A cobalt-free lithium-ion battery electrolyte and a cobalt-free lithium-ion battery containing the same.

Abstract

This invention relates to a cobalt-free lithium-ion battery electrolyte and a cobalt-free lithium-ion battery containing the same. The electrolyte comprises a non-aqueous organic solvent, a lithium salt, and additives. The additives include additive A and additive B. Additive A contains a carbon-carbon double bond, and additive B contains sulfur (S). Additive A comprises vinylene carbonate and fluorovinyl carbonate, and additive B comprises methanedisulfonate, ethylene sulfate, and propylene-1,3-sulfonyl lactone. This invention effectively improves upon the problem of simultaneously achieving optimal internal resistance, electrochemical performance, and cycle performance, as well as simultaneously achieving optimal high-temperature and low-temperature cycle performance in cobalt-free lithium-ion batteries.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion batteries, and more particularly to a cobalt-free lithium-ion battery electrolyte and a cobalt-free lithium-ion battery containing the same. Background Technology

[0002] Lithium-ion batteries possess characteristics such as high discharge voltage, high energy density, and low self-discharge, leading to their widespread application in 3C products, electric vehicles, and energy storage. In recent years, with increasingly stringent requirements for energy conservation and environmental protection, the demand for lithium-ion batteries in fields such as power batteries has increased rapidly.

[0003] Currently, most mainstream automakers' vehicles use lithium iron phosphate or ternary nickel-cobalt-manganese lithium batteries as the cathode material. Both have certain issues that need to be addressed: lithium iron phosphate batteries have relatively low energy density and poor low-temperature performance, resulting in a poor user experience in winter; while nickel-cobalt-manganese lithium batteries have high energy density, the scarcity of cobalt leads to higher costs and lower safety performance. Cobalt-free batteries combine the advantages of high energy density and low cost, and have garnered industry attention since their introduction.

[0004] Electrolyte is a key material in batteries. Working in conjunction with the positive and negative electrodes, it plays a crucial role in conducting ions between them, stabilizing the interface, and improving battery lifespan. Currently, commonly used electrolytes include non-aqueous solvents and lithium salts and additives dissolved in non-aqueous solvents. Currently, commonly used additives such as VC (ethylene carbonate) and PS (1,3-propanesulfonate lactone) in power batteries form an SEI film with high impedance. High dosages can easily affect the power battery's power output and low-temperature performance, while also resulting in significant gas generation. Conversely, low dosages fail to form a stable SEI protective film, failing to meet the long cycle life requirements of power batteries.

[0005] Currently, electrolytes used in cobalt-free battery applications commonly employ additives such as VC (ethylene carbonate). These additives form an SEI film with high impedance, and when used in large quantities, they can negatively impact the battery's power output and low-temperature performance, while also leading to significant gas generation. Conversely, when used in small quantities, a stable SEI film cannot be formed, failing to meet the long cycle life requirements of power batteries. Therefore, there is an urgent need to develop power battery electrolytes that can form a low-impedance, structurally stable SEI film on the electrode surface to meet the higher energy density and power density demands of electric vehicle power batteries.

[0006] CN113998745A discloses a cobalt-free cathode material, its preparation method, and its applications. This invention improves the performance of the cobalt-free cathode material by controlling the specific surface area, tap density, median particle size (D50), and their ratio of the precursor and cathode material. The cobalt-free layered cathode material synthesized by the method described in this invention has high capacity and initial efficiency, and its rate performance is improved.

[0007] CN114005978A discloses a cobalt-free cathode material, its preparation method, and its application. The cobalt-free cathode material is obtained by sintering a cobalt-free hydroxide precursor mixed with a lithium source. By controlling the relationship between the full width at half maximum (FWHM) of the characteristic diffraction peaks of the cobalt-free cathode material and the cobalt-free hydroxide precursor, the performance of the cobalt-free cathode material is improved, particularly enhancing its initial efficiency, rate capability, capacity, and cycle life.

[0008] Because the cathode material lacks cobalt, it is more reactive and unstable. Even with doping and coating improvements, the cycle life and gas generation performance of cobalt-free cathode materials still lag behind mature ternary materials. Therefore, it is necessary to consider forming a low-impedance, structurally stable SEI / CEI film on the electrode surface during electrolyte design. This will enable the prepared cobalt-free lithium-ion power battery to have advantages such as long cycle life, high energy density, high output power, and good low-temperature performance. Summary of the Invention

[0009] The purpose of this invention is to provide a cobalt-free lithium-ion secondary battery electrolyte.

[0010] To achieve this objective, the present invention adopts the following technical solution:

[0011] One objective of this invention is to provide a cobalt-free lithium-ion battery electrolyte, the electrolyte comprising a non-aqueous organic solvent, a lithium salt, and additives, wherein the additives comprise additive A and additive B, additive A containing a carbon-carbon double bond, and additive B containing sulfur.

[0012] Additive A includes vinylene carbonate and fluorovinyl carbonate, and additive B includes methanedisulfonate, ethylene sulfate and propylene-1,3-sulfonyl lactone.

[0013] This invention's electrolyte incorporates low-impedance additive A (fluoroethylene carbonate) and additive B (ethylene sulfate and methane disulfonate), while controlling the amount of high-impedance additives such as ethylene carbonate. This allows for the formation of a low-impedance, structurally stable SEI film on the electrode surface. The resulting lithium-ion power battery exhibits advantages such as long cycle life, high energy density, high output power, good low-temperature performance, excellent high-temperature storage performance, and low gas production. Fluoroethylene carbonate is particularly beneficial for forming a dense SEI film, reducing impedance, and improving the electrolyte's low-temperature cycle performance. Ethylene carbonate and fluoroethylene carbonate readily form a stable SEI film on the graphite anode surface, exhibiting excellent high and low temperature performance and anti-gas swelling properties, effectively improving battery capacity and cycle performance.

[0014] Additive B, consisting of methylene methane disulfonate, ethylene sulfate, and propylene-1,3-sulfonyl lactone, all possess the functional groups -SO3 or -SO4. Their decomposition products, such as RSO3Li, exhibit high ionic conductivity and excellent high-temperature performance. Simultaneously, they can form a low-impedance CEI film on the positive electrode surface, inhibiting subsequent electrolyte decomposition. When used in cobalt-free positive electrode batteries, they can suppress the dissolution and adsorption of metal ions on the negative electrode surface, thereby significantly improving the battery's high-temperature cycle performance. Ethyl sulfate is the only single additive comparable to VC, demonstrating superior performance in reducing impedance and improving low-temperature performance. Methylene methane disulfonate has a higher number of -SO3 groups, resulting in a more stable SEI / CEI ratio. During storage and cycling, it lowers battery impedance, suppresses the electrolyte oxidation rate on the positive electrode surface, and reduces self-discharge. The propenyl-1,3-sulfonyl lactone structure contains double bonds, making it more easily reduced. Reduction products include Li₂SO₃ and (CH-CH₂-CH₂-OSO₃Li)₂. The passivation layer composed of these substances has strong polarity, good adhesion to the negative electrode, and is not easily detached. Furthermore, its excellent spatial structure is beneficial for Li… + The transfer process forms a CEI film rich in RSOSR and RSO2SR on the positive electrode side, which improves the high-temperature cycling and storage performance of the battery and reduces gas production.

[0015] This invention relates to a cobalt-free electrolyte applied in cobalt-free batteries. Compared to NCM ternary lithium-ion batteries, cobalt-free batteries lack cobalt, resulting in a more reactive and unstable cathode material. Even with improved cycling and gas generation performance through doping and coating, the cobalt-free cathode material still lags behind mature ternary materials. Single electrolyte additives rarely achieve satisfactory electrochemical performance and always have some drawbacks. Composite additives, utilizing the synergistic effects between various substances, represent a simple and effective method to improve overall battery performance. This invention combines additives A and B, integrating the stable film-forming properties and excellent cycling characteristics of additive A with the low film-forming impedance and cathode protection properties of additive B, significantly enhancing the overall performance of the cobalt-free battery.

[0016] As a preferred embodiment of the present invention, additive A further includes maleic anhydride.

[0017] Preferably, additive B further includes 1,3-propanesulfonyl lactone.

[0018] The maleic anhydride in this invention can easily form a stable SEI film on the graphite anode surface, exhibiting excellent high and low temperature performance and anti-gas expansion performance, which can effectively improve battery capacity and cycle performance. 1,3-propane sulfonyl lactone is used to improve the high temperature performance of the electrolyte.

[0019] As a preferred technical solution of the present invention, with the electrolyte mass being 100%, the vinylene carbonate accounts for 0.2% to 0.7% of the electrolyte mass fraction. The mass fraction can be 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, or 0.7%, etc., but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0020] Preferably, with the electrolyte mass being 100%, the fluoroethylene carbonate accounts for 0.2% to 0.7% of the electrolyte mass fraction. The mass fraction can be 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, or 0.7%, etc., but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0021] Preferably, with the electrolyte mass being 100%, the methylene methane disulfonate accounts for 0.2% to 0.7% of the electrolyte mass fraction. The mass fraction can be 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, or 0.7%, etc., but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0022] Preferably, with the electrolyte mass being 100%, the ethylene sulfate accounts for 0.2% to 0.7% of the electrolyte mass fraction. The mass fraction can be 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, or 0.7%, etc., but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0023] Preferably, with the electrolyte mass being 100%, the propylene-1,3-sulfonyl lactone accounts for 0.2% to 0.7% of the electrolyte mass fraction. The mass fraction can be 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, or 0.7%, etc., but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0024] Preferably, based on the mass of the electrolyte being 100%, the mass fraction of additive A in the electrolyte is 0.4 - 5%, where the mass fraction can be 0.4%, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5% or 4.9%, etc., but is not limited to the listed values. Other unlisted values within this numerical range are equally applicable, and preferably it is 0.4 - 1%.

[0025] Preferably, based on the mass of the electrolyte being 100%, the mass fraction of additive B in the electrolyte is 0.6 - 5%, where the mass fraction can be 0.6%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5% or 4.9%, etc., but is not limited to the listed values. Other unlisted values within this numerical range are equally applicable, and preferably it is m - m + 1, 0 < m < 1, where the value of m can be 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8 or 0.9, etc., but is not limited to the listed values. Other unlisted values within this numerical range are equally applicable.

[0026] In the preferred range of m - m + 1 of additive B in the present invention, the value of m is related to the value of Ni in the positive electrode material in the battery prepared with the cobalt - free electrolyte of the present invention. The value of m is the nickel element content in LiNi m Mn (1-m) O2.

[0027] As a preferred technical solution of the present invention, the non - aqueous organic solvent includes cyclic carbonates and chain - like carbonates.

[0028] Preferably, the cyclic carbonate includes any one or a combination of at least two of ethylene carbonate, propylene carbonate or γ - butyrolactone. Typical but non - restrictive examples of the combination are: the combination of ethylene carbonate and propylene carbonate, the combination of propylene carbonate and γ - butyrolactone, or the combination of ethylene carbonate and γ - butyrolactone, etc.

[0029] Preferably, the chain carbonate comprises any one or a combination of at least two of dimethyl carbonate, diethyl carbonate, butenyl carbonate, diethyl carbonate, dipropyl carbonate, methyl ethyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, methyl formate, ethyl formate, propyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, or propyl propionate. Typical but non-limiting examples of such combinations include: combinations of dimethyl carbonate and butenyl carbonate, combinations of butenyl carbonate and diethyl carbonate, combinations of dipropyl carbonate and methyl ethyl carbonate, combinations of methyl propyl carbonate and ethyl propyl carbonate, combinations of methyl formate and ethyl formate, combinations of propyl formate and methyl acetate, combinations of ethyl acetate and propyl acetate, combinations of methyl propionate and ethyl propionate, or combinations of ethyl propionate and propyl propionate, etc.

[0030] As a preferred embodiment of the present invention, the volume ratio of the cyclic carbonate to the chain carbonate is 1:(1.5 to 2.5), wherein the volume ratio can be 1:1.5, 1:1.8, 1:2, 1:2.1, 1:2.3 or 1:2.5, etc., but is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0031] As a preferred technical solution of the present invention, the lithium salt includes any one or a combination of at least two of LiPF6, LiBF4, LiBOB, LiDFOB, LiAsF6, Li(CF3SO2)2N, Li(FSO2)2N, LiCF3SO3, or LiClO4. Typical but non-limiting examples of the combination include: the combination of LiPF6 and LiBF4, the combination of LiBF4 and LiBOB, the combination of LiAsF6 and Li(CF3SO2)2N, the combination of Li(FSO2)2N and LiCF3SO3, or the combination of LiCF3SO3 and LiClO4, etc.

[0032] Preferably, the concentration of the lithium salt in the electrolyte is 0.5–2.0 mol / L, wherein the concentration may be 0.5 mol / L, 0.6 mol / L, 0.7 mol / L, 0.8 mol / L, 0.9 mol / L, 1.0 mol / L, 1.1 mol / L, 1.2 mol / L, 1.3 mol / L, 1.4 mol / L, 1.5 mol / L, 1.6 mol / L, 1.7 mol / L, 1.8 mol / L, 1.9 mol / L, or 2.0 mol / L, but is not limited to the listed values; other unlisted values ​​within this range are also applicable.

[0033] A second object of the present invention is to provide a cobalt-free lithium-ion battery, which includes the cobalt-free lithium-ion battery electrolyte as described in the first object, and the cobalt-free lithium-ion battery further includes a positive electrode sheet, a negative electrode sheet, and a separator.

[0034] As a preferred technical solution of the present invention, the active material of the positive electrode sheet includes a first active material or a second active material.

[0035] Preferably, the first active material of the positive electrode sheet includes a positive electrode material and a coating layer.

[0036] Preferably, the positive electrode material is LiNi x Mn(1 - x )O2, where 0 < x < 1, and the value of x can be 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, or 0.9, etc., but is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0037] Preferably, the material of the coating layer includes any one or a combination of at least two of ZrO2, Al2O3, MgO, TiO2, Ta2O5, WO3, B2O3, H3BO3, La2O3, SiO2, or Nb2O5. Typical but non-limiting examples of the combination include: the combination of ZrO2 and Al2O3, the combination of Al2O3 and MgO, the combination of TiO2 and Ta2O5, the combination of WO3 and B2O3, the combination of H3BO3 and La2O3, or the combination of SiO2 and Nb2O5, etc.

[0038] Preferably, the second active material of the positive electrode sheet is a positive electrode material containing a doping source.

[0039] Preferably, the positive electrode material is LiNi x Mn (1-x) O2, where 0 < x < 1, and the value of x can be 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, or 0.9, etc., but is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0040] Preferably, the doping source includes any one or a combination of at least two of TiO2, Al2O3, ZrO2, MgO, Ta2O5, WO3, Nb2O5, B2O3, or H3BO3. Typical but non-limiting examples of the combination include: the combination of TiO2 and Al2O3, the combination of ZrO2 and MgO, the combination of MgO and Ta2O5, the combination of WO3 and Nb2O5, or the combination of B2O3 and H3BO3, etc.

[0041] Preferably, the cathode material is LiNi. 0.3 Mn 0.7 O2, LiNi 0.5 Mn 0.5 O2 or LiNi 0.8 Mn 0.2 Any of the following: O2.

[0042] As a preferred technical solution of the present invention, the active material of the negative electrode sheet includes any one or a combination of at least two of natural graphite, artificial graphite, soft carbon, hard carbon, lithium titanate, silicon or silicon-carbon alloy, wherein typical but non-limiting examples of the combination include: a combination of natural graphite and artificial graphite, a combination of soft carbon and hard carbon, a combination of hard carbon and lithium titanate, or a combination of silicon and silicon-carbon alloy, etc.

[0043] As a preferred technical solution of the present invention, the diaphragm includes any one of PE diaphragm, PP / PE / PP diaphragm, ceramic-treated PE diaphragm or PVDF-treated PE diaphragm.

[0044] Compared with the prior art, the present invention has the following beneficial effects:

[0045] This invention effectively improves upon the limitations of simultaneously achieving optimal internal resistance, electrochemical performance, and cycle performance in cobalt-free lithium-ion batteries, as well as simultaneously achieving optimal high-temperature and low-temperature cycle performance. The resulting lithium-ion battery exhibits performance in low-nickel LiNi... 0.3 Mn 0.7 In a system using O2 as the cathode material, the DC internal resistance during discharge at -20℃ can be as low as below 230mΩ, the capacity retention after 500 cycles at 45℃ can be as high as over 85%, the capacity retention after 60 days of storage at 60℃ can be as high as over 80%, and the gas expansion after 60 days of storage at 60℃ can be as low as below 25%; in a medium-nickel LiNi... 0.5 Mn 0.5 In a system using O2 as the cathode material, the DC internal resistance during discharge at -20℃ can be as low as below 240mΩ, the capacity retention after 500 cycles at 45℃ can be as high as over 85%, the capacity retention after 60 days of storage at 60℃ can be as high as over 80%, and the gas expansion after 60 days of storage at 60℃ can be as low as below 25%; in high-nickel LiNi 0.8 Mn 0.2 In a system where O2 is used as the cathode material, the DC internal resistance during discharge at -20℃ can be as low as 240mΩ or less, the capacity retention rate after 500 cycles at 45℃ can be as high as 80% or more, the capacity retention rate after 60 days of storage at 60℃ can be as high as 80% or more, and the gas expansion after 60 days of storage at 60℃ can be as low as 30% or less. Detailed Implementation

[0046] The technical solution of the present invention will be further illustrated below through specific embodiments. Those skilled in the art should understand that the embodiments described are merely illustrative of the present invention and should not be construed as limiting the invention.

[0047] Example 1

[0048] This embodiment provides a cobalt-free lithium-ion battery electrolyte:

[0049] Cobalt-free lithium-ion battery electrolytes include non-aqueous organic solvents, lithium salts, and additives.

[0050] Non-aqueous organic solvents include ethylene carbonate, methyl ethyl carbonate, and diethyl carbonate in a volume ratio of 1:1:1.

[0051] Lithium salts include LiPF6 at a concentration of 1 mol / L in the electrolyte.

[0052] The additives include: based on the mass of the electrolyte, 0.5% by mass of vinylene carbonate, 0.5% by mass of fluorovinyl carbonate, 0.5% by mass of methanedisulfonate, 0.5% by mass of ethylene sulfate, and 0.5% by mass of propylene-1,3-sulfonyl lactone.

[0053] Example 2

[0054] This embodiment provides a cobalt-free lithium-ion battery electrolyte:

[0055] Cobalt-free lithium-ion battery electrolytes include non-aqueous organic solvents, lithium salts, and additives.

[0056] Non-aqueous organic solvents include propylene carbonate and methyl formate in a volume ratio of 1:1.5.

[0057] The lithium salts include LiBF4 at a concentration of 0.5 mol / L in the electrolyte.

[0058] The additives include: based on the mass of the electrolyte, 0.7% vinylene carbonate, 0.2% fluoroethylene carbonate, 0.7% methanedisulfonate, 0.7% ethylene sulfate, and 0.7% propenyl-1,3-sulfonyl lactone, accounting for 100% of the electrolyte mass.

[0059] Example 3

[0060] This embodiment provides a cobalt-free lithium-ion battery electrolyte:

[0061] Cobalt-free lithium-ion battery electrolytes include non-aqueous organic solvents, lithium salts, and additives.

[0062] The non-aqueous organic solvents include γ-butyrolactone and methyl propionate in a volume ratio of 1:2.5.

[0063] Lithium salts include Li(CF3SO2)2N at a concentration of 2 mol / L in the electrolyte.

[0064] The additives include: based on the mass of the electrolyte, 0.2% vinylene carbonate, 0.7% fluoroethylene carbonate, 0.2% methanedisulfonate, 0.2% ethylene sulfate, and 0.2% propenyl-1,3-sulfonyl lactone, accounting for 100% of the electrolyte mass.

[0065] Example 4

[0066] In this embodiment, the conditions are the same as in Example 1, except that 0.5% of methylene disulfonate, 0.5% of ethylene sulfate and 0.5% of propenyl-1,3-sulfonyl lactone in the additives are replaced with 0.1% of methylene disulfonate, 0.1% of ethylene sulfate and 0.1% of propenyl-1,3-sulfonyl lactone.

[0067] Example 5

[0068] In this embodiment, the conditions are the same as in Example 1, except that 0.5% of methylene disulfonate, 0.5% of ethylene sulfate and 0.5% of propenyl-1,3-sulfonyl lactone in the additives are replaced with 1% of methylene disulfonate, 1% of ethylene sulfate and 1% of propenyl-1,3-sulfonyl lactone.

[0069] Example 6

[0070] In this embodiment, the conditions are the same as in Example 1, except that 0.5% of methylene disulfonate, 0.5% of ethylene sulfate and 0.5% of propenyl-1,3-sulfonyl lactone in the additives are replaced with 2% of methylene disulfonate, 2% of ethylene sulfate and 2% of propenyl-1,3-sulfonyl lactone.

[0071] Example 7

[0072] Except for the additives, which include maleic anhydride at a mass fraction of 0.5% and 1,3-propanesulfonyl lactone in the electrolyte, all other conditions in this embodiment are the same as in Example 1.

[0073] Comparative Example 1

[0074] The conditions for this comparative example are the same as those in Example 1, except that vinylene carbonate is not added and the mass fraction of fluoroethylene carbonate in the electrolyte is replaced with 1%.

[0075] Comparative Example 2

[0076] The conditions for this comparative example are the same as those in Example 1, except that fluoroethylene carbonate is not added and the mass fraction of vinylene carbonate in the electrolyte is replaced with 1%.

[0077] Comparative Example 3

[0078] The conditions for this comparative example are the same as those in Example 1, except that methyl methane disulfonate is not added and ethylene sulfate, which accounts for 0.5% of the electrolyte mass fraction, is replaced with 1%.

[0079] Comparative Example 4

[0080] The conditions in this comparative example are the same as in Example 1, except that vinylene sulfate is not added and methyl methane disulfonate, which accounts for 0.5% of the electrolyte mass fraction, is replaced with 1%.

[0081] Comparative Example 5

[0082] The conditions for this comparative example are the same as those for Example 1, except that fluoroethylene carbonate and vinylene carbonate are not added.

[0083] Comparative Example 6

[0084] The conditions for this comparative example were the same as those in Example 1, except that methyl methane disulfonate, ethylene sulfate, and propylene-1,3-sulfonyl lactone were not added.

[0085] Comparative Example 7

[0086] The conditions for this comparative example were the same as those in Example 1, except that fluoroethylene carbonate, vinylene carbonate, ethylene sulfate, propylene-1,3-sulfonyl lactone, and methanedisulfonate were not added.

[0087] The electrolytes from Examples 1-7 and Comparative Examples 1-7 were assembled into batteries, and the battery performance was tested. The test results are shown in Tables 1-3.

[0088] The battery materials and assembly methods are as follows:

[0089] The active material for the positive electrode is low-nickel LiNi. 0.3 Mn 0.7 O2, LiNi (a type of nickel alloy) 0.5 Mn 0.5 O2, high-nickel LiNi 0.8 Mn 0.2 O2; the active material of the negative electrode is natural graphite; the separator is PE membrane.

[0090] Preparation of the positive electrode: using cobalt-free positive electrode active material LiNi x Mn (1-x)O2 (0 < x < 1), conductive agent Super - P, carbon nanotubes CNT, and binder PVDF are dissolved in solvent N - methyl - pyrrolidone in a mass ratio of 96:1:1:2 and mixed evenly to form a positive electrode paste. Then, the positive electrode paste is evenly coated on the current collector aluminum foil, dried, rolled, trimmed, and sliced. After that, it is dried under vacuum at 85°C, and the electrode tab is welded to make a positive electrode sheet of a lithium - ion secondary battery meeting the requirements.

[0091] Preparation of the negative electrode sheet: Artificial graphite as the negative electrode active material, conductive agent Super - P, thickening agent CMC, and binder SBR are dispersed in deionized water in a mass ratio of 97:2:1 and mixed evenly to form a negative electrode paste. Then, the negative electrode paste is evenly coated on the current collector copper foil, dried, rolled, trimmed, and sliced. After that, it is dried under vacuum at 85°C, and the electrode tab is welded to make a negative electrode sheet of a lithium - ion secondary battery meeting the requirements.

[0092] Preparation of the lithium - ion secondary battery

[0093] The positive electrode sheet, negative electrode sheet, and separator membrane (PE membrane) of the lithium - ion secondary battery prepared according to the foregoing process are made into a soft - package battery cell through the stacking process. After removing water, the electrolyte in Examples 1 - 7 and Comparative Examples 1 - 7 is injected, and it is left standing for 24 h. Then, it is charged at a constant current of 0.1C to 4.35V at 45°C, then charged at a constant voltage until the current drops to 0.05C, and then discharged at a constant current of 0.1C to 2.8V. The charge - discharge cycle is repeated twice, and then charged at a constant current of 0.1C to 4.35V (recording the charge capacity), and finally the battery is discharged at a constant current of 0.1C to 2.8V; thus, the preparation of the lithium - ion secondary battery is completed.

[0094] Testing method:

[0095] DC internal resistance test of the lithium - ion secondary battery

[0096] At 25°C, first charge the lithium - ion secondary batteries prepared in Comparative Examples 1 - 7 and Examples 1 - 7 at a constant current of 1C to 4.35V, further charge at a constant voltage of 4.35V until the current is 0.05C, and then discharge the lithium - ion secondary battery at a constant current of 0.5C for 1 hour. At this time, the state of charge of the battery is maintained at 50% SOC. Cool the battery to - 20°C, let it stand for 240 minutes, and record the voltage V1. Then, discharge the battery with a current I (I = 1C) for 10 seconds, and record the discharge - termination voltage V2.

[0097] The calculation formula for the discharge DC internal resistance DCIR of the battery is: DCIR=(V1 - V2) / I (mΩ).

[0098] High - temperature cycle performance test of the lithium - ion secondary battery

[0099] The high-temperature cycling performance of the lithium-ion secondary batteries prepared in Comparative Examples 1-7 and Examples 1-7 was tested. The specific method was as follows: at 45°C, the lithium-ion secondary batteries were first charged to 4.35V with a constant current of 1C, then charged to 0.05C with a constant voltage of 4.35V, and then discharged to 2.8V with a constant current of 1C. This constituted one charge-discharge cycle, and the discharge capacity of this cycle was taken as the discharge capacity of the first cycle. The lithium-ion secondary batteries were subjected to cyclic charge-discharge tests in the above manner, and the discharge capacity of the 500th cycle was recorded. The capacity retention rate (%) of the lithium-ion secondary battery after 500 cycles = [Discharge capacity of the 500th cycle / Discharge capacity of the first cycle] × 100%.

[0100] High-Temperature Storage Performance Test of Lithium-ion Secondary Batteries

[0101] At 25°C, the lithium-ion secondary batteries prepared in Comparative Examples 1-7 and Examples 1-7 were first charged to 4.35V with a constant current of 1C. They were then further charged at a constant voltage of 4.35V until the current reached 0.05C. Finally, the lithium-ion secondary batteries were discharged to 2.8V with a constant current of 1C. This discharge capacity was the discharge capacity of the lithium-ion secondary batteries before high-temperature storage. Next, the lithium-ion secondary batteries were charged to 4.35V with a constant current of 1C and stored at 60°C for 60 days. After storage, the lithium-ion secondary batteries were placed at 25°C and discharged to 2.8V with a constant current of 0.5C. They were then charged to 4.35V with a constant current of 1C, further charged at a constant voltage of 4.35V until the current reached 1C, and finally discharged to 2.8V with a constant current of 1C. This final discharge capacity was the discharge capacity of the lithium-ion secondary batteries after high-temperature storage. Capacity retention rate (%) of lithium-ion secondary battery after high-temperature storage = [Discharge capacity of lithium-ion secondary battery after high-temperature storage / Discharge capacity of lithium-ion secondary battery before high-temperature storage] × 100%.

[0102] High-Temperature Storage Gas Generation Performance Test of Lithium-ion Secondary Batteries

[0103] At 25°C, the lithium-ion secondary batteries prepared in Comparative Examples 1-7 and Examples 1-7 were first charged to 4.35V with a constant current of 1C, and then further charged to a current of 0.05C with a constant voltage of 4.35V. Then, the lithium-ion secondary batteries were discharged to 2.8V with a constant current of 1C. This discharge capacity represents the discharge capacity of the lithium-ion secondary batteries before high-temperature storage. Next, the lithium-ion secondary batteries were charged to 4.35V with a constant current of 1C, and then charged to a current of 0.05C with a constant voltage of 4.35V to fully charge the lithium-ion batteries. The volume of the batteries was tested using the water displacement method, and the thickness was measured using a micrometer. The lithium-ion batteries were then stored at 60°C for 60 days. After storage, the lithium-ion secondary batteries were placed in a 25°C environment, and the volume of the batteries was tested again using the water displacement method, and the thickness was measured using a micrometer. Then, the lithium-ion secondary battery is discharged to 2.8V at a constant current of 0.5C, then charged to 4.35V at a constant current of 1C, and further charged to 1C at a constant voltage of 4.35V. Finally, the lithium-ion secondary battery is discharged to 2.8V at a constant current of 1C. The final discharge capacity is the discharge capacity of the lithium-ion secondary battery after high-temperature storage.

[0104] Battery volume expansion rate = (volume after storage / volume before storage - 1)%.

[0105] The tested positive electrode active material is low-nickel LiNi. 0.3 Mn 0.7 The battery performance under O2 conditions is shown in Table 1.

[0106] Table 1

[0107]

[0108] The tested positive electrode active material was medium-nickel LiNi. 0.5 Mn 0.5 The battery performance under O conditions is shown in Table 2.

[0109] Table 2

[0110]

[0111]

[0112] The tested positive electrode active material is high-nickel LiNi. 0.8 Mn 0.2 The battery performance under O2 conditions is shown in Table 3.

[0113] Table 3

[0114]

[0115]

[0116] As can be seen from Tables 1, 2 and 3, and by comparing Examples 4-6 with Example 1, it can be seen that changing the value range of each component of additive B and additive A results in a deterioration of the electrochemical performance of the battery.

[0117] As can be seen from Examples 1 and 8, adding maleic anhydride to additive A and adding 1,3-propane sulfonyl lactone to additive B does not significantly change the electrochemical performance of the battery, but instead increases the production cost.

[0118] As can be seen from Example 1 and Comparative Examples 1-2, both vinylene carbonate and fluoroethylene carbonate are indispensable; the absence of either one will result in a deterioration of the battery's electrochemical performance.

[0119] As can be seen from Example 1 and Comparative Examples 3-4, methylene disulfonate, ethylene sulfate, and propenyl-1,3-sulfonyl lactone in additive B are indispensable. Without the synergistic effect of methylene disulfonate, ethylene sulfate, and propenyl-1,3-sulfonyl lactone, the electrochemical performance of the battery deteriorates.

[0120] As can be seen from the comparison between Example 1 and Comparative Examples 5-6, only by using additive A and additive B together can excellent battery cycle performance, low battery impedance, and low high-temperature gas generation be achieved.

[0121] A comparison of Example 1 and Comparative Example 7 shows that the electrochemical performance of the battery drops sharply without additives.

[0122] The applicant declares that the above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention fall within the protection and disclosure scope of the present invention.

Claims

1. A cobalt-free lithium-ion battery, characterized by, The cobalt-free lithium ion battery comprises a cobalt-free lithium ion battery electrolyte, a positive electrode sheet, a negative electrode sheet and a separator. The active material of the positive electrode sheet comprises a first active material or a second active material. The first active material of the positive electrode sheet comprises a positive electrode material and a coating layer, and the second active material is a positive electrode material containing a doping source. The positive electrode material is LiNi x Mn (1-x) O2, 0 < x < 1; The electrolyte comprises a non-aqueous organic solvent, a lithium salt and an additive, the additive comprises an additive A and an additive B, the additive A contains a carbon-carbon double bond, and the additive B contains an S element. The additive A comprises 0.2-0.7% of vinylene carbonate and 0.2-0.7% of fluoroethylene carbonate in the electrolyte by mass fraction, and the additive B comprises 0.2-0.7% of methylenemalonate, 0.2-0.7% of ethylene sulfate and 0.2-0.7% of propylene-1,3-sulfonic acid lactone in the electrolyte by mass fraction.

2. The cobalt-free lithium-ion battery of claim 1, wherein, The additive A further comprises maleic anhydride.

3. The cobalt-free lithium-ion battery of claim 1, wherein, The additive B further comprises 1,3-propane sulfolactone.

4. The cobalt-free lithium-ion battery of claim 1, wherein, The additive A accounts for 0.4-5% of the electrolyte by mass fraction.

5. The cobalt-free lithium-ion battery of claim 4, wherein, The additive A accounts for 0.4-1% of the electrolyte by mass fraction.

6. The cobalt-free lithium-ion battery of claim 1, wherein, The additive B accounts for 0.6-5% of the electrolyte by mass fraction.

7. The cobalt-free lithium-ion battery of claim 1, wherein, The additive B accounts for (m-m+1)% of the electrolyte by mass fraction, 0 8. The cobalt-free lithium-ion battery of claim 1, wherein, The non-aqueous organic solvent comprises a cyclic carbonate and a chain carbonate.

9. The cobalt-free lithium-ion battery of claim 8, wherein, The cyclic carbonate comprises any one or a combination of at least two of vinyl carbonate, propylene carbonate or gamma-butyrolactone.

10. The cobalt-free lithium-ion battery of claim 8, wherein, The chain carbonate comprises any one or a combination of at least two of dimethyl carbonate, diethyl carbonate, butylene carbonate, diethyl carbonate, dipropyl carbonate, methyl ethyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, methyl formate, ethyl formate, propyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate or propyl propionate.

11. The cobalt-free lithium-ion battery of claim 8, wherein, The volume ratio of the cyclic carbonate and the chain carbonate is 1:(1.5-2.5).

12. The cobalt-free lithium-ion battery of claim 1, wherein, The lithium salt comprises any one or a combination of at least two of LiPF6, LiBF4, LiBOB, LiDFOB, LiAsF6, Li(CF3SO2)2N, Li(FSO2)2N, LiCF3SO3 or LiClO4.

13. The cobalt-free lithium-ion battery of claim 1, wherein, The concentration of the lithium salt in the electrolyte is 0.5-2.0 mol / L.

14. The cobalt-free lithium-ion battery of claim 1, wherein, The material of the coating layer comprises any one or a combination of at least two of ZrO2, Al2O3, MgO, TiO2, Ta2O5, WO3, B2O3, H3BO3, La2O3, SiO2 or Nb2O5.

15. The cobalt-free lithium-ion battery of claim 1, wherein, The doping source includes any one or a combination of at least two of TiO2, Al2O3, ZrO2, MgO, Ta2O5, WO3, Nb2O5, B2O3 or H3BO3.

16. The cobalt-free lithium-ion battery of claim 1, wherein, The positive electrode material is LiNi 0.3 Mn 0.7 O2, LiNi 0.5 Mn 0.5 O2 or LiNi 0.8 Mn 0.2 O2.

17. The cobalt-free lithium-ion battery of claim 1, wherein, The active material of the negative electrode tab includes any one or a combination of at least two of natural graphite, artificial graphite, soft carbon, hard carbon, lithium titanate, silicon or silicon-carbon alloy.

18. The cobalt-free lithium-ion battery of claim 1, wherein, The separator includes any one of a PE separator, a PP / PE / PP separator, a PE separator treated with ceramics or a PE separator treated with PVDF.

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