of compound 1 and DMC in the electrolyte were 0.05 wt % and 60.95 wt %, respectively. Other steps were the same as those in Example 1.

[0058] Example 3

[0059] The contents of compound 1 and DMC in the electrolyte were 0.2 wt % and 60.8 wt %, respectively. Other steps were the same as those in Example 1.

[0060] Example 4

[0061] The contents of compound 1 and DMC in the electrolyte were 0.5 wt % and 60.5 wt %, respectively. Other steps were the same as those in Example 1.

[0062] Example 5

[0063] The contents of compound 1 and DMC in the electrolyte were 1 wt % and 60 wt %, respectively. Other steps were the same as those in Example 1.

[0064] Example 6

[0065] The electrolyte contains the first solvent MA, and the contents of MA, compound 1 and DMC in the electrolyte are 2 wt %, 0.2 wt % and 58.8 wt %, respectively. Other steps are the same as those in Example 1.

[0066] Example 7

[0067] The contents of MA and DMC in the electrolyte were 4 wt % and 56.8 wt %, respectively. Other steps were the same as those in Example 6.

[0068] Example 8

[0069] The contents of MA and DMC in the electrolyte were 8 wt % and 52.8 wt % respectively. Other steps were the same as those in Example 6.

[0070] Example 9

[0071] The contents of MA and DMC in the electrolyte were 15 wt % and 45.8 wt %, respectively. Other steps were the same as those in Example 6.

[0072] Example 10

[0073] The electrolyte contains FEC, and the contents of FEC, compound 1 and DMC in the electrolyte are 2 wt %, 0.2 wt % and 58.8 wt %, respectively. Other steps are the same as those in Example 1.

[0074] Example 11

[0075] The contents of FEC, compound 1 and DMC in the electrolyte were 5 wt %, 0.2 wt % and 55.8 wt %, respectively. Other steps were the same as in Example 10.

[0076] Example 12

[0077] The contents of FEC, compound 1 and DMC in the electrolyte were 10 wt %, 0.2 wt % and 50.8 wt %, respectively. Other steps were the same as in Example 10.

[0078] Example 13

[0079] The electrolyte contains DTD, and the contents of DTD and DMC in the electrolyte are 1 wt % and 59.8 wt % respectively. Other steps are the same as those in Example 3.

[0080] Example 14

[0081] The electrolyte contains MA, FEC, DTD and compound 1 at the same time. The contents of MA, FEC, DTD, compound 1 and DMC in the electrolyte are 8wt%, 5wt%, 1wt%, 0.2wt% and 46.8wt%, respectively. The other steps are the same as in Example 1.

[0082] Comparative Example 1

[0083] The contents of compound 1 and DMC in the electrolyte were 0 and 61 wt %, respectively. Other steps were the same as those in Example 6.

[0084] Comparative Example 2

[0085] The electrolyte contains MA, and the contents of MA and DMC in the electrolyte are 2 wt % and 59 wt % respectively. Other steps are the same as those in Comparative Example 1.

[0086] Comparative Example 3

[0087] The electrolyte contains FEC, and the contents of FEC and DMC in the electrolyte are 2 wt % and 59 wt % respectively. Other steps are the same as those in Comparative Example 1.

[0088] Comparative Example 4

[0089] The electrolyte contains DTD, and the contents of DTD and DMC in the electrolyte are 1 wt % and 60 wt % respectively. Other steps are the same as those in Comparative Example 1.

[0090] Comparative Example 5

[0091] The electrolyte contains FN(SO2CH3)2, and the contents of compound 1 and FN(SO2CH3)2 in the electrolyte are 0 and 0.2 wt% respectively. The other steps are the same as those in Example 3.

[0092] The raw material component contents and raw material mass ratios required for the electrolytes prepared in the examples and comparative examples are shown in Table 1. The content of each component is the mass percentage calculated based on the total mass of the electrolyte.

[0093] Table 1. Composition of the electrolyte in Examples 1-14 and Comparative Examples 1-5

[0094]

[0095] In the present invention, performance tests were conducted on lithium-ion batteries prepared using different electrolyte ratios in Examples 1-14 and Comparative Examples 1-5. The test results are shown in Table 2.

[0096] In one embodiment of the present invention, for example, an initial BOL (Beginning of Life) direct current resistance (DCR) test is performed on a lithium-ion battery. Specifically, the temperature of the thermostat is adjusted to 25°C, and the lithium-ion battery is allowed to stand in the thermostat for 10 minutes. The battery is then charged to 4.25V at a constant current of 0.33C, and then charged to 0.05C at a voltage of 4.25V. After standing for 30 minutes, the battery is then discharged to 2.5V at a constant current of 0.33C, and allowed to stand for 10 minutes. This cycle is repeated twice to obtain the last discharge capacity C0. The battery is then charged to 4.25V at a constant current of 0.33C, and then charged to 0.05C at a constant voltage. After standing for 30 minutes, the battery is discharged to (50% C0) at a constant current of 0.33C, and allowed to stand for 1 hour. The static terminal voltage V0 is recorded. The battery is then discharged at a constant current of 2C for 10 seconds, and the voltage V1 is recorded. The BOL DCR is calculated according to the following formula:

[0097] BOL DCR=(V0-V1) / current value;

[0098] The current value is the current value when the battery is discharged at a constant current of 2C.

[0099] In one embodiment of the present invention, for example, a normal temperature cycle life test is performed on a lithium-ion battery. Specifically, the constant temperature of the thermostat is adjusted to 25°C, and the lithium-ion battery is stabilized in the thermostat for 30 minutes. Then, it is charged to 4.25V at a constant current of 0.5C, and then charged to 0.05C at a constant voltage. After standing for 10 minutes, it is discharged to 2.5V at a constant current of 0.5C. After this charge and discharge process is cycled 800 times, the discharge capacity C1 of the battery cell at the end of the 800th discharge cycle is recorded. The cycle capacity retention rate of the battery cycled 800 times at 25°C is calculated according to the following formula:

[0100] Cycle capacity retention rate (%) = C1 / C0×100%.

[0101] In one embodiment of the present invention, for example, a high-temperature storage performance test is performed on a lithium-ion battery. Specifically, the temperature of the thermostat is adjusted to 25°C, and the lithium-ion battery is allowed to stand in the thermostat for 10 minutes. It is then charged to 4.25V at a constant current of 0.33C, and then charged to 0.05C at a voltage of 4.25V. After standing for 30 minutes, it is discharged to 2.5V at a constant current of 0.33C, and allowed to stand for 10 minutes. This cycle is repeated twice, and the last discharge capacity is taken as C2. The battery is then transferred to a thermostat at 55°C and stored for 90 days. Within 90 days, the battery is recharged every 15 days. Specifically, each time the battery is recharged, the battery is transferred to a thermostat at 25°C and allowed to stand for 2 hours. It is then charged to 4.25V at a constant current of 0.33C, and then charged to 0.05C at a voltage of 4.25V. It is then transferred back to a thermostat at 55°C for continued storage. After 90 days of storage, repeat the above 0.33C charge and discharge operation three times on the battery, record the last discharge capacity as C3, and calculate the storage capacity retention rate according to the following formula:

[0102] Storage capacity retention rate = C3 / C2×100%.

[0103] Table 2. Performance test results of lithium-ion batteries in Examples 1-14 and Comparative Examples 1-5

[0104]

[0105] Please refer to Table 1 and Table 2. Comparison of Example 3, Comparative Example 1 and Comparative Example 5 shows that when FN(SO2CH3)2 and Compound 1 are compared, when Compound 1 is contained in the electrolyte, the BOL DCR, cycle capacity retention rate and storage capacity retention rate of the battery are significantly increased, and the increase is higher, indicating that the introduction of Compound 1 can effectively improve the stability of the SEI film of the silicon negative electrode, inhibit the volume expansion of the negative electrode and the increase in the internal pressure of the pole coil during the cycle, which causes the local slight lithium precipitation of the negative electrode, thereby effectively improving the cycle life and high-temperature storage performance of the battery. However, the polymerization of the double bond in Compound 1 into a film also increases the initial SEI film thickness to a certain extent, resulting in the BOL DCR being affected. Therefore, while Compound 1 improves the cycle life and high-temperature storage performance of the battery, it also affects the initial impedance of the battery.

[0106] As shown in Tables 1 and 2, a comparison of Examples 1-5 shows that as the content of Compound 1 in the electrolyte increases, the battery's BOL DCR, cycle capacity retention rate, and storage capacity retention rate all significantly increase. This indicates that, although the battery's initial impedance is affected as the content of Compound 1 increases, the cycle life and high-temperature storage performance are significantly improved. Therefore, by controlling the content of Compound 1, the battery's initial impedance, cycle life, and high-temperature storage performance can be balanced.

[0107] Please refer to Table 1 and Table 2. By comparing Comparative Examples 1-2 and Examples 3 and 6, it can be seen that when the electrolyte contains MA, the BOL DCR and storage capacity retention rate of the battery are reduced, and the cycle capacity retention rate is increased, which shows that the introduction of MA can effectively reduce the viscosity of the electrolyte and increase the conductivity of the electrolyte, thereby effectively reducing the initial impedance of the battery. At the same time, it can improve the wettability of the electrolyte to the electrode after the internal pressure of the electrode roll increases during the cycle process, maintain an effective electrolyte path, and reduce the risk of local lithium precipitation at the negative electrode, thereby effectively improving the cycle life of the battery. However, due to the poor high-temperature stability of MA itself, the side reaction between MA and the positive electrode interface is aggravated, which affects the high-temperature storage performance of the battery. Therefore, while MA improves the BOL DCR and cycle life of the battery, it also affects the high-temperature storage performance.

[0108] As shown in Tables 1 and 2, by comparing Example 3, Example 6, and Comparative Examples 1-2, it can be seen that when the electrolyte contains both MA and Compound 1, the battery's BOL DCR does not increase significantly, while the cycle capacity retention rate and storage capacity retention rate increase significantly. This indicates that: MA can alleviate the extent to which Compound 1 affects the initial impedance of the battery while maintaining the optimization effect of Compound 1 on cycle life; Compound 1 can alleviate the extent to which MA affects the high-temperature storage performance while maintaining the optimization effect of MA on cycle life; and MA and Compound 1 work together to further improve the cycle life of the battery. Therefore, MA and Compound 1 can achieve complementary effects, significantly improving the cycle life of the battery while ensuring that the initial impedance and high-temperature storage performance of the battery are not affected.

[0109] As shown in Table 1 and Table 2, it can be seen from the comparison of Examples 6-9 that as the MA content in the electrolyte increases, the battery's BOL DCR and storage capacity retention rate decrease, while the cycle capacity retention rate increases. This shows that: as the MA content increases, although the battery's initial impedance and cycle life performance are improved, due to the poor high-temperature stability of MA itself, when its content is high, the side reaction between MA and the positive electrode interface is intensified, resulting in an increase in the loss of battery storage capacity, thereby affecting the battery's high-temperature storage performance. Therefore, by controlling the MA content, the battery's initial impedance, cycle life, and high-temperature storage performance can be taken into account.

[0110] As shown in Tables 1 and 2, a comparison of Comparative Examples 1 and 3 shows that the introduction of FEC into the electrolyte increases the battery's BOL DCR and cycle capacity retention, while decreasing the storage capacity retention. This indicates that FEC participates in the repair and film formation of the negative electrode SEI, thereby improving the battery's cycle stability and cycle life. However, this affects the initial impedance. Furthermore, the introduction of FEC exacerbates the acidification of the electrolyte during high-temperature storage, affecting the battery's high-temperature storage performance. Therefore, the introduction of FEC into the electrolyte can improve the battery's cycle life.

[0111] As shown in Tables 1 and 2, by comparing Example 3, Example 10, Comparative Example 1, and Comparative Example 3, it can be seen that when the electrolyte contains both FEC and Compound 1, although the BOL DCR of the battery increases, the cycle capacity retention rate and storage capacity retention rate increase. This indicates that: when FEC is used alone, the high-temperature storage performance of the battery is affected, but Compound 1 can offset the negative impact of FEC on the high-temperature storage performance. At the same time, Compound 1 and FEC work synergistically to further improve the high-temperature storage performance. Moreover, the synergistic effect of Compound 1 and FEC can further improve the cycle life. Therefore, Compound 1 and FEC work synergistically to further improve the high-temperature storage performance and cycle life of the battery.

[0112] As shown in Tables 1 and 2, a comparison of Examples 10-12 shows that as the FEC content in the electrolyte increases, the battery's BOL DCR and cycle capacity retention increase, while the storage capacity retention decreases. This indicates that increasing the FEC content affects the battery's initial film formation impedance and exacerbates electrolyte acidification during high-temperature storage, resulting in a decrease in high-temperature storage performance. However, during the cycle, FEC's SEI repair effect continues to increase, thereby improving the battery's cycle life. Therefore, by controlling the FEC content, the battery's cycle life can be improved without significantly affecting its initial impedance and high-temperature storage performance.

[0113] As shown in Table 1 and Table 2, by comparing Comparative Example 1 and Comparative Example 4, it can be seen that after adding DTD to the electrolyte, the BOL DCR of the battery increases slightly, the cycle capacity retention rate remains basically unchanged, and the storage capacity retention rate increases significantly, indicating that DTD participates in strengthening the initial film formation, and the introduction of sulfate inorganic components improves the high-temperature stability and the high-temperature storage performance of the battery. At the same time, its film-forming organic component is similar to polyethylene oxide (PEO) and has good ion conductivity, and the initial film formation impedance is not greatly affected.

[0114] As shown in Tables 1 and 2, a comparison of Example 3, Example 13, Comparative Example 1, and Comparative Example 4 shows that when the electrolyte contains both DTD and Compound 1, although the battery's BOL DCR increases and the cycle capacity retention rate is essentially the same as when Compound 1 alone is contained in the electrolyte, the storage capacity retention rate significantly increases. This indicates that DTD and Compound 1 act synergistically to further enhance the battery's high-temperature stability and improve its high-temperature storage performance while maintaining the cycle life-enhancing effect of Compound 1. Therefore, DTD and Compound 1 act synergistically to further improve the battery's high-temperature storage performance while extending the battery's cycle life.

[0115] As shown in Tables 1 and 2, by comparing Examples 3, 8, 11, 13-14, and Comparative Example 1, it can be seen that when the electrolyte contains MA, FEC, DTD, and Compound 1 at the same time, the BOL DCR of the battery is not large, and the cycle capacity retention rate and the storage capacity retention rate are maintained at a large value, indicating that when the electrolyte contains MA, FEC, DTD, and Compound 1 at the same time, the initial impedance, high-temperature storage performance, and cycle life of the battery can be comprehensively improved.

[0116] The present invention also provides an electronic device, which includes at least one of the above-mentioned lithium-ion batteries, and the lithium-ion battery is used to provide electrical energy. The electronic device may be a vehicle, a mobile phone, a portable device, a laptop computer, a ship, a spacecraft, an electric toy, and an electric tool, etc. In one embodiment of the present invention, the vehicle is, for example, a new energy vehicle, which may be a pure electric vehicle, a hybrid vehicle, or an extended-range vehicle, etc. The spacecraft includes airplanes, rockets, space shuttles, and spacecraft, etc. The electric toys include fixed or mobile electric toys, such as game consoles, electric car toys, electric ship toys, and electric airplane toys, etc. The electric tools include metal cutting electric tools, grinding electric tools, assembly electric tools, and railway electric tools, such as electric drills, electric grinders, electric wrenches, electric screwdrivers, electric hammers, impact drills, concrete vibrators, and electric planers, etc. The electronic device includes the above-mentioned lithium-ion battery, and therefore includes the advantages of the above-mentioned lithium-ion battery, which will not be elaborated on here.

[0117] In summary, the present invention proposes a lithium-ion battery electrolyte and its application. By introducing a first additive into the electrolyte, the mechanical strength and stability of the SEI film can be improved, the volume expansion of the silicon-doped negative electrode can be suppressed, and the interface impedance degradation and the risk of negative electrode lithium plating caused by continuous damage and repair proliferation of the SEI film can be reduced, thereby improving the cycle life of the lithium-ion battery. By introducing a first solvent into the electrolyte, the viscosity of the electrolyte can be effectively reduced, the wettability of the electrolyte to the electrode can be improved, and the risk of negative electrode lithium plating can be reduced, thereby further improving the cycle life of the lithium-ion battery. Moreover, the first additive and the first solvent can achieve a complementary effect, significantly improving the cycle life of the battery while ensuring that the initial impedance and high-temperature storage performance of the battery are not affected.

[0118] The above description is only a preferred embodiment of the present application and an explanation of the technical principles used. Those skilled in the art should understand that the scope of the invention involved in this application is not limited to the technical solutions formed by the specific combination of the above-mentioned technical features, but should also cover other technical solutions formed by any combination of the above-mentioned technical features or their equivalent features without departing from the inventive concept, such as the technical solutions formed by the mutual replacement of the above-mentioned features with (but not limited to) technical features with similar functions disclosed in this application.

[0119] Except for the technical features described in the specification, the remaining technical features are known technologies to those skilled in the art. In order to highlight the innovative features of the present invention, the remaining technical features will not be described here in detail.

Claims

1. A lithium ion battery electrolyte, characterized in that At least the following components: lithium salts; solvents; as well as Additives, wherein the additives include a first additive, and the general structural formula of the first additive is: Wherein, R1 and R2 are each selected from a C2-C6 unsaturated chain hydrocarbon group.

2. The lithium-ion battery electrolyte according to claim 1, characterized in that R1 and R2 have the same structure, and / or R1 and R2 are C2-C6 alkenyl.

3. The lithium-ion battery electrolyte according to claim 1, characterized in that The first additive is selected from: Compound 1 or At least one of compound 2.

4. The lithium-ion battery electrolyte according to claim 1, characterized in that The content of the first additive in the electrolyte is 0.01 wt%-1 wt%.

5. The lithium-ion battery electrolyte according to claim 1, characterized in that The solvent includes a first solvent, the first solvent includes carboxylates, the carboxylates are selected from at least one of methyl acetate, ethyl acetate or ethyl propionate, and the content of the first solvent in the electrolyte is 2wt%-15wt%.

6. The lithium-ion battery electrolyte according to claim 5, characterized in that The solvent also includes a second solvent, which includes cyclic esters and chain esters. The cyclic esters are selected from at least one of ethylene carbonate or propylene carbonate, and the content of the cyclic esters in the electrolyte is 8wt%-24wt%. The chain esters are selected from at least one of ethyl methyl carbonate or dimethyl carbonate, and the content of the chain esters in the electrolyte is 40wt%-70wt%.

7. The lithium-ion battery electrolyte according to claim 1, characterized in that The lithium salt includes lithium hexafluorophosphate, and the content of the lithium salt in the electrolyte is 14 wt % to 17 wt %.

8. The lithium-ion battery electrolyte according to claim 1, characterized in that The electrolyte further comprises fluoroethylene carbonate, and the content of the fluoroethylene carbonate in the electrolyte is 2 wt % to 10 wt %.

9. The lithium-ion battery electrolyte according to claim 1, characterized in that The additives further include a second additive, which is selected from at least one of vinylene carbonate, vinyl sulfate, 1,3-propane sultone, lithium difluorooxalatophosphate, or lithium difluorooxalatoborate, and the content of each second additive in the electrolyte is 0.1 wt%-1.5 wt%.

10. A lithium ion battery, characterized in that: include: The positive electrode sheet includes a positive electrode active material, wherein the positive electrode active material has the structural formula of Li x [Ni y Co z Mn t M (1-y-z-t) ]O 2-δ , wherein M is selected from at least one of Cr, Zr, Ca, Mg, Cu, Ti, Al, Mo, W and Zn, 0.9 <x<1.1,0.9≤y<1.0,0≤z<0.1,0≤t<0.1,0≤δ≤0.1; A negative electrode plate, comprising a negative electrode active material, wherein the negative electrode active material is selected from at least one of a graphite-doped silicon-oxygen material and a graphite-doped silicon-carbon material; a separator, disposed between the positive electrode sheet and the negative electrode sheet; and The electrolyte is selected from the lithium ion battery electrolyte according to any one of claims 1 to 9.

11. The lithium-ion battery according to claim 10, characterized in that In the negative electrode active material, the doping content of the silicon-oxygen material or the silicon-carbon material is 1 wt % to 10 wt %.

Images