Electrolyte additive composition, electrolyte, and battery

Abstract

The application provides an electrolyte additive composition, an electrolyte and a battery, and relates to the technical field of lithium ion batteries. The electrolyte additive composition comprises a lithium salt additive and an electrolyte functional additive, and the structural formula of the electrolyte functional additive is: the electrolyte functional additive with the specific structural formula is applied to the battery as the electrolyte additive, so that the problem that the capacity seriously attenuates in the cycle process of the battery under high voltage can be effectively improved, and the cycle life of the battery is prolonged.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of lithium ion batteries, in particular to an electrolyte additive composition, an electrolyte and a battery. BACKGROUND

[0002] With the development of portable electronic devices and electric vehicles, consumers' requirements for endurance are increasing. The energy density of the battery directly determines the length of time for a single use, and high energy density can provide longer use time. At present, the energy density is mainly improved by increasing the working voltage of the lithium ion battery. However, as the working voltage continues to increase, the electrode potential of the positive electrode material also increases, which will bring a series of negative effects, mainly manifested in: under high voltage, the solvent molecules and lithium salt components in the electrolyte are more likely to oxidize and decompose on the surface of the positive electrode, generating harmful substances such as water and HF. These substances not only consume active lithium, but also react with the positive electrode material, causing the structure of the positive electrode material to be damaged and the transition metal to be dissolved out. After the transition metal is dissolved out, it may be reduced on the surface of the negative electrode, damaging the solid electrolyte interface film (i.e. SEI film) on the surface of the negative electrode, further exacerbating the increase in the internal resistance of the battery, resulting in serious capacity attenuation of the battery during the cycle process. SUMMARY

[0003] The main purpose of the present application is to provide an electrolyte additive composition, an electrolyte and a battery to solve the problem of capacity attenuation of the battery during the cycle process under high voltage in the related art.

[0004] In order to achieve the above-mentioned purpose, according to the first aspect of the present application, an electrolyte additive composition is provided, the electrolyte additive composition comprising a lithium salt additive and an electrolyte functional additive, the structural formula of the electrolyte functional additive being as shown in Formula 1:

[0005]

[0006] Further, the mass ratio of the lithium salt additive to the electrolyte functional additive is (0.5-1):(0.3-1).

[0007] Further, the electrolyte additive composition further comprises a carbonate additive; the mass ratio of the carbonate additive to the electrolyte functional additive is (0.1-1):(0.3-1).

[0008] Further, the carbonate additive comprises at least one of vinylene carbonate and fluoroethylene carbonate.

[0009] Further, the lithium salt additive comprises at least one of lithium bisfluorosulfonylimide, lithium difluorophosphate, lithium borate, lithium bisfluoroborate and lithium hexafluorophosphate.

[0010] Further, the electrolyte additive composition further comprises a sulfur-containing additive; a mass ratio of the sulfur-containing additive to the electrolyte functional additive is (0.5-3):(0.3-1).

[0011] Further, the sulfur-containing additive comprises at least one of propylene sulfite, 1,3-propane sultone, and ethylene sulfate.

[0012] According to a third aspect of the present application, an electrolyte is provided, the electrolyte comprising a lithium salt, an organic solvent, and the electrolyte additive composition provided by the second aspect.

[0013] Further, a mass fraction of the lithium salt in the electrolyte is 10%-15%; and / or,

[0014] a mass fraction of the organic solvent in the electrolyte is 80%-90%; and / or,

[0015] a mass fraction of the electrolyte additive composition in the electrolyte is greater than 0 and less than or equal to 5%.

[0016] Further, a mass fraction of the electrolyte functional additive in the electrolyte is 0.3%-1%; and / or,

[0017] a mass fraction of the lithium salt additive in the electrolyte is 0.5%-1%; and / or,

[0018] a mass fraction of the carbonate additive in the electrolyte is 0.1-1%; and / or,

[0019] a mass fraction of the sulfur-containing additive in the electrolyte is 0.5%-3%.

[0020] Further, the organic solvent comprises at least one of a cyclic carbonate, a chain carbonate, and a chain carboxylic acid ester.

[0021] Further, the organic solvent comprises a cyclic carbonate, a chain carbonate, and a chain carboxylic acid ester, wherein a mass ratio of the cyclic carbonate, the chain carbonate, and the chain carboxylic acid ester is (1-15):(20-70):(5-20).

[0022] According to a fourth aspect of the present application, a battery is provided, the battery comprising the electrolyte provided by the third aspect.

[0023] Further, the battery further comprises a negative electrode sheet containing a negative electrode active material; and / or,

[0024] the battery further comprises a positive electrode sheet containing a positive electrode active material.

[0025] Preferably, the negative electrode active material comprises a carbon-based negative electrode material; and the positive electrode active material comprises Li2MnO3, LiMn 0.375 Ni 0.375 Co0.25 At least one of O2;

[0026] More preferably, the positive electrode active material is Li2MnO3, LiMn 0.375 Ni 0.375 Co 0.25 O2 mixture, including Li2MnO3, LiMn 0.375 Ni 0.375 Co 0.25 The mass ratio of O2 is (0~25):(75~100).

[0027] By applying the technical solution of the present application, an electrolyte functional additive with a specific structural formula is applied to a battery as an electrolyte additive. First, the C=C bond in the molecular structure of the electrolyte functional additive can cause it to preferentially undergo oxidation and reduction reactions on the surfaces of the positive and negative electrodes, participating in the formation of more stable CEI and SEI films with better lithium conductivity, effectively reducing the contact between the electrolyte and the positive and negative electrodes, reducing the occurrence of side reactions, and maintaining good lithium ion transmission performance; secondly, the carbon-nitrogen bond in the molecular structure of the electrolyte functional additive can eliminate harmful substances such as water and HF, effectively reducing the concentration of these harmful substances, and improving the stability of the electrolyte; in addition, the pyridine N in the molecular structure of the electrolyte functional additive can form a coordination bond with the transition metal, reducing the damage of the transition metal ions in the electrolyte to the SEI film, thereby effectively improving the problem of severe capacity decay during the battery cycle at high voltage and extending the cycle life of the battery. DETAILED DESCRIPTION

[0028] As described in the background of this application, batteries in the prior art have the problem of capacity decay during cycling at high voltages. To address the above problem, the first aspect of this application provides an electrolyte additive composition comprising a lithium salt additive and the electrolyte functional additive provided in the first aspect. The structural formula of the electrolyte functional additive is shown in Formula 1:

[0029]

[0030] The C=C bonds in electrolyte functional additives preferentially induce redox reactions at the electrodes, contributing to the formation of more stable CEI and SEI membranes with improved lithium conductivity. Optimizing CEI and SEI membranes is key to improving battery performance. They reduce contact between the electrolyte and electrode materials, minimizing side reactions while maintaining good lithium ion transport, thereby enhancing battery cycle stability.

[0031] The carbon-nitrogen bond in the electrolyte functional additive can react with water and HF in the electrolyte, effectively reducing the concentration of these harmful substances. Water and HF are prone to side reactions with positive electrode materials under high voltage conditions, leading to unstable interfaces and decreased electrochemical performance. The presence of the electrolyte functional additive can significantly reduce such side reactions, improve the stability of the electrolyte, and thus prolong the cycle life of the battery and maintain its high capacity.

[0032] The pyridine N atom in the electrolyte functional additive can form a coordination bond with transition metal ions, which helps to passivate transition metal ions released from the positive electrode material. During the charge and discharge cycle, transition metal ions may be dissolved from the positive electrode material, damaging the SEI film on the negative electrode surface and leading to a decrease in battery performance. The electrolyte functional additive can reduce the damage of transition metal ions to the SEI film, protect the negative electrode material, and further improve the cycle stability and safety of the battery.

[0033] In summary, the entire molecular structure of the electrolyte functional additive produces multiple synergies in the electrolyte, improving the chemical properties of the electrolyte and the physical and chemical properties of the electrode surface, optimizing the formation of CEI and SEI films, eliminating water and HF in the electrolyte, and passivating transition metal ions. This effectively improves the severe capacity decay problem during battery cycling, especially preventing rapid capacity decay during high-voltage cycling, and prolongs the cycle life of the battery.

[0034] In addition, by introducing the electrolyte functional additive, the formation of CEI and SEI films with better lithium conductivity is promoted, and the voltage drop during battery cycling is reduced, thereby improving the overall cycle performance of the battery. In addition, by reducing the side reactions of the electrolyte and electrode materials, especially inhibiting the generation of harmful gases, the risk of internal pressure and thermal runaway in the battery is reduced, thereby improving the safety of the battery.

[0035] In some embodiments, the mass ratio of the lithium salt additive to the electrolyte functional additive is (0.5-1):(0.3-1).

[0036] The lithium salt additive has high oxidative stability and can participate in electrochemical reactions, maintaining the stability of the electrolyte under high voltage and reducing electrolyte decomposition. At the same time, the chemical bonds in the electrolyte functional additive can eliminate H2O and HF in the electrolyte. Therefore, under the synergistic effect of the lithium salt additive and the electrolyte functional additive, the stability of the electrolyte under high voltage conditions can be significantly improved.

[0037] The electrolyte functional additive forms a uniform and dense CEI film on the positive electrode surface, reducing the side reactions of the electrolyte on the positive electrode surface and the dissolution of transition metals; at the same time, the lithium salt additive can participate in the formation of the SEI film and the CEI film, and under the joint action of the electrolyte functional additive and the lithium salt additive, the stability and density of the film can be promoted, thereby reducing the interface impedance and reducing the side reactions, and the discharge capacity and average voltage of the battery can be maintained, thereby improving the cycle life of the battery.

[0038] In addition to the improvement of the cycle life, by introducing the lithium salt additive, the performance of the battery at high and low temperatures can be improved, and the generation of harmful gases (such as H2, CO, CO2, etc.) in the battery can be reduced, thereby reducing the risk of internal pressure and thermal runaway of the battery, and improving the safety performance of the battery.

[0039] In summary, through the mutual cooperation of the lithium salt additive and the electrolyte functional additive, the stability of the electrolyte is improved, the formation of the SEI film / CEI film is optimized, the cycle life of the battery is prolonged, the performance of the battery at high and low temperatures is improved, and the safety of the battery is improved, so that the battery can maintain more stable performance and longer service life when facing high voltage, meeting the high requirements of modern electronic equipment and new energy vehicles on battery performance.

[0040] The mass ratio of the lithium salt additive to the electrolyte functional additive is (0.5-1):(0.3-1), for example, it can be 0.5:1, 1:1, 1:0.5, 1:0.3, or a range composed of any two of them. By limiting the mass ratio of the lithium salt additive to the electrolyte functional additive, the chemical properties of the electrolyte and the physical structure of the protective film can be optimized to ensure the conductivity, chemical stability and electrochemical window of the electrolyte, improve the performance of the battery at different temperatures, and be particularly suitable for use in environments with large temperature fluctuations, such as outdoor energy storage equipment.

[0041] The present application does not limit the specific type of lithium salt additive, which can be a conventional lithium salt additive in the art. For example, in some preferred embodiments, the lithium salt additive includes at least one of lithium bisfluorosulfonylimide (LiFSI), lithium difluorophosphate (LiPO2F2), lithium borate, lithium borate difluoride, and lithium hexafluorophosphate.

[0042] In some embodiments, the electrolyte additive composition further includes a carbonate additive; the mass ratio of the carbonate additive to the electrolyte functional additive is (0.1-1):(0.3-1).

[0043] The carbonate additive can form an SEI film on the negative electrode surface, and the formation of the SEI film can reduce the formation of lithium dendrites and the direct oxidation of the negative electrode material, thereby reducing the risk of short circuit of the battery and further improving the cycle life and safety of the battery.

[0044] Carbonate-based additives have a high oxidation potential, good chemical stability and thermal stability. By adding carbonate-based additives, the conductivity of the electrolyte can be improved, further widening the electrochemical window of the electrolyte, allowing the electrolyte to remain stable in a wider voltage range, which helps the battery to maintain performance when operating at high voltage. Secondly, the addition of carbonate-based solvents can optimize the volatility of the electrolyte, reduce the evaporation of the electrolyte during high temperature or charging and discharging, and enhance the thermal stability of the battery, especially for devices that require high power output, improving the overall safety of the battery. In addition, carbonate-based additives have a low freezing point, which can improve the flowability and conductivity of the electrolyte under low temperature conditions, thereby improving the performance and reliability of the battery in low temperature environments.

[0045] In summary, by introducing carbonate-based additives, under the combined action of lithium salt additives, electrolyte functional additives and carbonate-based additives, the composition of the electrolyte is optimized, which can not only further improve the cycle stability and voltage drop of the battery at high voltage, but also significantly improve the safety, low temperature performance, etc. of the battery.

[0046] The mass ratio of carbonate-based additives to electrolyte functional additives is (0.1-1):(0.3-1), for example 0.1:1, 0.8:1, 1:1, 1:0.8, 1:0.5, 1:0.3 or a range consisting of any two of them. By limiting the ratio of carbonate-based additives to electrolyte functional additives, the physical and chemical properties of the entire electrolyte, including viscosity, conductivity and chemical stability, etc. can be optimized, thereby improving the overall performance of the battery.

[0047] The present application does not limit the specific type of carbonate-based additives, which can be conventional carbonate-based additives in the art. For example, in some embodiments, the carbonate-based additive includes at least one of vinylene carbonate (VC), fluoroethylene carbonate.

[0048] In some embodiments, the electrolyte additive composition further includes a sulfur-containing additive; the mass ratio of the sulfur-containing additive to the electrolyte functional additive is (0.5-3):(0.3-1).

[0049] The sulfur-containing additive can promote the formation of SEI film and CEI film, optimize the physical properties of SEI / CEI film, and further reduce the interface impedance of the battery. The sulfur-containing additive has good thermal stability and electrochemical stability, which not only improves the stability and hydrolysis resistance of the electrolyte at high voltage, but also maintains the integrity of the SEI / CEI film at a higher temperature, reduces the negative impact of high-temperature charge-discharge cycling on the performance of the battery, and enables the battery to maintain good performance in a high-temperature environment. The sulfur-containing additive generally has good solvent compatibility and electrical conductivity, which can improve the overall conductivity of the electrolyte and optimize the charge-discharge efficiency of the battery.

[0050] In summary, the addition of the sulfur-containing additive not only further reduces the capacity decay and voltage drop of the battery during cycling, but also enhances the stability of the electrolyte and the high-temperature performance of the battery, optimizes the electrical conductivity, enhances the interface stability of the battery, and further improves the overall performance of the battery.

[0051] The mass ratio of the sulfur-containing additive to the electrolyte functional additive is (0.5-3):(0.3-1), for example, it can be 0.5:1, 0.8:1, 1:1, 2:1, 3:1, 3:0.5, 3:0.3, or a range composed of any two of them. By limiting the mass ratio of the sulfur-containing additive to the electrolyte functional additive within the above range, the SEI / CEI film formation inside the battery can be optimized through synergistic effect, which not only further reduces the capacity decay and voltage drop of the battery during cycling, but also improves the thermal stability and low-temperature performance of the battery.

[0052] The present application does not limit the specific type of sulfur-containing additive, which can be a conventional sulfur-containing additive in the art. For example, in some embodiments, the sulfur-containing additive includes at least one of propylene sulfite (PS), 1,3-propane sultone (PST), and diethyl sulfite (DTD).

[0053] In a third aspect, the present application provides an electrolyte, which includes a lithium salt, an organic solvent, and the electrolyte additive composition provided in the second aspect.

[0054] Due to the inclusion of the above-mentioned electrolyte additive composition, the electrolyte can form a more stable electrochemical environment inside the battery, effectively improve the problems of severe capacity decay and voltage drop during high-voltage cycling of the battery, and prolong the cycle life of the battery. The electrolyte is suitable for lithium-ion batteries.

[0055] The lithium salt is the main source of conductive ions in the electrolyte. In some embodiments, the mass fraction of the lithium salt in the electrolyte is 10% to 15%. By limiting the addition amount of the lithium salt in the above range, it can be ensured that the electrolyte has sufficient electrical conductivity to ensure efficient ion transmission of the battery during charging and discharging, and at the same time, there is enough lithium salt to participate in the formation of the SEI / CEI film.

[0056] The mass fraction of the lithium salt in the electrolyte is 10% to 15%, for example, 10%, 11%, 12%, 13%, 14%, 15%, or a range formed by any two of them.

[0057] In some embodiments, the mass fraction of the electrolyte additive composition in the electrolyte is greater than 0 and less than or equal to 5%. By limiting the addition amount of the electrolyte additive composition in the above range, it can be ensured that the electrolyte additive composition can maximize its effective function in the electrolyte.

[0058] The mass fraction of the electrolyte additive composition in the electrolyte is greater than 0 and less than or equal to 5%, for example, 0.1%, 0.5%, 1%, 2%, 3%, 4%, 5%, or a range formed by any two of them.

[0059] The organic solvent is the main component of the electrolyte, responsible for transporting lithium ions. In some embodiments, the mass fraction of the organic solvent in the electrolyte is 80% to 90%. By limiting the addition amount of the organic solvent in the above range, sufficient fluidity can be provided to ensure fast transmission of lithium ions between electrodes, thereby maintaining high electrical conductivity of the battery; secondly, the appropriate solvent ratio is conducive to the formation of a stable and dense interface film, promoting the formation of the SEI / CEI film and reducing side reactions; in addition, it also helps to ensure that the electrolyte has appropriate viscosity, electrical conductivity and chemical stability, and stable lithium ion transmission can be maintained even under low temperature or high temperature conditions, improving the charging and discharging efficiency, stability and safety of the lithium ion battery.

[0060] The mass fraction of the organic solvent in the electrolyte is 80% to 90%, for example, 80%, 82%, 84%, 86%, 88%, 90%, or a range formed by any two of them.

[0061] Through the synergistic effect of the lithium salt, the electrolyte additive composition and the organic solvent, the viscosity and electrical conductivity of the electrolyte can be optimized, and good stability can be maintained, thereby improving the charging and discharging performance and energy efficiency of the battery in high and low temperature environments.

[0062] This application does not limit the proportion of each additive in the electrolyte, as long as the above requirements are met. For example, in some embodiments, the mass fraction of the electrolyte functional additive in the electrolyte is 0.3% to 1%. By limiting the addition amount of the electrolyte functional additive, it can not only play its role in improving severe capacity decay and voltage drop, but also avoid changes in electrolyte viscosity or increased costs, which helps to achieve electrolyte formulation optimization and lithium-ion battery performance improvement.

[0063] In some embodiments, the mass fraction of the electrolyte functional additive in the electrolyte is 0.3% to 1%, for example, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, or a range consisting of any two thereof. By limiting the amount of the electrolyte functional additive added, the role of the electrolyte functional additive can be maximized, effectively improving the capacity retention rate and reducing the voltage drop when the battery is cycled under high voltage, thereby achieving electrolyte formulation optimization and improving the electrochemical performance of the battery.

[0064] In some embodiments, the mass fraction of the lithium salt additive in the electrolyte is 0.5% to 1%, for example, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, or any two thereof. The lithium salt additive can participate in the electrochemical reaction. By limiting the amount of the lithium salt additive, in addition to maintaining stable output of the battery under high-voltage cycling and effectively reducing voltage drop, the energy density of the battery can also be increased.

[0065] In some embodiments, the mass fraction of the carbonate additive in the electrolyte is 0.1% to 1%, for example, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, or any combination thereof. By limiting the amount of carbonate additive added, the formation of a uniform and dense SEI film can be promoted, maximizing its multiple functions.

[0066] In some embodiments, the mass fraction of the sulfur-containing additive in the electrolyte is 0.5% to 3%, for example, 0.5%, 0.8%, 1%, 1.2%, 1.5%, 1.8%, 2%, 2.2%, 2.5%, 2.8%, 3%, or any combination thereof. By limiting the amount of the sulfur-containing additive, the effectiveness of the additive can be ensured while also considering cost.

[0067] The specific type of the organic solvent is not limited in the present application, and can be a conventional organic solvent in the art. In some embodiments, the organic solvent comprises at least one of a cyclic carbonate, a chain carbonate, and a chain carboxylate. In some preferred embodiments, the organic solvent comprises a cyclic carbonate, a chain carbonate, and a chain carboxylate, so that the advantages of the cyclic carbonate, the chain carbonate, and the chain carboxylate can be integrated, and the overall performance of the battery can be improved. Specifically, the cyclic carbonate can still maintain good electrical conductivity at low temperatures, and can promote the formation of a stable SEI film at low temperatures. The chain carbonate and the chain carboxylate can help to reduce the viscosity and have better stability at high temperatures. In this way, by limiting the specific type of the organic solvent, the stability of the electrolyte at high and low temperatures can be improved, the capacity retention rate of the battery during high and low temperature cycling can be considered, and the needs of the battery in different application scenarios can be met.

[0068] When the organic solvent comprises a cyclic carbonate, a chain carbonate, and a chain carboxylate, the mass ratio of the cyclic carbonate, the chain carbonate, and the chain carboxylate is (1-15):(20-70):(5-20). By limiting the ratio of the cyclic carbonate, the chain carbonate, and the chain carboxylate, the electrolyte formula can be optimized, and the balance of lithium ion transmission rate, SEI / CEI film formation, high and low temperature performance, cost effectiveness, internal resistance reduction, chemical stability, and battery safety can be considered.

[0069] The specific preparation method of the electrolyte is not limited in the present application, as long as the electrolyte contains the above components. For example, the specific preparation method of the electrolyte comprises the following steps: under a protective atmosphere, adding an electrolyte additive composition to an organic solvent, then adding a lithium salt, stirring and mixing at a first temperature to obtain an electrolyte; wherein the protective atmosphere can be argon, and the first temperature can be 5-15°C.

[0070] In a fourth aspect, the present application provides a battery comprising the electrolyte provided in the third aspect.

[0071] Due to the inclusion of the above electrolyte, the battery has excellent cycle stability, especially a high capacity retention rate and a low voltage drop when cycled under high voltage conditions. In addition, the battery can meet the needs of different temperature scenarios.

[0072] In some embodiments, the battery further comprises a negative electrode sheet containing a negative electrode active material and a positive electrode sheet containing a positive electrode active material.

[0073] The negative electrode sheet comprises a negative electrode current collector and a negative electrode active layer formed of a negative electrode active material arranged on the surface of the negative electrode current collector.

[0074] In particular, when the negative electrode sheet is prepared, the negative electrode active material, the first conductive agent, and the first binder are dispersed in an appropriate amount of solvent, and are sufficiently stirred and mixed to form a uniform negative electrode slurry. The negative electrode slurry is uniformly coated on the negative electrode current collector, and is subjected to drying, rolling, and slitting to obtain the negative electrode sheet. In a particular embodiment, the negative electrode active layer includes 70% to 99% of the graphite negative electrode material, 0.5% to 15% of the conductive agent, and 0.5% to 15% of the binder in terms of mass percentage.

[0075] In particular, when the negative electrode sheet is prepared, the negative electrode active material, the first conductive agent, and the first binder are dispersed in an appropriate amount of solvent, and are sufficiently stirred and mixed to form a uniform negative electrode slurry. The negative electrode slurry is uniformly coated on the negative electrode current collector, and is subjected to drying, rolling, and slitting to obtain the negative electrode sheet. In a particular embodiment, the negative electrode active layer includes 70% to 99% of the graphite negative electrode material, 0.5% to 15% of the conductive agent, and 0.5% to 15% of the binder in terms of mass percentage.

[0076] The present application does not limit the specific type of the negative electrode active material in the negative electrode sheet, which can be a negative electrode active material commonly used in batteries at present, such as at least one of graphite, hard carbon, soft carbon, mesocarbon microbeads, and silicon-based negative electrode material. In some preferred embodiments, the negative electrode active material includes a carbon-based negative electrode material.

[0077] The positive electrode sheet includes a positive electrode current collector and a positive electrode active layer formed of a positive electrode active material arranged on the surface of the positive electrode current collector.

[0078] In particular, when the negative electrode sheet is prepared, the negative electrode active material, the first conductive agent, and the first binder are dispersed in an appropriate amount of solvent, and are sufficiently stirred and mixed to form a uniform negative electrode slurry. The negative electrode slurry is uniformly coated on the negative electrode current collector, and is subjected to drying, rolling, and slitting to obtain the negative electrode sheet. In a particular embodiment, the negative electrode active layer includes 70% to 99% of the graphite negative electrode material, 0.5% to 15% of the conductive agent, and 0.5% to 15% of the binder in terms of mass percentage.

[0079] In particular, when the negative electrode sheet is prepared, the negative electrode active material, the first conductive agent, and the first binder are dispersed in an appropriate amount of solvent, and are sufficiently stirred and mixed to form a uniform negative electrode slurry. The negative electrode slurry is uniformly coated on the negative electrode current collector, and is subjected to drying, rolling, and slitting to obtain the negative electrode sheet. In a particular embodiment, the negative electrode active layer includes 70% to 99% of the graphite negative electrode material, 0.5% to 15% of the conductive agent, and 0.5% to 15% of the binder in terms of mass percentage.

[0080] The application does not limit the specific type of positive electrode active material in the positive electrode sheet, which can be the positive electrode active material commonly used in current batteries, such as at least one composite oxide of lithium and at least one of the metals of cobalt, nickel, and manganese, and combinations thereof. Specifically, it can be at least one of lithium cobaltate, lithium nickelate, lithium manganate, nickel-cobalt-manganese ternary material, nickel-cobalt-aluminum ternary material, lithium iron phosphate, lithium nickel-manganese oxide, and lithium-rich manganese-based material. In some preferred embodiments, the positive electrode active material is Li2MnO3, LiMn 0.375 Ni 0.375 Co 0.25 O2, wherein the mass ratio of Li2MnO3, LiMn 0.375 Ni 0.375 Co 0.25 O2 is (0-25):(75-100).

[0081] The battery also includes a separator. The application does not limit the specific selection of the separator material, which can be the separator material commonly used in current batteries, such as polypropylene separator, polyethylene separator, polypropylene / polyethylene double-layer composite separator, polypropylene / polyethylene / polypropylene (PP / PE / PP) three-layer composite separator, etc.

[0082] In the preparation of the battery, the positive electrode sheet, the separator, and the negative electrode sheet are wound or laminated to obtain an electric core, the electric core is packaged into an aluminum-plastic film pre-punched and formed, and after the packaged battery is dried, the electrolyte is injected into the dried battery. After the battery is aged, formed, and twice sealed, the preparation of the battery is completed.

[0083] The application will be further described in detail below in conjunction with specific examples, which cannot be understood as limiting the scope of the application claimed. If the specific conditions are not specified in the examples, they are carried out according to the conventional conditions or the conditions recommended by the manufacturer. If the reagents or instruments used are not specified by the manufacturer, they are all conventional products that can be purchased on the market.

[0084] Example 1

[0085] The electrolyte of this embodiment is composed of an organic solvent, a lithium salt, and an additive; the additive includes vinylene carbonate, lithium difluorophosphate, 1,3-propane sultone, and a functional additive as shown in Formula 1, CAS No. 95715-48-3;

[0086] wherein the mass fraction of vinylene carbonate in the electrolyte is 0.5%, the mass fraction of lithium difluorophosphate in the electrolyte is 0.5%, the mass fraction of 1,3-propane sultone in the electrolyte is 2%, and the mass fraction of the functional additive in the electrolyte is 0.3%;

[0087]

[0088] The lithium salt is lithium hexafluorophosphate, and the mass fraction of lithium hexafluorophosphate in the electrolyte is 15%; the mass fraction of the organic solvent in the electrolyte is 81.7%, and the organic solvent is composed of fluoroethylene carbonate, ethylene carbonate, ethyl difluoroacetate and diethyl carbonate, wherein the mass fraction of fluoroethylene carbonate is 10%, the mass fraction of ethylene carbonate is 10%, the mass fraction of ethyl difluoroacetate is 15%, and the mass fraction of diethyl carbonate is 65%, based on the total mass of the organic solvent being 100%.

[0089] The preparation method of the electrolyte of the embodiment includes: under the atmosphere of argon, adding the formula amount of vinylene carbonate, lithium difluorophosphate, 1,3-propane sultone and functional additives into the organic solvent according to the above mass fractions, and then adding lithium hexafluorophosphate, stirring and mixing at a temperature of 10°C to obtain the electrolyte of the embodiment.

[0090] Example 2

[0091] The difference from Example 1 is that the mass fraction of vinylene carbonate in the electrolyte is 0.2%, and the mass fraction of the organic solvent is 82%.

[0092] Example 3

[0093] The difference from Example 1 is that the mass fraction of vinylene carbonate in the electrolyte is 0.8%, and the mass fraction of the organic solvent is 81.4%.

[0094] Example 4

[0095] The difference from Example 1 is that the mass fraction of lithium difluorophosphate in the electrolyte is 0.2%, and the mass fraction of the organic solvent is 82%.

[0096] Example 5

[0097] The difference from Example 1 is that the mass fraction of lithium difluorophosphate in the electrolyte is 0.8%, and the mass fraction of the organic solvent is 81.4%.

[0098] Example 6

[0099] The difference from Example 1 is that the mass fraction of 1,3-propane sultone in the electrolyte is 0.5%, and the mass fraction of the organic solvent is 83.2%.

[0100] Example 7

[0101] The difference from Example 1 is that the mass fraction of 1,3-propane sultone in the electrolyte is 3%, and the mass fraction of the organic solvent is 80.5%.

[0102] Example 8

[0103] The difference from Example 1 is that the mass fraction of the functional additive is 0.1%, and the mass fraction of the organic solvent is 81.9%.

[0104] Example 9

[0105] The difference from Example 1 is that the mass fraction of the functional additive is 0.5%, and the mass fraction of the organic solvent is 81.5%.

[0106] Example 10

[0107] The difference from Example 1 is that the mass fraction of the functional additive in the electrolyte is 1%, and the mass fraction of the organic solvent is 81%.

[0108] Example 11

[0109] The difference from Example 1 is that the mass fraction of the functional additive in the electrolyte is 1.5%, and the mass fraction of the organic solvent is 80.5%.

[0110] Example 12

[0111] The difference from Example 1 is that no vinylene carbonate, lithium difluorophosphate, 1,3-propanesultone is added, and the mass fraction of the organic solvent is 84.7%.

[0112] Example 13

[0113] The difference from Example 1 is that no lithium difluorophosphate, 1,3-propanesultone is added, and the mass fraction of the organic solvent is 84.2%.

[0114] Example 14

[0115] The difference from Example 1 is that no vinylene carbonate, 1,3-propanesultone is added, and the mass fraction of the organic solvent is 84.2%.

[0116] Example 15

[0117] The difference from Example 1 is that no vinylene carbonate, lithium difluorophosphate is added, and the mass fraction of the organic solvent is 82.7%.

[0118] Comparative Example 1

[0119] The difference from Example 1 is that no functional additive is added, and the mass fraction of the organic solvent is 82%.

[0120] Comparative Example 2

[0121] The difference from Example 1 is that the functional additive is replaced by a structure as shown in Formula 2:

[0122]

[0123] Comparative Example 3

[0124] The difference from Example 1 is that the functional additive is replaced with a structure as shown in Formula 3:

[0125]

[0126] Comparative Example 4

[0127] The difference from Example 1 is that the functional additive is replaced with a structure as shown in Formula 4:

[0128]

[0129] Test example

[0130] The electrolytes of the examples and comparative examples were applied to lithium-ion batteries, and the performance of the lithium-ion batteries was tested. The specific preparation method of the lithium-ion battery includes: mixing graphite, acetylene black, carboxymethyl cellulose, and styrene-butadiene rubber in a mass ratio of 94:1:2:3 to form a negative electrode slurry; coating the negative electrode slurry on a copper foil current collector, and vacuum drying to produce a negative electrode sheet;

[0131] The positive electrode material (0.25Li2MnO3·0.75LiMn 0.375 Ni 0.375 Co 0.25 O2), acetylene black and polyvinylidene fluoride are mixed in a mass ratio of 94:3:3 to form a positive electrode slurry; the positive electrode slurry is coated on an aluminum foil current collector, and vacuum dried to obtain a positive electrode sheet;

[0132] The positive electrode sheet, Celgard 2400 separator and negative electrode sheet are wound or stacked to obtain a battery cell, and the battery cell is encapsulated in a pre-stamped aluminum-plastic film. After the encapsulated battery is dried to remove moisture, the electrolyte of the embodiment and the comparative example is injected into the dried battery. After the battery is aged, formed and sealed again, a lithium-ion battery is obtained.

[0133] The following electrochemical tests were performed using a Xinwei charge and discharge test cabinet.

[0134] (1) Normal temperature cycle performance test:

[0135] At 25°C, charge the lithium-ion battery at a constant current of 0.5C (nominal capacity) to a voltage of 4.6V, then charge at a constant voltage of 4.6V to a current of ≤0.05C. After 10 minutes of storage, discharge at a constant current of 1C to a cut-off voltage of 2.5V. This constitutes one charge-discharge cycle. Perform 1000 charge-discharge cycles of the lithium-ion battery under the above conditions.

[0136] The capacity retention rate (%) of the lithium ion battery after 1000 cycles = (discharge capacity of the 1000th cycle / initial discharge capacity) x 100%.

[0137] The average voltage (V) of the lithium ion battery after 1000 cycles = discharge energy of the 1000th cycle / discharge capacity of the 1000th cycle.

[0138] (2) High-temperature cycle performance test

[0139] The lithium ion battery was charged at 45°C at 1.0C (nominal capacity) to a voltage of 4.6V, then charged at 4.6V to a current ≤0.05C, and after a 10 min rest, discharged at 1C to a cut-off voltage of 2.5V, which was one charge-discharge cycle. The lithium ion battery was subjected to 800 charge-discharge cycles under the above conditions.

[0140] The capacity retention rate (%) of the lithium ion battery after 800 cycles = (discharge capacity of the 800th cycle / initial discharge capacity) x 100%.

[0141] The average voltage (V) of the lithium ion battery after 800 cycles = discharge energy of the 800th cycle / discharge capacity of the 800th cycle.

[0142] The test results are shown in Table 1.

[0143] Table 1

[0144]

[0145] As can be seen from Comparative Examples 1-15 and Comparative Example 1, by introducing the functional additive shown as Formula 1, the cycle performance and voltage drop can be significantly improved.

[0146] As can be seen from Comparative Examples 1-15 and Comparative Examples 2-4, although the functional additive of Comparative Example 2 also contains a C=C bond, a C=O bond and a cyclic structure, the functional additive of Comparative Example 3 contains a carbon-nitrogen bond, a C=O bond and a cyclic structure, and the functional additive of Comparative Example 4 contains a pyridine nitrogen, a C=O bond and a cyclic structure, but the improvement in cycle performance and voltage drop is limited, and the capacity retention rate and the degree of reducing voltage drop of Examples 1-15 after 1000 cycles at room temperature and 800 cycles at high temperature are all greater than those of Comparative Examples 2-4. Therefore, it can be seen that the functional additive having the structural formula shown as Formula 1 in the present application is not the independent action of a single functional group, but the entire structure produces a synergistic effect in the electrolyte, and this synergistic effect is the key to improving the performance and stability of the battery.

[0147] Comparing Examples 1 to 15, it can be seen that Example 4 does not meet the mass ratio of lithium salt additive to electrolyte functional additive of (0.5-1): (0.3-1), Example 8 has a low amount of functional additive, and Example 11 has a high amount of functional additive, so the improvement is not as good as that of Examples 1 to 3, 5 to 7, and Example 10. By limiting the mass fraction of each component to a specific range, the battery's cycle capacity retention rate at high voltage can be further improved and the voltage drop can be reduced.

[0148] The above description is merely a preferred embodiment of the present application and is not intended to limit the present application. Various modifications and variations are possible for those skilled in the art. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present application shall be included within the scope of protection of the present application.

Claims

1. An electrolyte additive composition, characterized in that The electrolyte additive composition includes a lithium salt additive and an electrolyte functional additive. The structural formula of the electrolyte functional additive is shown in Formula 1: Formula 1.

2. The electrolyte additive composition according to claim 1, characterized in that The mass ratio of the lithium salt additive to the electrolyte functional additive is (0.5-1): (0.3-1).

3. The electrolyte additive composition according to claim 2, characterized in that The electrolyte additive composition further includes a carbonate additive; the mass ratio of the carbonate additive to the electrolyte functional additive is (0.1-1): (0.3-1); The carbonate additive includes at least one of vinylene carbonate and fluoroethylene carbonate; The lithium salt additive includes at least one of lithium bis(fluorosulfonyl)imide, lithium difluorophosphate, lithium borate, lithium difluoroborate, and lithium hexafluorophosphate.

4. The electrolyte additive composition according to claim 2 or 3, characterized in that The electrolyte additive composition further includes a sulfur-containing additive; the mass ratio of the sulfur-containing additive to the electrolyte functional additive is (0.5-3): (0.3-1); The sulfur-containing additive includes at least one of propylene sulfite, 1,3-propane sultone, and ethylene sulfate.

5. An electrolyte, characterized in that The electrolyte comprises a lithium salt, an organic solvent and the electrolyte additive composition according to any one of claims 2 to 4.

6. The electrolyte according to claim 5, characterized in that The mass fraction of the lithium salt in the electrolyte is 10% to 15%; and / or, The mass fraction of the organic solvent in the electrolyte is 80% to 90%; and / or, The mass fraction of the electrolyte additive composition in the electrolyte is greater than 0 and less than or equal to 5%.

7. The electrolyte according to claim 5 or 6, characterized in that The mass fraction of the electrolyte functional additive in the electrolyte is 0.3% to 1%; and / or, The mass fraction of the lithium salt additive in the electrolyte is 0.5% to 1%; and / or, The mass fraction of the carbonate additive in the electrolyte is 0.1-1%; and / or, The mass fraction of the sulfur-containing additive in the electrolyte is 0.5% to 3%.

8. The electrolyte according to claim 5 or 6, characterized in that The organic solvent includes at least one of cyclic carbonate, chain carbonate, and chain carboxylate.

9. The electrolyte according to claim 5 or 6, characterized in that The organic solvent includes a cyclic carbonate, a chain carbonate and a chain carboxylate, wherein the mass ratio of the cyclic carbonate, the chain carbonate and the chain carboxylate is (1-15): (20-70): (5-20).

10. A battery, characterized in that: The battery comprises the electrolyte according to any one of claims 5 to 9.

11. The battery according to claim 10, characterized in that The battery also includes a negative electrode sheet containing a negative electrode active material; The battery also includes a positive electrode sheet containing a positive electrode active material; The negative electrode active material includes a carbon-based negative electrode material; the positive electrode active material includes Li2MnO3, LiMn 0.375 Ni 0.375 Co 0.25 At least one of O2.

12. The battery according to claim 11, characterized in that The positive electrode active material is Li2MnO3, LiMn 0.375 Ni 0.375 Co 0.25 O2 mixture, including Li2MnO3, LiMn 0.375 Ni 0.375 Co 0.25 The mass ratio of O2 is (0~25):(75~100).

Images