Electrolyte and lithium ion battery

Abstract

The present application relates to the technical field of lithium ion battery, especially to an electrolyte and a lithium ion battery. The electrolyte comprises an additive, the structural formula of the additive is shown as formula I, the substituted group comprises any one or more of halogen, mercapto, lithium alcohol and lithium carboxylate, R1, R2 and R3 comprise at least one of the substituted group, and at most one of R1, R2 and R3 is hydrogen atom. The electrolyte of the present application adopts a specific additive, has 2-3 branches in the isocyanuric acid ester structure, and the specific substituted group can promote the generation of cross-linked network structure polymer in the growth process of SEI and CEI, greatly improves the mechanical strength of SEI and CEI, thereby relieving the volume change in the cycle process; and the formed SEI and CEI have uniform texture and strong compatibility, effectively improve the interface impedance, promote the interface conduction of Li + , can effectively improve the cycle performance of the battery and improve the safety of the battery.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery technology, and in particular to an electrolyte and a lithium-ion battery. Background Technology

[0002] In lithium-ion batteries, silicon-based anode particles continuously expose fresh electrode surfaces during volume expansion, leading to repeated growth of the electrolyte interphase (SEI) and continuous consumption of lithium ions in the electrolyte, resulting in battery volume expansion and reduced cycle performance. Secondly, high-nickel ternary materials are highly sensitive to moisture. Lithium salt LiPF6 in the electrolyte readily undergoes hydrolysis, producing harmful components such as HF and PF5, causing damage to the electrode / electrolyte interface (CEI), exacerbating transition metal ion dissolution and surface side reactions. Simultaneously, nickel in high-nickel ternary cathode materials has a strong catalytic effect on the oxidative decomposition of the electrolyte, especially at high voltages. Nickel deposited in the electrode material further intensifies the oxidative decomposition of the electrolyte, exacerbating gas generation and posing safety hazards. By using certain electrolyte additives, high-toughness, high-Li- content can be constructed on the surfaces of both the positive and negative electrodes. + Conductivity and stability of the CEI and SEI interfaces are crucial for the development of power batteries with stable cycle life and high safety and reliability.

[0003] In view of this, the present invention is hereby proposed. Summary of the Invention

[0004] One object of the present invention is to provide an electrolyte that enables the SEI and CEI to form a cross-linked network structure during growth, thereby significantly improving the mechanical strength of the SEI and CEI, mitigating volume changes during cycling, and improving cycling performance.

[0005] Another object of the present invention is to provide a lithium-ion battery containing the above-mentioned electrolyte.

[0006] To achieve the above-mentioned objectives of this invention, the following technical solution is adopted:

[0007] An electrolyte comprising an additive; the additive has the structural formula shown in Formula I.

[0008]

[0009] R1, R2 and R3 are each independently selected from any one of hydrogen atom, substituted or unsubstituted C1-C10 alkyl, substituted or unsubstituted C2-C10 ester alkyl, substituted or unsubstituted C1-C10 trimethoxysilyl and substituted or unsubstituted C1-C10 alkoxy.

[0010] The substituted group includes one or more of halogen, mercapto, lithium alkoxide and lithium carboxylate; R1, R2 and R3 include at least one of the substituted groups; and at most one of R1, R2 and R3 is a hydrogen atom.

[0011] In a specific embodiment of the present invention, R1, R2 and / or R3 have at least one of the following structural formulas:

[0012] (1) x is an integer between 1 and 3, and y is an integer between 1 and 3;

[0013] (2) z is an integer between 2 and 5;

[0014] (3) a is an integer between 2 and 5;

[0015] (4) ＊ -C n H 2n-m F m -F; n is an integer between 2 and 5, and m is 1 or 2.

[0016] In a specific embodiment of the present invention, the additive is selected from any one or more of the following structural formulas:

[0017]

[0018] In a specific embodiment of the present invention, the mass of the additive in the electrolyte is 0.1% to 6% of the total mass of the electrolyte.

[0019] In a specific embodiment of the present invention, the electrolyte further includes lithium salt and organic solvent; the organic solvent includes any one or more of ethylene carbonate (EC), propylene carbonate (PC), butenyl carbonate (BC), fluoroethylene carbonate (FEC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), methyl propyl carbonate (MPC), diphenyl carbonate (DPhC), ethyl acetate (EA), propyl acetate (PA), methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), methyl butyrate (MB), ethyl butyrate (EB), γ-butyrolactone (γ-GBL), acetonitrile (AN), and sulfolane (TMS).

[0020] In a specific embodiment of the present invention, the lithium salt includes lithium hexafluorophosphate (LiPF6) and a second lithium salt; the second lithium salt includes any one or more of lithium tetrafluoroborate (LiBF4), lithium bis(oxalato)borate (LiBOB), lithium difluorooxalato)borate (LiDFOB), lithium difluorodioxalato)phosphate (LiDFOP), lithium bis(fluorosulfonyl)imide (LiFSI), and lithium bis(trifluoromethylsulfonyl)imide (LiTFSI).

[0021] In a specific embodiment of the present invention, the mass of the lithium hexafluorophosphate is 12% to 15% of the total mass of the electrolyte; the mass of the second lithium salt is 0% to 10% of the total mass of the electrolyte.

[0022] The present invention also provides a lithium-ion battery, comprising a positive electrode, a negative electrode, a separator, and an electrolyte as described above.

[0023] In a specific embodiment of the present invention, the positive electrode sheet includes a positive electrode active material, and the chemical formula of the positive electrode active material includes Li. a Ni x Co y Mn z O2, where 0.9≤a≤1.1, 0.6≤x≤0.9, 0<y≤0.2, 0≤z≤0.2, and x+y+z=1.

[0024] In a specific embodiment of the present invention, the negative electrode sheet includes a negative electrode active material, which includes one or more of silicon, silicon-carbon, silicon-oxygen, and silicon metal compounds.

[0025] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0026] (1) The electrolyte of the present invention uses specific additives, which have 2 to 3 branches in the isocyanurate structure. The specific substituents can promote the formation of polymers with cross-linked network structures during the growth of SEI and CEI, greatly improving the mechanical strength of SEI and CEI, thereby alleviating volume changes during cycling (especially silicon anode) and improving cycling performance.

[0027] (2) The lithium-ion battery using the electrolyte of the present invention forms a uniform SEI and CEI with strong compatibility, effectively improving interfacial impedance and promoting Li-ion exchange. + The interface conduction can effectively improve the cycle performance and enhance the safety of high-nickel silicon-based batteries. Detailed Implementation

[0028] The technical solution of the present invention will be clearly and completely described below with reference to specific embodiments. However, those skilled in the art will understand that the embodiments described below are some embodiments of the present invention, but not all embodiments, and are only used to illustrate the present invention, and should not be regarded as limiting the scope of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall be followed. Where the manufacturers of reagents or instruments are not specified, they are all conventional products that can be purchased commercially.

[0029] An electrolyte comprising an additive; the additive has the structural formula shown in Formula I.

[0030]

[0031] R1, R2 and R3 are each independently selected from any one of hydrogen atom, substituted or unsubstituted C1-C10 alkyl, substituted or unsubstituted C2-C10 ester alkyl, substituted or unsubstituted C1-C10 trimethoxysilyl, and substituted or unsubstituted C1-C10 alkoxy.

[0032] The substituted group includes one or more of halogen, mercapto, lithium alkoxide and lithium carboxylate; R1, R2 and R3 include at least one of the substituted groups; and at most one of R1, R2 and R3 is a hydrogen atom.

[0033] Here, alkyl refers to a straight-chain or linear hydrocarbon containing a fully saturated hydrocarbon group; C1-C10 alkyl refers to an alkyl group with 1-10 carbon atoms. The structure of an ester alkyl group can be schematically illustrated as follows: R4 is selected from alkyl groups having 1 to 4 carbon atoms, i.e., C1 to C4 alkyl groups; R5 is selected from alkylene groups having 1 to 5 carbon atoms, i.e., C1 to C5 alkylene groups; C2 to C10 ester alkyl groups refer to ester alkyl groups having 2 to 10 carbon atoms. The structure of a trimethoxysilane can be illustrated as follows: R6 is selected from alkylene groups having 1 to 10 carbon atoms, i.e., C1 to C10 alkylene groups; C1 to C10 trimethoxysilyl groups refer to trimethoxysilyl groups having 1 to 10 carbon atoms. The structure of an alkoxy group can be schematically represented as follows: R7 is selected from alkyl groups with 1 to 10 carbon atoms, i.e., C1 to C10 alkyl groups; C1 to C10 alkoxy groups refer to alkoxy groups with 1 to 10 carbon atoms.

[0034] Substitution or non-substitution can be monosubstituted, polysubstituted, or unsubstituted.

[0035] In the additive of the present invention, at least one of R1, R2, and R3 includes at least one of the defined substituted groups—halogen, mercapto, lithium alkoxide, and lithium carboxylate. That is, one of R1, R2, and R3 (R1, R2, or R3) may include the defined substituted group, two of them (R1 / R2, R1 / R3, R2 / R3) may include the defined substituted group, or all of R1, R2, and R3 may include the defined substituted group. However, when the number of defined substituted groups included in R1, R2, and R3 is ≥2, the types of substituted groups may be the same or different; for example, they may all be halogens, or they may include both halogens and mercapto groups, etc.

[0036] The additive in the electrolyte of this invention contains a branched structure centered on isocyanurate. The resulting SEI and CEI polymer components have a cross-linked network structure, which enhances the mechanical properties of the polymer compared to that formed by short-chain additives and significantly suppresses the volume expansion of the silicon anode. Simultaneously, the thiol groups in the additive exhibit good stability in the sulfur-containing products (Li₂SO₃, Li₂S, and ROSO₂Li, etc.) generated during film formation. + It has strong conductivity and can reduce interface impedance.

[0037] In a specific embodiment of the present invention, the halogen includes any one or more of F, Cl, and Br. Further, the halogen is F.

[0038] In a specific embodiment of the present invention, the alkyl group has 2 to 5 carbon atoms, preferably 2 to 4, that is, the alkyl group is selected from ethyl, propyl, isopropyl, n-butyl, isobutyl, sec-butyl, and tert-butyl; the ester alkyl group has 2 to 7 carbon atoms, preferably 4 to 6, that is, the ester alkyl group can be selected from... The number of carbon atoms of the alkyl and alkylene groups on both sides of the ester group can be adjusted, and they can be branched or straight-chain; the trimethoxysilane group has 4 to 8 carbon atoms, preferably 5 to 7, that is, the trimethoxysilane group is selected from... Wait, the alkylene group attached to the trimethoxysilane can be branched or straight; the alkoxy group has 1 to 5 carbon atoms, preferably 1 to 3, that is, the alkoxy group is selected from methoxy, ethoxy, propoxy, and isopropoxy.

[0039] In a specific embodiment of the present invention, the alkoxy group is a cyclopropyl-substituted alkoxy group. Further, the cyclopropyl substitution position is at the end of the alkoxy group. The specific corresponding structure can be illustrated as follows:

[0040] In a specific embodiment of the present invention, in Formula I, the number of substituted groups is 1 to 8, preferably 2 to 6, and more preferably 2, 3 or 6.

[0041] In different embodiments, the number of substituted groups in Formula I can be 1, 2, 3, 4, 5, 6, 7 or 8.

[0042] The additive structure of this invention has 2-3 branches. Specific substituents promote the formation of a cross-linked network polymer structure during the growth of the SEI and CEI, significantly improving the mechanical strength of the SEI and CEI, thereby mitigating volume changes during cycling (especially in silicon anodes). Simultaneously, lithium-ion batteries using the electrolyte of this invention produce SEI and CEI with uniform texture and strong compatibility, effectively improving interfacial impedance and promoting Li... + The interface conduction is improved, which can effectively improve the cycle performance and safety of the battery as a whole. In addition, the ester and epoxy groups in the additives defined in this invention can form long-chain polymers, increasing the mechanical properties of the passivation layer, thereby further suppressing the strain caused by the volume expansion of the silicon anode and ternary cathode; the presence of F groups can increase the interfacial energy in the formed passivation layer; and the presence of thiol groups can increase the content of sulfur-containing compounds in the passivation layer, further improving the stability of the passivation layer.

[0043] In a specific embodiment of the present invention, R1, R2 and / or R3 have at least one of the following structural formulas:

[0044] (1) x is an integer between 1 and 3, and y is an integer between 1 and 3;

[0045] In different implementations, x can be 1, 2 or 3, and y can be 1, 2 or 3;

[0046] (2) z is an integer between 2 and 5;

[0047] In different implementations, z can be 2, 3, 4 or 5;

[0048] (3) a is an integer between 2 and 5;

[0049] In different implementations, a can be 2, 3, 4 or 5;

[0050] (4) ＊ -C n H 2n-m F m -F; n is an integer between 2 and 5, and m is 1 or 2;

[0051] In different implementations, n can be 2, 3, 4 or 5.

[0052] In a preferred embodiment of the present invention, R1, R2 and / or R3 have at least one of the following structural formulas:

[0053] (1)

[0054] (2)

[0055] (3) a is an integer between 2 and 5;

[0056] In different implementations, a can be 2, 3, 4 or 5;

[0057] (4)

[0058] Here, "*" represents the connection site with N in the isocyanurate backbone structure.

[0059] In a specific embodiment of the present invention, the additive is selected from any one or more of the following structural formulas:

[0060]

[0061] In a specific embodiment of the present invention, the additive is selected from any one or more of the following structural formulas:

[0062]

[0063]

[0064] Among them, additive A1-1 is 1,3,5-tris[2-(3-mercaptopropionyloxy)ethyl]isocyanurate, A2-1 is 1,3,5-tris(ethyl-2-ollithium)isocyanurate, A3-1 is 2,4,6-trioxo-1,3,5-triazine-1,3,5-(1H,4H,6H)-tripropionate lithium, A4-1 is 1,3,5-tris(2,3-difluoropropyl)isocyanurate, and A5-1 is dihydro-2,4,6-trioxo-1,3,5-triazine-1,3(2H,4H)-dipropionate lithium.

[0065] In a specific embodiment of the present invention, the mass of the additive in the electrolyte is 0.1% to 6% of the total mass of the electrolyte, such as 0.1% to 1%.

[0066] In different embodiments, the mass of the additive in the electrolyte can be a range of 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.8%, 1%, 2%, 3%, 4%, 5%, 6% or any combination thereof of the total mass of the electrolyte.

[0067] If the additive content in the electrolyte is insufficient, a robust interfacial passivation layer may not be formed, affecting the effectiveness; conversely, if the additive content is too high, the passivation layer may become too thick, leading to Li... + Excessive diffusion resistance increases polarization.

[0068] In a specific embodiment of the present invention, the electrolyte further includes lithium salt and organic solvent; the organic solvent includes any one or more of ethylene carbonate (EC), propylene carbonate (PC), butenyl carbonate (BC), fluoroethylene carbonate (FEC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), methyl propyl carbonate (MPC), diphenyl carbonate (DPhC), ethyl acetate (EA), propyl acetate (PA), methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), methyl butyrate (MB), ethyl butyrate (EB), γ-butyrolactone (γ-GBL), acetonitrile (AN), and sulfolane (TMS).

[0069] In a specific embodiment of the present invention, the organic solvent includes ethylene carbonate (EC) and diethyl carbonate (DEC). Further, the volume ratio of ethylene carbonate (EC) to diethyl carbonate (DEC) is (2.5-3.5):(6.5-7.5), such as 3:7.

[0070] In a specific embodiment of the present invention, the lithium salt includes lithium hexafluorophosphate (LiPF6) and a second lithium salt; the second lithium salt includes any one or more of lithium tetrafluoroborate (LiBF4), lithium bis(oxalato)borate (LiBOB), lithium difluorooxalato)borate (LiDFOB), lithium difluorodioxalato)phosphate (LiDFOP), lithium bis(fluorosulfonyl)imide (LiFSI), and lithium bis(trifluoromethylsulfonyl)imide (LiTFSI).

[0071] Lithium hexafluorophosphate exhibits moderate ion transference number, moderate dissociation constant, good antioxidant properties, and good aluminum foil passivation ability in commonly used organic solvents, and can be matched with various positive and negative electrode materials.

[0072] In a specific embodiment of the present invention, the mass of the lithium hexafluorophosphate is 12% to 15% of the total mass of the electrolyte; the mass of the second lithium salt is 0% to 10% of the total mass of the electrolyte, such as 0.5% to 2%.

[0073] Too low a concentration of lithium hexafluorophosphate affects the conductivity of the electrolyte, while too high a concentration increases the viscosity, also affecting conductivity. The second lithium salt, acting as an auxiliary lithium salt, improves electrolyte stability and lithium-ion transference number; its concentration should not be too high, otherwise it will negatively impact electrolyte conductivity.

[0074] In different embodiments, the mass of the lithium hexafluorophosphate may be a range of 12%, 12.2%, 12.5%, 12.8%, 13%, 13.2%, 13.5%, 13.8%, 14%, 14.2%, 14.5%, 14.8%, 15% or any combination thereof of the total mass of the electrolyte.

[0075] The present invention also provides a method for preparing any one of the above-described electrolytes, comprising the following steps:

[0076] Under a protective atmosphere, a mixture of lithium salt and organic solvent is mixed with additives to obtain an electrolyte.

[0077] The preparation of the mixture of lithium salt and organic solvent includes: adding lithium salt to organic solvent one by one under a protective atmosphere, continuously stirring and controlling the internal temperature rise to not exceed 2°C, and mixing evenly to obtain a mixture of lithium salt and organic solvent.

[0078] The present invention also provides a lithium-ion battery, comprising a positive electrode, a negative electrode, a separator, and any one of the electrolytes described above.

[0079] In a specific embodiment of the present invention, the positive electrode sheet includes a positive electrode active material, the chemical formula of which includes Li. a Ni x Co y Mn z O2, where 0.9≤a≤1.1, 0.6≤x≤0.9, 0<y≤0.2, 0≤z≤0.2, and x+y+z=1.

[0080] In a specific embodiment of the present invention, the negative electrode sheet includes a negative electrode active material, which includes one or more of silicon, silicon-carbon, silicon-oxygen, and silicon metal compounds.

[0081] Examples 1-9

[0082] The present invention provides an electrolyte and a lithium-ion battery containing the corresponding electrolyte.

[0083] The lithium-ion battery provided in this embodiment includes a positive electrode, a negative electrode, a separator, and an electrolyte. The preparation method of the lithium-ion battery may include the following steps:

[0084] (1) Preparation of the positive electrode: The positive electrode active material Li(Ni) is prepared. 0.9 Mn 0.05 Co 0.05O2 (NMC90), conductive agent acetylene black (Super P), and binder polyvinylidene fluoride (PVDF) are mixed evenly in a mass ratio of NMC90:Super P:PVDF = 94:3:3, and then uniformly dispersed in 1-methyl-2-pyrrolidone (NMP) to form a uniform black paste. The mixed black paste is coated on both sides of aluminum foil, and after baking, rolling, and cutting, the positive electrode sheet is obtained.

[0085] (2) Preparation of negative electrode sheet: The negative electrode active material components silicon suboxide (SiO), artificial graphite, conductive agent acetylene black (Super P) and binder SBR are mixed evenly in the mass ratio of silicon suboxide: artificial graphite: Super P: SBR = 11:83:3:3, and then evenly dispersed in deionized water to form a uniform black slurry. The mixed black slurry is coated on both sides of copper foil, and then baked, rolled, and cut into sheets to obtain the negative electrode sheet.

[0086] (3) Fabrication of soft-pack battery: The prepared positive electrode, separator and negative electrode are stacked in sequence, with the separator in the middle of the positive and negative electrode. After winding, hot pressing and shaping, the tabs are welded to obtain the bare cell. The bare cell is placed in the outer packaging aluminum-plastic film and baked in an oven at 85±10℃ for 24 hours. The electrolyte is injected into the dried battery, and the battery is allowed to stand, form and be divided to complete the preparation of lithium-ion soft-pack battery.

[0087] The electrolytes used in the lithium-ion batteries of Examples 1-9 are mainly prepared from lithium salts, organic solvents, and additives. Specifically, the preparation methods of each electrolyte may include the following steps:

[0088] (a) At room temperature, in a glove box filled with argon (H2O < 1 ppm, O2 < 1 ppm), the organic solvents were mixed uniformly in proportion to obtain a mixed solvent, and then... Molecular sieves are used for water removal and are ready for use.

[0089] (b) At room temperature, lithium salts were added sequentially to the mixed solvent obtained in step (a) in a glove box filled with argon gas, while stirring continuously and using dry ice to control the temperature rise to no more than 2°C, to obtain a colorless and transparent liquid.

[0090] (c) At room temperature, in a glove box filled with argon, add the additive to the colorless and transparent liquid obtained in step (b) to obtain the electrolyte.

[0091] The types and amounts of raw materials used in the electrolytes of the lithium-ion batteries in Examples 1 to 9 are shown in Table 1.

[0092] Table 1. Composition information of electrolytes in different embodiments

[0093]

[0094]

[0095] Note: The amounts of lithium salt and additives refer to their respective mass percentages in the final electrolyte; the volume ratio of organic solvents in wastewater refers to the volume ratio among various solvents.

[0096] Comparative Example 1

[0097] Comparative Example 1 refers to the lithium-ion battery and preparation method of Example 1, except that the electrolyte is different. No additives were added to the electrolyte of Comparative Example 1.

[0098] Comparative Example 2

[0099] Comparative Example 2 uses the same lithium-ion battery and preparation method as Example 1, except that the electrolyte is different. In Comparative Example 2, A1-1 in the electrolyte of Example 1 is replaced with an equal mass of the following compound B1:

[0100]

[0101] Comparative Example 3

[0102] Comparative Example 3 refers to the lithium-ion battery and preparation method of Example 1, except that the electrolyte is different. In Comparative Example 3, A1-1 in the electrolyte of Example 1 is replaced with an equal mass of the following compound B2:

[0103]

[0104] Experimental Example 1

[0105] To compare and illustrate the properties of the electrolytes in different embodiments and comparative examples, the performance of lithium-ion batteries in different embodiments and comparative examples was tested, and the test results are shown in Table 2.

[0106] The test items include:

[0107] (1) Room temperature DCR test: At 25±2℃, the soft-pack batteries obtained in Examples 1-9 and Comparative Examples 1-3 were charged to 4.2V at 1C, then discharged at 1C capacity for 30 minutes. After adjusting to 50% SOC, they were pulsed discharged at 5C for 10 seconds and then charged for 10 seconds. The DCR was calculated as (voltage before pulse discharge - voltage after pulse discharge) / discharge current × 100%. After storage at 60℃ for 30 days, the DCR was tested again when the battery was completely cooled to 25±2℃. The internal resistance change rate was calculated as (DCR after 30 days - DCR before 30 days) / DCR before 30 days × 100%.

[0108] (2) Room temperature cycle performance test: At 25±2℃, the pouch batteries obtained in Examples 1-9 and Comparative Examples 1-3 were subjected to charge-discharge cycle tests at a charge-discharge rate of 1C / 1C within a range of 2.8-4.2V, and the discharge specific capacity of the battery in the first cycle and the discharge specific capacity after 1000 cycles were recorded. Capacity retention rate after 500 cycles = discharge specific capacity after 500 cycles / discharge specific capacity in the first cycle × 100%.

[0109] (3) High-temperature storage performance: The pouch batteries obtained in Examples 1-9 and Comparative Examples 1-3 were placed at 60±2℃ and subjected to charge-discharge tests at a charge-discharge rate of 1C / 1C within the range of 2.8-4.2V. The discharge specific capacity of the batteries in the first week was recorded. After that, the batteries were stored at 60±2℃ for 30 days, and the charge-discharge test was performed again, and the discharge specific capacity was recorded. High-temperature storage capacity retention rate = discharge specific capacity after 7 days / discharge specific capacity in the first week × 100%.

[0110] (4) High-temperature gas generation test: The pouch batteries obtained in Examples 1-9 and Comparative Examples 1-3 were charged at a constant current rate of 1C to 4.2V at 25±2℃, and then charged at a constant voltage of 4.2V until the current was below 0.05C, so that they were in a fully charged state at 4.2V. The volume of the fully charged battery before storage was measured and recorded as V0; then the fully charged battery was placed in an oven at 70±2℃. After two days, the battery was taken out and its volume after storage was immediately measured and recorded as V1. Volume expansion rate = (V1-V0) / V0×100%.

[0111] Table 2. Composition information of electrolytes in different embodiments.

[0112]

[0113]

[0114] Analysis of experimental results:

[0115] (1) Comparing the data from Examples 1-3 and the comparative examples, it can be seen that the addition of additive A1-1 can effectively reduce the DCR of the battery and the impact of high-temperature storage on the DCR, while improving the cell's room-temperature cycling performance and high-temperature storage gas generation performance. Simultaneously, additive A1-1 also has a significant inhibitory effect on storage gas generation in the cell. Comparing the electrolyte systems with different contents of additive A1-1 in Table 2, the electrolyte with 0.2 wt% A1-1 showed the best electrochemical performance and storage gas generation performance.

[0116] (2) Comparing the experimental data of Examples 4-6 and the comparative examples, it can be seen that the addition of additive A2-1 can effectively reduce the DCR of the battery and the impact of high-temperature storage on the DCR, while improving the cell's room-temperature cycling performance and high-temperature storage gas generation performance. Simultaneously, additive A2-1 also has a significant inhibitory effect on storage gas generation in the cell. Comparing the electrolyte systems with different contents of A2-1 additive in Table 2, the electrolyte with 0.5 wt% A2-1 showed the best electrochemical performance and storage gas generation performance. In particular, because A2-1 has the smallest molecular weight, its solubility in the electrolyte is the highest among the various additives.

[0117] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions 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. A lithium-ion battery, characterized by, The battery includes a positive electrode sheet, a negative electrode sheet, a separator, and an electrolyte; the electrolyte includes an additive; the additive has a structural formula as shown in Formula I; ； R1, R2, and R3 are each independently selected from a hydrogen atom and at least one of the following structural formulas: (1) x is an integer between 1 and 3, and y is an integer between 1 and 3; (2) ; z is an integer between 2 and 5; and at most one of R1, R2, and R3 is a hydrogen atom; The positive electrode sheet includes a positive electrode active material, a chemical formula of the positive electrode active material includes Li a Ni x Co y Mn z O2, wherein 0.9≤a≤1.1, 0.6≤x≤0.9, 0 The negative electrode sheet includes a negative electrode active material, and the negative electrode active material includes any one or more of silicon, silicon-carbon, silicon-oxygen, and silicon-metal compounds.

2. The lithium-ion battery of claim 1, wherein, The additive is selected from any one or more of the following structural formulas: 、 。 3. The lithium-ion battery of claim 1, wherein, In the electrolyte, the mass of the additive is 0.1% to 6% of the total mass of the electrolyte.

4. The lithium-ion battery of claim 1, wherein, Further including a lithium salt and an organic solvent; The organic solvent includes any one or more of ethylene carbonate, propylene carbonate, butylene carbonate, fluoroethylene carbonate, dimethyl carbonate, methyl ethyl carbonate, diethyl carbonate, methyl propyl carbonate, diphenyl carbonate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, gamma-butyrolactone, acetonitrile, and sulfolane.

5. The lithium-ion battery of claim 4, wherein, The lithium salt includes lithium hexafluorophosphate and a second lithium salt; the second lithium salt includes any one or more of lithium tetrafluoroborate, lithium bis(oxalato)borate, lithium difluoro(oxalato)borate, lithium difluoro-bis(oxalato)phosphate, lithium bis(fluorosulfonyl)imide, and lithium bis(trifluoromethylsulfonyl)imide.

6. The lithium-ion battery of claim 5, wherein, The mass of the lithium hexafluorophosphate is 12% to 15% of the total mass of the electrolyte; and the mass of the second lithium salt is 0% to 10% of the total mass of the electrolyte.

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