Electrolyte additive, electrolyte and battery

Abstract

An electrolyte additive, an electrolyte and a battery. The electrolyte additive comprises a compound as represented by formula 1 and a lithium salt additive containing an oxalic acid group, wherein the mass ratio of the compound as represented by formula 1 to the lithium salt additive containing an oxalic acid group is 1:(0.5-2.6); and the lithium salt additive containing an oxalic acid group comprises at least one of a lithium oxalate phosphate additive and a lithium oxalate borate additive.

Description

Electrolyte additives, electrolytes and batteries

[0001] This application claims priority to the Chinese patent application filed with the China Patent Office on December 8, 2023, with application number 2023116781344 and application name “Electrolyte Additives, Electrolytes and Batteries”, the entire contents of which are incorporated by reference into this application. Technical Field

[0002] The present invention belongs to the field of batteries, and in particular relates to an electrolyte additive, an electrolyte and a battery. Background Art

[0003] Lithium-ion batteries are widely used in power, energy storage, aerospace, digital and other fields due to their advantages such as high voltage, large capacity, no memory effect and long life. In recent years, lithium-ion batteries have achieved great success in the field of high-energy batteries, but consumers still expect batteries with higher comprehensive performance. High-comprehensive performance batteries depend on the research and development of new electrode materials and electrolyte systems. However, factors such as the dissolution of positive electrode metal ions, the occurrence of electrolyte side reactions, and the degradation of the electrode-electrolyte interface under high temperature conditions lead to serious gas production in lithium-ion batteries, making it difficult to improve the overall performance of lithium batteries. In order to solve the problem of high-temperature gas production in lithium batteries, film-forming additives are usually used to regulate the formation of a stable SEI film at the electrode-electrolyte interface. However, the SEI films formed by such additives are relatively thick or have poor ion conductivity, resulting in a large impedance of the lithium battery, which makes the battery cycle performance and low-temperature performance poor.

[0004] Vinyl sulfate electrolyte additives can reduce the initial impedance of lithium batteries while improving the high-temperature performance of lithium batteries. Vinyl sulfate (DTD) is a representative compound of this type of additive. It can form an electrode-electrolyte interface film rich in sulfate esters and sulfates. When the ambient temperature is above 45°C, it still has an excellent effect in inhibiting battery gas production. However, DTD raw materials have poor stability and easily cause electrolyte discoloration and increased acidity. Therefore, DTD raw materials and their electrolytes are very difficult to store. Therefore, it is very important to find electrolyte additives with stable performance and significant improvement in battery performance.

[0005] Summary of the Invention

[0006] The present invention aims to at least partially address one of the technical problems in the related art. To this end, one object of the present invention is to provide an electrolyte additive, an electrolyte, and a battery. Adding this electrolyte additive to a battery electrolyte can improve the cycling performance, low-temperature discharge performance, and high-temperature storage performance of a lithium battery.

[0007] The first aspect of the present invention provides an electrolyte additive, comprising a compound represented by Formula 1 and a lithium salt additive containing an oxalic acid group.

[0008] The electrolyte additive of the present invention comprises a compound represented by Formula 1 and a lithium salt additive containing an oxalic acid group. When the electrolyte additive is added to a lithium ion battery, during the formation and circulation process, the compound represented by Formula 1 undergoes a ring-opening reaction to obtain a highly active free radical product A. The addition of lithium salt additives containing oxalic acid groups, because they contain oxalic acid groups, lithium salt additives containing oxalic acid groups are easy to form free radical compounds under the conditions of gaining and losing electrons, so they can react with product A to form free radicals, thereby blocking the product A of the ring-opening reaction of the compound shown in Formula 1 from activating the ethylene carbonate (EC) molecules in the electrolyte, avoiding the gas production problem caused by the ring-opening reaction of the EC molecules, thereby enhancing the high-temperature storage performance of the lithium battery. The presence of the benzene ring in the compound shown in Formula 1 can significantly reduce the reaction energy barrier, which is conducive to the ring-opening reaction of the compound shown in Formula 1 during the formation stage of the lithium battery, making it easier to form an SEI film rich in inorganic sulfate and / or inorganic sulfite and / or alkyl sulfonate lithium and / or alkyl sulfate lithium. At the same time, the presence of the benzene ring in the compound shown in Formula 1 makes the formed SEI film have excellent stability, enhances the stability and ionic conductivity at the negative electrode-electrolyte interface, significantly reduces the DC internal resistance of the battery, and improves the cycle performance and low-temperature discharge performance of the lithium-ion battery. In addition, lithium salt additives containing oxalic acid groups can also increase the concentration of free lithium ions in the electrolyte, replenishing the lithium ions consumed during the formation of the SEI film, thereby improving the initial capacity and initial charge and discharge efficiency of the battery. Therefore, adding this electrolyte additive to the battery electrolyte can improve the cycling performance, low-temperature discharge performance, and high-temperature storage performance of lithium batteries.

[0009] In some embodiments, the mass ratio of the compound represented by Formula 1 to the lithium salt additive containing an oxalic acid group is 1:(0.5-2.6). This can improve the cycle performance, low-temperature discharge performance, and high-temperature storage performance of the lithium battery.

[0010] In some embodiments, the oxalic acid group-containing lithium salt additive includes at least one of an oxalophosphate lithium salt additive and an oxaloborate lithium salt additive, thereby enhancing the high-temperature storage performance of the lithium battery.

[0011] In some embodiments, the lithium oxalate phosphate additive includes at least one of lithium trioxalate phosphate, lithium difluorodioxalate phosphate, and lithium tetrafluorooxalate phosphate, thereby enhancing the high-temperature storage performance of the lithium battery.

[0012] In some embodiments, the mass ratio of the compound represented by Formula 1 to the lithium oxalate phosphate additive is 1:(0.5-2.6). This can improve the cycle performance, low-temperature discharge performance, and high-temperature storage performance of the lithium battery.

[0013] In some embodiments, the lithium oxalatoborate salt additive includes at least one of lithium bis(oxalatoborate) and lithium difluoro(oxalatoborate), thereby enhancing the high-temperature storage performance of the lithium battery.

[0014] In some embodiments, the mass ratio of the compound represented by Formula 1 to the lithium oxalate borate salt additive is 1:(0.8-1.3). This can improve the cycle performance, low-temperature discharge performance, and high-temperature storage performance of the lithium battery.

[0015] The second aspect of the present invention provides an electrolyte comprising the electrolyte additive of the first aspect. Thus, when the electrolyte is added to a lithium battery, the cycling performance, low-temperature discharge performance, and high-temperature storage performance of the lithium battery can be improved.

[0016] In some embodiments, the mass of the compound represented by Formula 1 accounts for 0.1% to 2% of the total mass of the electrolyte, thereby improving the cycle performance and low-temperature discharge performance of the lithium battery.

[0017] In some embodiments, the mass of the lithium salt additive containing oxalic acid groups accounts for 0.1% to 2% of the total mass of the electrolyte, thereby improving the high-temperature storage performance of the lithium battery.

[0018] In some embodiments, the electrolyte further includes a solvent, and the solvent includes ethylene carbonate.

[0019] In some embodiments, the mass proportion of the ethylene carbonate in the electrolyte is 25% to 30%.

[0020] The third aspect of the present invention provides a battery comprising the electrolyte described in the second aspect, thereby having excellent cycle performance, low-temperature discharge performance, and high-temperature storage performance.

[0021] Additional aspects and advantages of the present invention will be set forth in part in the description which follows and, in part, will be obvious from the description which follows, or may be learned by practice of the present invention. DETAILED DESCRIPTION

[0022] The embodiments of the present invention are described in detail below, which are intended to explain the present invention but are not to be construed as limiting the present invention.

[0023] The technical solution of this application is completed by the inventor based on the following discovery: the compound shown in Formula 1 can regulate the formation of a stable SEI film containing inorganic sulfate, inorganic sulfite, alkyl lithium sulfonate, alkyl lithium sulfate and other components at the electrode-electrolyte interface, which can enhance the stability and ionic conductivity at the electrode-electrolyte interface, greatly reduce the DC internal resistance of the battery, and enhance the cycle performance and low-temperature discharge performance of the lithium-ion battery. However, if only the compound shown in Formula 1 is added to the electrolyte, it cannot guarantee the initial capacity and the first charge and discharge efficiency of the lithium battery; at the same time, it cannot suppress the battery expansion during high-temperature storage and the capacity retention rate is low. This is mainly because, on the one hand, the compound shown in Formula 1 is more likely to undergo a ring-opening reaction in the lithium battery formation stage to form an SEI film rich in inorganic sulfate and / or inorganic sulfite and / or alkyl lithium sulfonate and / or alkyl lithium sulfate, but while forming the SEI film, it consumes more lithium ions in the electrolyte, resulting in a decrease in the initial capacity and the first charge and discharge efficiency. On the other hand, the product A obtained after the ring-opening reaction of the compound shown in Formula 1 is a highly active free radical, which can activate EC molecules in the electrolyte. The specific process of product A activating EC molecules is as follows: Then, product A promotes the ring-opening decomposition of EC to form gases such as carbon dioxide and ethylene. This process is more intense under high temperature conditions, causing the battery volume to expand, resulting in poor high-temperature storage performance of the lithium battery. At the same time, EC easily forms alkyl lithium carbonate, lithium carbonate, etc. after ring-opening decomposition. This process also consumes lithium ions in the electrolyte, thus having a negative impact on the initial capacity and initial charge and discharge efficiency of the lithium battery.

[0024] In view of this, in a first aspect of the present invention, the present invention provides an electrolyte additive, comprising a compound represented by Formula 1 and a lithium salt additive containing an oxalic acid group.

[0025] The electrolyte additive is added to the lithium ion battery. During the formation and circulation process, the compound shown in formula 1 undergoes a ring-opening reaction to obtain a highly active free radical product A. The addition of lithium salt additives containing oxalic acid groups, because they contain oxalic acid groups, lithium salt additives containing oxalic acid groups are easy to form free radical compounds under the conditions of gaining and losing electrons, so they can react with product A to form free radicals, thereby blocking the product A of the ring-opening reaction of the compound shown in Formula 1 from activating the ethylene carbonate (EC) molecules in the electrolyte, avoiding the gas production problem caused by the ring-opening reaction of the EC molecules, thereby enhancing the high-temperature storage performance of the lithium battery. The presence of the benzene ring in the compound shown in Formula 1 can significantly reduce the reaction energy barrier, which is conducive to the ring-opening reaction of the compound shown in Formula 1 during the formation stage of the lithium battery, making it easier to form an SEI film rich in inorganic sulfate and / or inorganic sulfite and / or alkyl sulfonate lithium and / or alkyl sulfate lithium. At the same time, the presence of the benzene ring in the compound shown in Formula 1 makes the formed SEI film have excellent stability, enhances the stability and ionic conductivity at the negative electrode-electrolyte interface, significantly reduces the DC internal resistance of the battery, and improves the cycle performance and low-temperature discharge performance of the lithium-ion battery. In addition, lithium salt additives containing oxalic acid groups can also increase the concentration of free lithium ions in the electrolyte, replenishing the lithium ions consumed during the formation of the SEI film, thereby improving the initial capacity and initial charge and discharge efficiency of the battery. Therefore, adding this electrolyte additive to the battery electrolyte can improve the cycling performance, low-temperature discharge performance, and high-temperature storage performance of lithium batteries.

[0026] In some embodiments of the present invention, the mass ratio of the compound of Formula 1 to the lithium salt additive containing an oxalic acid group is 1:(0.5-2.6). For example, the mass ratio of the compound of Formula 1 to the lithium salt additive containing an oxalic acid group is 1:0.5, 1:0.8, 1:1.1, 1:1.4, 1:1.7, 1:2.0, 1:2.3, 1:2.6, etc., or can be any range consisting of the above values. Therefore, the compound represented by Formula 1 and the lithium salt additive containing an oxalic acid group are compounded in the above-mentioned mass ratio, which not only forms a SEI film with excellent stability, enhances the stability and ionic conductivity at the electrode-electrolyte interface, significantly reduces the DC internal resistance of the battery, and improves the cycle performance and low-temperature discharge performance of the lithium-ion battery, but also increases the lithium ion concentration in the electrolyte, replenishes the consumption of lithium ions during the formation of the SEI film, and effectively blocks the highly active free radical product A obtained after the ring-opening reaction of the compound represented by Formula 1 from activating EC molecules, thereby preventing the EC molecules from undergoing a ring-opening reaction to form gases such as carbon dioxide and ethylene, reducing the battery volume expansion rate, and improving the high-temperature storage performance of the battery.

[0027] In some embodiments of the present invention, the lithium salt additive containing an oxalic acid group includes at least one of an oxalic acid lithium phosphate salt additive and an oxalic acid lithium borate salt additive. Thus, the oxalic acid lithium phosphate salt additive and the oxalic acid lithium borate salt additive can, on the one hand, increase the concentration of free lithium ions in the electrolyte and replenish the lithium ions consumed during the formation of the SEI film, thereby improving the initial capacity and the first charge and discharge efficiency of the battery; on the other hand, the oxalic acid groups in the oxalic acid lithium phosphate salt additive and the oxalic acid lithium borate salt additive are easy to form free radical compounds under the conditions of gaining and losing electrons, and thus can react with the product A of the ring-opening reaction of the compound shown in Formula 1. A free radical reaction occurs, thereby preventing Product A from activating ethylene carbonate (EC) molecules in the electrolyte, avoiding the gas production problem caused by the ring-opening reaction of EC molecules, thereby enhancing the high-temperature storage performance of the lithium battery. At the same time, the compound represented by Formula 1 is compounded with this type of lithium salt additive containing oxalic acid groups to form a SEI film with excellent stability, enhancing the stability and ionic conductivity at the electrode-electrolyte interface, significantly reducing the battery's DC internal resistance, and improving the cycling performance and low-temperature discharge performance of the lithium-ion battery.

[0028] In some embodiments of the present invention, the lithium oxalate phosphate salt additive includes at least one of lithium trioxalate phosphate, lithium difluorodioxalate phosphate, and lithium tetrafluorooxalate phosphate.

[0029] Therefore, the use of lithium oxalate phosphate salt additives can not only increase the concentration of free lithium ions in the electrolyte, replenish the lithium ions consumed in the formation of the SEI film, and improve the initial capacity and first charge and discharge efficiency of the battery; but also the oxalic acid groups in the lithium oxalate phosphate salt additives are easy to form free radical compounds under the conditions of gaining and losing electrons, and thus can react with the product A of the ring-opening reaction of the compound shown in Formula 1. A free radical reaction occurs, thereby preventing Product A from activating ethylene carbonate (EC) molecules in the electrolyte, avoiding the gas production caused by the ring-opening reaction of EC molecules, thereby enhancing the high-temperature storage performance of the lithium battery. At the same time, the compound represented by Formula 1 is compounded with lithium oxalate phosphate salt additives to form a SEI film with excellent stability, enhancing the stability and ionic conductivity of the electrode-electrolyte interface, significantly reducing the battery's DC internal resistance, and improving the cycling performance and low-temperature discharge performance of the lithium-ion battery.

[0030] In some embodiments of the present invention, the mass ratio of the compound of Formula 1 to the lithium oxalate phosphate additive is 1: (0.5-2.6). For example, the mass ratio of the compound of Formula 1 to the lithium oxalate phosphate additive is 1: 0.5, 1: 0.8, 1: 1.1, 1: 1.4, 1: 1.7, 1: 2.0, 1: 2.3, 1: 2.6, etc., or can be a range consisting of any of the above numerical values. Therefore, the compound of Formula 1 and the lithium oxalate phosphate additive are compounded in the above mass ratio, which can not only form a SEI film with excellent stability, enhance the stability and ionic conductivity at the electrode-electrolyte interface, significantly reduce the DC internal resistance of the battery, improve the cycle performance and low-temperature discharge performance of the lithium-ion battery, but also increase the lithium ion concentration in the electrolyte, supplement the consumption of lithium ions during the formation of the SEI film, and effectively block the highly active free radical product A obtained after the ring-opening reaction of the compound of Formula 1 Activate EC molecules to prevent ring-opening reactions of EC molecules to form gases such as carbon dioxide and ethylene, reduce the volume expansion rate of the battery, and improve the high-temperature storage performance of the battery.

[0031] In some embodiments of the present invention, the lithium oxalate borate salt additive includes at least one of lithium bis(oxalate borate) and lithium difluoro(oxalate borate). The central boron atom of the lithium oxalate borate salt additive has an empty orbital and a certain degree of electron deficiency, which can accept the lone electron on the highly active free radical product obtained after the ring-opening reaction of the compound shown in Formula 1, thereby blocking the product A obtained after the ring-opening reaction of the compound shown in Formula 1. Deactivating EC molecules prevents them from undergoing a ring-opening reaction to form gases such as carbon dioxide and ethylene. Furthermore, the oxalic acid groups in lithium oxalate borate salt additives readily form free radical compounds under conditions of electron gain and loss. Therefore, they can react with the highly active free radical product obtained after the ring-opening reaction of the compound represented by Formula 1 to undergo a free radical reaction, thereby preventing the ring-opening reaction product A of the compound represented by Formula 1 from activating EC molecules in the electrolyte and avoiding the gas production problem caused by the ring-opening reaction of EC molecules. Furthermore, the compound represented by Formula 1 combined with lithium oxalate borate salt additives can form a SEI film with excellent stability, enhancing the stability and ionic conductivity at the electrode-electrolyte interface, significantly reducing the battery's DC internal resistance, and improving the cycling performance and low-temperature discharge performance of lithium-ion batteries. Therefore, the use of lithium oxalate borate salt additives can increase the concentration of free lithium ions in the electrolyte, replenishing the lithium ions consumed during the SEI film formation process, increasing the battery's initial capacity and initial charge and discharge efficiency, while also reducing the battery's volume expansion rate and improving the battery's high-temperature storage performance and low-temperature discharge performance.

[0032] In some embodiments of the present invention, the mass ratio of the compound represented by Formula 1 to the lithium oxalate borate salt additive is 1: (0.8 to 1.3). For example, the mass ratio of the compound represented by Formula 1 to the lithium oxalate borate salt additive is 1: 0.8, 1: 0.9, 1: 1.0, 1: 1.1, 1: 1.2, 1: 1.3, etc., or can be a range composed of any of the above numerical values. Therefore, the compound represented by Formula 1 and the lithium oxalate borate salt additive are compounded according to the above mass ratio, which can not only form a SEI film with excellent stability, enhance the stability and ionic conductivity at the electrode-electrolyte interface, significantly reduce the DC internal resistance of the battery, improve the cycle performance and low-temperature discharge performance of the lithium-ion battery, but also increase the lithium ion concentration in the electrolyte, supplement the consumption of lithium ions during the formation of the SEI film, and effectively block the highly active free radical product A obtained after the ring-opening reaction of the compound represented by Formula 1 Activate EC molecules to prevent ring-opening reactions of EC molecules to form gases such as carbon dioxide and ethylene, reduce the volume expansion rate of the battery, and improve the high-temperature storage performance of the battery.

[0033] The second aspect of the present invention provides an electrolyte comprising the electrolyte additive of the first aspect. Thus, adding the electrolyte to a lithium battery can improve the cycle performance, low-temperature discharge performance, and high-temperature storage performance of the lithium battery.

[0034] In some embodiments of the present invention, the mass percentage of the compound represented by Formula 1 is 0.1% to 2% based on the total mass of the electrolyte. For example, the mass percentage of the compound represented by Formula 1 is 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, 2.0%, etc., or can be any range consisting of the above values.

[0035] In some embodiments of the present invention, the weight percentage of the lithium salt additive containing an oxalic acid group is 0.1% to 2% based on the total weight of the electrolyte. For example, the weight percentage of the lithium salt additive containing an oxalic acid group is 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, 2.0%, etc., or can be any range consisting of the above values.

[0036] Thus, the compound of formula 1 and the lithium salt additive containing oxalic acid group are added to the electrolyte at the above concentration. During the formation and circulation process, the compound of formula 1 undergoes a ring-opening reaction to obtain a highly active free radical product A. The addition of lithium salt additives containing oxalic acid groups, because they contain oxalic acid groups, lithium salt additives containing oxalic acid groups are easy to form free radical compounds under the conditions of gaining and losing electrons, so they can react with product A to form free radicals, thereby blocking the product A of the ring-opening reaction of the compound shown in Formula 1 from activating the ethylene carbonate (EC) molecules in the electrolyte, avoiding the gas production problem caused by the ring-opening reaction of the EC molecules, thereby enhancing the high-temperature storage performance of the lithium battery. The presence of the benzene ring in the compound shown in Formula 1 can significantly reduce the reaction energy barrier, which is conducive to the ring-opening reaction of the compound shown in Formula 1 during the formation stage of the lithium battery, making it easier to form an SEI film rich in inorganic sulfate and / or inorganic sulfite and / or alkyl sulfonate lithium and / or alkyl sulfate lithium. At the same time, the presence of the benzene ring in the compound shown in Formula 1 makes the formed SEI film have excellent stability, enhances the stability and ionic conductivity at the negative electrode-electrolyte interface, significantly reduces the DC internal resistance of the battery, and improves the cycle performance and low-temperature discharge performance of the lithium-ion battery. In addition, lithium salt additives containing oxalic acid groups can also increase the concentration of free lithium ions in the electrolyte, replenishing the lithium ions consumed during the formation of the SEI film, thereby improving the initial capacity and initial charge and discharge efficiency of the battery. Therefore, adding this electrolyte additive to the battery electrolyte can improve the cycle performance, low-temperature discharge performance, and high-temperature storage performance of lithium batteries.

[0037] In some embodiments of the present invention, the electrolyte further comprises a solvent, and the solvent comprises ethylene carbonate.

[0038] In some embodiments of the present invention, the mass proportion of the ethylene carbonate in the electrolyte is 25% to 30%.

[0039] In some embodiments of the present application, the solvent may also include at least one of propylene carbonate, ethyl methyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butylene carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, cyclopentane, dimethyl sulfone, ethylene glycol dimethyl ether, methyl ethyl sulfone and diethyl sulfone.

[0040] In some embodiments of the present invention, the electrolyte may further include an electrolyte salt, and the electrolyte salt may include at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalatoborate, lithium dioxalatoborate, lithium difluorodioxalatophosphate, and lithium tetrafluorooxalatophosphate.

[0041] In some embodiments of the present application, the electrolyte may also include negative electrode film-forming additives, positive electrode film-forming additives, and additives that can improve certain battery properties, such as additives that improve battery overcharge performance, additives that improve battery high or low temperature performance, etc.

[0042] It should be noted that the negative electrode film-forming additives, positive electrode film-forming additives and additives that can improve certain battery properties are all types of additives commonly used in this field. Those skilled in the art can choose according to actual needs and will not be repeated here. The characteristics and advantages described for the above-mentioned electrolyte additives are also applicable to the electrolyte and will not be repeated here.

[0043] The third aspect of the present invention provides a battery comprising the electrolyte described in the second aspect.

[0044] Thus, the electrolyte additive is added to the lithium ion battery, and during the formation and circulation process, the compound shown in Formula 1 undergoes a ring-opening reaction to obtain a highly active free radical product A. The addition of lithium salt additives containing oxalic acid groups, because they contain oxalic acid groups, makes it easy for lithium salt additives containing oxalic acid groups to form free radical compounds under the conditions of gaining and losing electrons, so they can react with product A to form free radicals, thereby blocking the product A of the ring-opening reaction of the compound shown in Formula 1 from activating the ethylene carbonate (EC) molecules in the electrolyte, avoiding the gas production problem caused by the ring-opening reaction of the EC molecules, thereby enhancing the high-temperature storage performance of the lithium battery. The presence of the benzene ring in the compound shown in Formula 1 can significantly reduce the reaction energy barrier, which is conducive to the ring-opening reaction of the compound shown in Formula 1 during the formation stage of the lithium battery, making it easier to form an SEI film rich in inorganic sulfate and / or inorganic sulfite and / or alkyl sulfonate lithium and / or alkyl sulfate lithium. At the same time, the presence of the benzene ring in the compound shown in Formula 1 makes the formed SEI film have excellent stability, enhances the stability and ionic conductivity at the negative electrode-electrolyte interface, significantly reduces the DC internal resistance of the battery, and improves the cycle performance and low-temperature discharge performance of the lithium-ion battery. In addition, lithium salt additives containing oxalic acid groups can also increase the concentration of free lithium ions in the electrolyte, replenishing the lithium ions consumed during the formation of the SEI film, thereby improving the battery's initial capacity and initial charge and discharge efficiency. As a result, the battery has excellent cycle performance, low-temperature discharge performance, and high-temperature storage performance.

[0045] Typically, a battery consists of a positive electrode, a negative electrode, an electrolyte, and a separator. During the battery's charge and discharge processes, active ions are inserted and removed between the positive and negative electrodes. The electrolyte conducts ions between the positive and negative electrodes. The separator, located between the positive and negative electrodes, primarily prevents short circuits between the positive and negative electrodes while allowing ions to pass through.

[0046] The positive electrode sheet includes a positive electrode current collector and a positive electrode active material layer disposed on at least one side of the positive electrode current collector, wherein the positive electrode active material layer includes a positive electrode active material.

[0047] In some embodiments of the present application, the positive electrode current collector may include a metal foil or a composite positive electrode current collector. For example, the metal foil may be aluminum foil. The composite positive electrode current collector may include a polymer material base layer and a metal layer formed on at least one side of the polymer material base layer. For example, the composite negative electrode current collector may be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, etc.) on a polymer material substrate (such as polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), etc.).

[0048] As an example, the positive electrode current collector has two surfaces facing each other in its thickness direction, and the positive electrode active material layer is provided on either or both of the two facing surfaces of the positive electrode current collector.

[0049] In some embodiments of the present application, the positive electrode active material layer may further include a positive electrode active material. The positive electrode active material may be a positive electrode active material for batteries known in the art.

[0050] As an example, the positive electrode active material may include at least one of the following materials: lithium-containing phosphates with an olivine structure, lithium transition metal oxides, and their respective modified compounds. However, the present application is not limited to these materials, and other traditional materials that can be used as positive electrode active materials for batteries may also be used. These positive electrode active materials may be used alone or in combination of two or more. Examples of lithium transition metal oxides may include, but are not limited to, lithium cobalt oxide (such as LiCoO2), lithium nickel oxide (such as LiNiO2), lithium manganese oxide (such as LiMnO2, LiMn2O4), lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide (such as LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (also referred to as NCM 333 ), LiNi 0.5 Co 0.2 Mn 0.3 O2 (also referred to as NCM 523 ), LiNi 0.5 Co 0.25 Mn 0.25 O2 (also referred to as NCM 211 ), LiNi 0.6 Co 0.2 Mn 0.2 O2 (also referred to as NCM 622), LiNi 0.8 Co 0.1 Mn 0.1 O2 (also referred to as NCM 811 ), lithium nickel cobalt aluminum oxide (such as LiNi 0.8 Co 0.15 Al 0.05 O2) or at least one of its modified compounds. Examples of olivine-structured lithium-containing phosphates may include, but are not limited to, at least one of lithium iron phosphate (such as LiFePO4 (also referred to as LFP)), a composite material of lithium iron phosphate and carbon, lithium manganese phosphate (such as LiMnPO4), a composite material of lithium manganese phosphate and carbon, lithium iron manganese phosphate, or a composite material of lithium iron manganese phosphate and carbon.

[0051] In some embodiments of the present application, the positive electrode active material layer may further optionally include a conductive agent. As an example, the conductive agent may include at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0052] In some embodiments of the present application, the positive electrode active material layer may further optionally include a binder. As an example, the binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), a vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, a vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, a tetrafluoroethylene-hexafluoropropylene copolymer, and a fluorine-containing acrylate resin.

[0053] In some embodiments of the present application, the positive electrode sheet can be prepared by the following method: the components for preparing the positive electrode sheet, such as the positive electrode active material, the conductive agent, and the binder, are dispersed in a solvent (such as N-methylpyrrolidone) to form a positive electrode slurry; the positive electrode slurry is coated on the positive electrode collector, and after drying, cold pressing and other processes, the positive electrode sheet can be obtained.

[0054] The negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer disposed on at least one side of the negative electrode current collector, wherein the negative electrode active material layer includes a negative electrode active material.

[0055] In some embodiments of the present application, the negative electrode current collector may be a metal foil or a composite current collector. For example, copper foil may be used as the metal foil. The composite current collector may include a polymer substrate and a metal layer formed on at least one surface of the polymer substrate. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, etc.) on a polymer substrate (such as a substrate made of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), etc.).

[0056] In some embodiments of the present application, the negative electrode active material may be a negative electrode active material for batteries known in the art. For example, the negative electrode active material may include at least one of the following materials: graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, and lithium titanate. The silicon-based material may include at least one of elemental silicon, silicon oxides, silicon-carbon complexes, silicon-nitrogen complexes, and silicon alloys. The tin-based material may include at least one of elemental tin, tin oxides, and tin alloys.

[0057] In some embodiments of the present application, the negative electrode active material layer may further optionally include a binder. The binder may include at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0058] In some embodiments of the present application, the negative electrode active material layer may further include a conductive agent, which may include at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0059] In some embodiments of the present application, the negative electrode active material layer may optionally further include other additives, such as a thickener (eg, sodium carboxymethyl cellulose (CMC-Na)).

[0060] In some embodiments of the present application, the negative electrode sheet can be prepared by the following method: the components for preparing the negative electrode sheet, such as the negative electrode active material, the conductive agent, the binder and any other components, are dispersed in a solvent (such as deionized water) to form a negative electrode slurry; the negative electrode slurry is coated on the negative electrode collector, and after drying, cold pressing and other processes, the negative electrode sheet can be obtained.

[0061] The present application has no particular limitation on the type of isolation membrane, and any known isolation membrane with a porous structure having good chemical stability and mechanical stability can be selected.

[0062] In some embodiments of the present application, the material of the isolation membrane may include at least one of glass fiber, non-woven fabric, polyethylene, polypropylene, or polyvinylidene fluoride.

[0063] It should be noted that the features and advantages described above for the electrolyte are also applicable to the battery and will not be repeated here.

[0064] The following embodiments of the present invention are described in detail. It should be noted that the following embodiments are illustrative and are intended only to explain the present invention and are not to be construed as limiting the present invention. In addition, unless otherwise expressly stated, all reagents used in the following embodiments are commercially available or can be synthesized according to methods described herein or known methods. Reaction conditions not listed are also readily available to those skilled in the art.

[0065] Example 1

[0066] 1. Preparation of positive electrode sheet

[0067] The positive electrode active material LiNi 0.8 Co 0.1 Mn 0.1 O2, conductive carbon black, and binder polyvinylidene fluoride (PVDF) are added to N-methylpyrrolidone (NMP) in a mass ratio of 96.8:2:1.2 to prepare a positive electrode slurry (the solid content in the positive electrode slurry is 68wt%). The positive electrode slurry is coated on the upper and lower surfaces of the aluminum foil and dried and then cold pressed. The positive electrode sheets are then made after trimming, cutting, and striping.

[0068] 2. Preparation of negative electrode sheet

[0069] Graphite, conductive carbon black, thickener carboxymethyl cellulose (CMC), and adhesive styrene-butadiene rubber (SBR) are mixed in deionized water at a mass ratio of 95:1.5:2:1.5 to prepare a negative electrode slurry (the solid content in the negative electrode slurry is 49wt%). The negative electrode slurry is coated on the upper and lower surfaces of copper foil and dried. It is then cold pressed, trimmed, cut into pieces, and slit into strips to make negative electrode sheets.

[0070] 3. Preparation of electrolyte

[0071] In an argon-filled glove box, the compound represented by Formula 1 and a lithium salt additive containing an oxalic acid group were added to an organic solvent. After mixing evenly, LiPF6 was slowly added. After the lithium salt was completely dissolved, an electrolyte with a lithium salt concentration of 1 mol / L was obtained.

[0072] 4. Isolation film

[0073] A 16 μm polyethylene film was used as the separator.

[0074] 5. Lithium-ion battery preparation

[0075] The positive electrode sheet, separator, and negative electrode sheet are stacked in order, with the separator placed between the positive and negative electrode sheets to isolate the positive and negative electrodes. The bare battery cell is wound and the tabs are welded. The bare battery cell is placed in an outer package, and the prepared electrolyte is injected into the dried battery cell. The battery cell is packaged, allowed to stand, formed, and shaped to complete the preparation of the lithium-ion battery.

[0076] The preparation methods of the lithium ion batteries of Examples 2-25 and Comparative Examples 1-4 are the same as those of Example 1, except that the composition and content of the electrolyte additives are different, as shown in Table 1.

[0077] Table 1

[0078] The initial charge and discharge efficiency, room temperature cycle performance, high temperature cycle performance, high temperature storage performance and low temperature discharge performance of the lithium ion batteries obtained in Examples 1-25 and Comparative Examples 1-4 were characterized. The characterization results are shown in Table 2.

[0079] (1) Test method for initial charge and discharge efficiency:

[0080] Charge at 25°C at a constant current of 0.1C for 390 minutes (C1). Let stand for 5 minutes, then charge again at a constant current of 0.1C to 4.4V. Then charge at a constant voltage to a cutoff current of 0.05C (C2). Finally, discharge the battery at a constant current of 0.1C to a cutoff voltage of 3.0V (C3). The initial charge and discharge efficiency = 100% * C3 / (C1 + C2).

[0081] (2) Normal temperature cycle performance test method:

[0082] Charge the battery at 1.0C constant current to 4.4V at 25℃, then charge it at constant voltage to a cutoff current of 0.05C, and then discharge it at 1.0C constant current. The discharge capacity is recorded as C0. Repeat the charge and discharge until the capacity decays to 80% of C0, and record the number of cycles.

[0083] (3) High temperature cycle performance test method:

[0084] Charge the battery at 45°C at a constant current of 1.0C to 4.4V, then charge it at a constant voltage to a cutoff current of 0.05C, and then discharge it at a constant current of 1.0C. The discharge capacity is recorded as C0. Repeat the charge and discharge until the capacity decays to 80% of C0, and record the number of cycles.

[0085] (4) High temperature storage performance test method:

[0086] At 25°C, charge at a constant current of 1.0C to 4.4V, charge at a constant voltage of 4.4V to a cutoff current of 0.05C, and then discharge the battery at a constant current of 0.5C. The discharge capacity is recorded as C1. Remove the battery and use a thickness tester to measure its initial thickness, which is T1. At 25°C, charge at a constant current of 1.0C to 4.4V, charge at a constant voltage of 4.4V to a cutoff current of 0.05C, and then transfer the battery to 60°C and let it sit for 15 days. Use a thickness tester to measure its thickness after 15 days, which is T2. Then discharge the battery at a constant current of 1.0C, and record the discharge capacity as C2. After 15 days of storage at 60°C, the capacity retention rate = C2 / C1*100%, and the battery expansion rate = 100%*(T2-T1) / T1.

[0087] (5) Low temperature discharge performance test method:

[0088] At 25°C, charge the battery at a constant current of 1.0C to 4.4V, charge it at a constant voltage of 4.4V to a cutoff current of 0.05C, and then discharge it at a constant current of 0.5C. The discharge capacity is recorded as C4. At -20°C, let it sit for 4 hours, then discharge it at a constant current of 0.5C. The discharge capacity is recorded as C5. The -20°C low-temperature discharge capacity retention rate = C5 / C4*100%.

[0089] Table 2

[0090] It can be seen from the data in Table 2 that, by comparing Examples 1-25 with Comparative Example 1, the room temperature cycle performance, high temperature cycle performance, high temperature storage capacity retention rate, high temperature storage battery expansion rate, and low temperature discharge capacity retention rate of the batteries of Examples 1-25 are significantly better than the above performances of the battery of Comparative Example 1, indicating that the use of the electrolyte additive of the present application can improve the cycle performance, low temperature discharge performance, and high temperature storage performance of lithium batteries.

[0091] Comparing Examples 1-25 and Comparative Example 2, the first discharge efficiency of the batteries of Examples 1-25 is higher than that of Comparative Example 2, indicating that the addition of lithium salt additives containing oxalic acid groups can replenish the lithium ions consumed during the formation of the SEI film, thereby improving the initial capacity and first charge and discharge efficiency of the battery.

[0092] Comparing Example 2 with Comparative Example 2 and Comparative Example 3, the electrolyte additive of Comparative Example 2 only contains the compound represented by Formula 1, and the overall comprehensive performance of its battery is worse than that of Example 2. The electrolyte additive of Comparative Example 3 only contains the lithium salt additive containing an oxalic acid group. Although its battery's first discharge efficiency and low-temperature discharge capacity retention rate are comparable to those of Example 2, other battery cycle performance, high-temperature storage capacity retention rate, and high-temperature storage battery expansion rate are significantly worse than those of Example 2. The electrolyte additive of Example 2 includes both the compound represented by Formula 1 and the lithium salt additive containing an oxalic acid group. Compared with Comparative Examples 2 and 3, the overall performance of the battery of Example 2 is significantly improved, indicating that the compound represented by Formula 1 and the lithium salt additive containing an oxalic acid group of the present application work synergistically with each other, thereby significantly improving the comprehensive performance of the battery.

[0093] Comparing Examples 1-5 and Comparative Example 4, Comparative Example 4 uses other sulfate ester electrolyte additives. The first discharge efficiency, cycle performance, high-temperature storage capacity retention rate and low-temperature discharge capacity retention rate of the batteries of Examples 1-5 are all higher than those of Comparative Example 4. In particular, the high-temperature storage battery expansion rate of the batteries of Examples 1-5 is significantly lower than that of Comparative Example 4, indicating that the use of the electrolyte additives of the present application can significantly improve the initial capacity, cycle performance, low-temperature discharge performance and high-temperature storage performance of the battery.

[0094] In the description of this specification, the reference terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" mean that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art can combine and combine different embodiments or examples described in this specification and features of different embodiments or examples without contradiction.

[0095] Although the embodiments of the present invention have been shown and described above, it will be understood that the above embodiments are illustrative and are not to be construed as limitations on the present invention. A person skilled in the art may change, modify, replace and modify the above embodiments within the scope of the present invention.

Claims

1. An electrolyte additive, wherein: It comprises a compound represented by formula 1 and a lithium salt additive containing an oxalic acid group, 2. The electrolyte additive according to claim 1, wherein The mass ratio of the compound represented by Formula 1 to the lithium salt additive containing an oxalic acid group is 1:(0.5-2.6).

3. The electrolyte additive according to claim 2, wherein The lithium salt additive containing an oxalic acid group includes at least one of a lithium oxalate phosphate additive and a lithium oxalate borate additive.

4. The electrolyte additive according to claim 3, wherein The lithium oxalate phosphate salt additive includes at least one of lithium trioxalate phosphate, lithium difluorobisoxalate phosphate and lithium tetrafluorooxalate phosphate.

5. The electrolyte additive according to claim 4, wherein The mass ratio of the compound represented by formula 1 to the lithium oxalate phosphate additive is 1:(0.5-2.6).

6. The electrolyte additive according to claim 3, wherein The lithium oxalate borate salt additive includes at least one of lithium bis(oxalate borate) and lithium difluoro(oxalate borate).

7. The electrolyte additive according to claim 6, wherein The mass ratio of the compound represented by Formula 1 to the lithium oxalate borate salt additive is 1:(0.8-1.3).

8. An electrolyte, wherein The electrolyte additive comprises the electrolyte additive described in any one of claims 1 to 7.

9. The electrolyte according to claim 8, wherein Based on the total mass of the electrolyte, the mass proportion of the compound represented by Formula 1 is 0.1% to 2%.

10. The electrolyte according to claim 8, wherein Based on the total mass of the electrolyte, the mass proportion of the lithium salt additive containing oxalic acid groups is 0.1% to 2%.

11. The electrolyte according to claim 8, wherein The electrolyte further includes a solvent, and the solvent includes ethylene carbonate.

12. The electrolyte according to claim 11, wherein The mass proportion of the ethylene carbonate in the electrolyte is 25% to 30%.

13. A battery, wherein: The invention comprises the electrolyte according to any one of claims 8 to 12.

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