Battery and preparation method therefor, and electric device

Abstract

Disclosed in the present application are a battery and a preparation method therefor, and an electric device. The battery comprises a positive electrode sheet, a negative electrode sheet and an electrolyte, wherein the mass proportion of water is 50 ppm to 300 ppm based on the total mass of the positive electrode sheet, and the mass proportion of water is 30 ppm to 200 ppm based on the total mass of the negative electrode sheet; the electrolyte comprises a first lithium salt, the first lithium salt comprising LiN(SO2R)2, where R comprises at least one of F or F-substituted hydrocarbyl having 1-3 carbon atoms; and the mass proportion of the first lithium salt is 3% to 10% based on the total mass of the electrolyte. The battery of the present application has long cycle life.

Description

Battery and its preparation method, and power-using device

[0001] Priority information

[0002] This application claims priority and benefits of patent application 202410407325.5 filed with the State Intellectual Property Office of China on April 3, 2024, and incorporates the entire text of it herein by reference. Technical Field

[0003] The present application belongs to the field of batteries, and specifically relates to a battery and an electrical device. Background Art

[0004] Secondary batteries are widely used in energy storage systems such as hydropower, thermal, wind, and solar power plants, as well as in power tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, aerospace, and other fields. As battery applications expand, the performance requirements for secondary batteries are becoming increasingly stringent, and existing secondary batteries have a short cycle life. Summary of the Invention

[0005] In view of the technical problems existing in the background technology, the present application provides a battery, aiming to improve the cycle life of the secondary battery.

[0006] To achieve the above objectives, the first aspect of the present application provides a battery comprising a positive electrode sheet, a negative electrode sheet, and an electrolyte, wherein the mass proportion of water is 50ppm-300ppm based on the total mass of the positive electrode sheet, and the mass proportion of water is 30ppm-200ppm based on the total mass of the negative electrode sheet; the electrolyte comprises a first lithium salt, wherein the first lithium salt comprises: LiN(SO2R)2,

[0007] Wherein, R includes at least one of F or a hydrocarbon group of 1 to 3 carbon atoms substituted by F, and based on the total mass of the electrolyte, the mass proportion of the first lithium salt is 3% to 10%.

[0008] The present application includes at least the following beneficial effects: in the battery of the present application, controlling the mass proportion of water in the positive electrode sheet and the negative electrode sheet, adding a first lithium salt to the electrolyte and controlling its content can significantly reduce the water content in the electrolyte, thereby reducing the damage caused by the generation of HF in the electrolyte to the positive and negative electrodes of the battery, and improving the cycle life of the battery.

[0009] In some embodiments, the mass proportion of water is 100 ppm to 300 ppm based on the total mass of the positive electrode sheet, thereby significantly improving the cycle life of the battery.

[0010] In some embodiments, the mass proportion of water is 100 ppm to 250 ppm based on the total mass of the positive electrode sheet, thereby significantly improving the cycle life of the battery.

[0011] In some embodiments, the mass proportion of water is 50 ppm to 200 ppm based on the total mass of the negative electrode plate, thereby significantly improving the cycle life of the battery.

[0012] In some embodiments, the mass proportion of water is 50 ppm to 150 ppm based on the total mass of the negative electrode plate, thereby significantly improving the cycle life of the battery.

[0013] In some embodiments, the mass proportion of water is 50 ppm to 250 ppm based on the total mass of the positive electrode sheet, thereby significantly improving the cycle life of the battery.

[0014] In some embodiments, the mass proportion of water is 50 ppm to 220 ppm based on the total mass of the positive electrode sheet, thereby significantly improving the cycle life of the battery.

[0015] In some embodiments, the mass proportion of water is 30 ppm to 150 ppm based on the total mass of the negative electrode plate, thereby significantly improving the cycle life of the battery.

[0016] In some embodiments, the mass proportion of water is 30 ppm to 110 ppm based on the total mass of the negative electrode plate, thereby significantly improving the cycle life of the battery.

[0017] In some embodiments, the first lithium salt includes at least one of lithium bis(fluorosulfonyl)imide and lithium bis(trifluoromethanesulfonyl)imide, thereby improving the cycle life of the battery.

[0018] In some embodiments, the positive electrode sheet includes a positive electrode active material, and the positive electrode active material includes LiMn x Fe 1-x-y M y PO4, wherein 0≤x≤1, 0≤y≤0.04, and M comprises at least one of Ti, Mg, Ta, Sc, Cr, Y, Zr, Nb, Mo, La, Ta, W, Hf, V, Ni, Rh, or Os. This can improve the cycle life of the battery.

[0019] In some embodiments, the BET specific surface area of ​​the positive electrode active material is 10 m 2 / g-15m 2 / g. Thus, the cycle life of the battery can be improved.

[0020] In some embodiments, the positive electrode active material further comprises a LiMn x Fe 1-x-y M y A coating material covering at least a portion of the surface of PO 4 , wherein the coating material comprises carbon.

[0021] In some embodiments, the coating material accounts for 0.8% to 3.5% of the total mass of the positive electrode active material, thereby improving the cycle life of the battery.

[0022] In some embodiments, the coating material accounts for 1.3% to 2.5% of the total mass of the positive electrode active material, thereby improving the cycle life of the battery.

[0023] In some embodiments, the negative electrode plate includes a negative electrode active material, and the negative electrode active material includes a silicon-based material, thereby improving the cycle life of the battery.

[0024] In some embodiments, the volume average particle size Dv50 of the silicon-based material is less than or equal to 6 μm, thereby improving the cycle life of the battery.

[0025] In some embodiments, the volume average particle size Dv50 of the silicon-based material is 3 μm to 6 μm, thereby improving the cycle life of the battery.

[0026] In some embodiments, the silicon-based material accounts for 1% to 5% of the total mass of the electrolyte and the total mass of the negative electrode active material, thereby improving the cycle life of the battery.

[0027] In some embodiments, the negative electrode active material further includes a second negative electrode active material, wherein the second negative electrode active material includes at least one of artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, or lithium titanate. This can improve the cycle life of the battery.

[0028] In some embodiments, the volume average particle size Dv50 of the second negative electrode active material is 15 μm to 20 μm, thereby improving the cycle life of the battery.

[0029] In some embodiments, the porosity of the negative electrode plate is 15%-25%, thereby improving the cycle life of the battery.

[0030] In some embodiments, the electrolyte further includes a second lithium salt, wherein the second lithium salt includes at least one of LiPF6, lithium difluorooxalatoborate, lithium dioxalatoborate, or LiClO4. This can improve the cycle life of the battery.

[0031] In some embodiments, the electrolyte further comprises an additive, wherein the additive comprises at least one of LiPO2F2 or LiSO3F, thereby improving the cycle life of the battery.

[0032] In some embodiments, one or more of the following conditions are met:

[0033] Based on the total mass of the electrolyte, the mass proportion of the LiPO2F2 is 0.1%-0.5%;

[0034] Based on the total mass of the electrolyte, the mass proportion of the LiSO3F is 0.1%-0.5%, thereby improving the cycle life of the battery.

[0035] In some embodiments, one or more of the following conditions are met:

[0036] Wherein, based on the total mass of the electrolyte, the mass proportion of the LiPO2F2 is less than or equal to 0.2%;

[0037] Based on the total mass of the electrolyte, the mass proportion of the LiSO3F is less than or equal to 0.1%, thereby improving the cycle life of the battery.

[0038] Based on the total mass of the electrolyte, the mass proportion of the first lithium salt is 5%-10%.

[0039] In a second aspect of the present application, the present application provides a method for preparing the battery according to the first aspect, comprising:

[0040] Assembling the positive electrode sheet and the negative electrode sheet into a bare cell, injecting electrolyte to obtain a battery;

[0041] Wherein, based on the total mass of the positive electrode plate, the mass proportion of water is 50ppm-300ppm, based on the total mass of the negative electrode plate, the mass proportion of water is 30ppm-200ppm; the electrolyte includes a first lithium salt, and the first lithium salt includes: LiN(SO2R)2,

[0042] Wherein, R includes at least one of F or a hydrocarbon group of 1 to 3 carbon atoms substituted by F, and based on the total mass of the electrolyte, the mass proportion of the first lithium salt is 3% to 10%.

[0043] Therefore, the battery prepared in the present application controls the mass proportion of water in the positive electrode sheet and the negative electrode sheet, adds the first lithium salt to the electrolyte and controls its content, which can significantly reduce the water content in the electrolyte and improve the cycle life of the battery.

[0044] In some embodiments, before injecting the electrolyte, the process further includes drying the bare cell, thereby increasing the cycle life of the battery.

[0045] In some embodiments, the drying temperature is 100° C.-120° C. This can improve the cycle life of the battery.

[0046] In some embodiments, the drying time is 10 hours to 20 hours, thereby increasing the cycle life of the battery.

[0047] In some embodiments, after injecting the electrolyte, the process further includes forming the battery, thereby increasing the cycle life of the battery.

[0048] In the third aspect of the present application, the present application proposes an electrical device, comprising the battery described in the first aspect of the present application or the battery prepared by the method described in the second aspect.

[0049] Additional aspects and advantages of the present application will be given in part in the description below, and in part will become obvious from the description below, or will be learned through practice of the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0050] Various other advantages and benefits will become apparent to those skilled in the art upon reading the detailed description of the preferred embodiment below. The accompanying drawings are for illustration purposes only and are not to be considered as limiting the present application. The same reference numerals are used throughout the drawings to represent the same components. In the drawings:

[0051] FIG1 is a schematic diagram of a battery according to one embodiment of the present application.

[0052] FIG. 2 is an exploded view of the battery according to one embodiment of the present application shown in FIG. 1 .

[0053] FIG3 is a schematic diagram of a battery module according to an embodiment of the present application.

[0054] FIG4 is a schematic diagram of a battery pack according to an embodiment of the present application.

[0055] FIG. 5 is an exploded view of the battery pack shown in FIG. 4 according to an embodiment of the present application.

[0056] FIG6 is a schematic diagram of an electrical device using a battery as a power source according to an embodiment of the present application.

[0057] Explanation of reference numerals: 1 battery cell; 11 housing; 12 electrode assembly; 13 cover plate; 2 battery module; 3 battery pack; 31 upper case; 32 lower case. DETAILED DESCRIPTION

[0058] The following embodiments of the technical solution of the present application are described in detail. The following embodiments are only used to more clearly illustrate the technical solution of the present application and are therefore only used as examples and are not intended to limit the scope of protection of the present application.

[0059] References herein to "embodiments" mean that a particular feature, structure, or characteristic described in connection with the embodiments may be included in at least one embodiment of the present application. The appearance of this phrase in various places in the specification does not necessarily refer to the same embodiment, nor does it constitute an independent or alternative embodiment that is mutually exclusive of other embodiments. It is understood, both explicitly and implicitly, by those skilled in the art that the embodiments described herein may be combined with other embodiments.

[0060] The "ranges" disclosed herein are defined in terms of lower and upper limits. A given range is defined by selecting a lower limit and an upper limit, and the selected lower and upper limits define the boundaries of a particular range. For example, if ranges of 60-120 and 80-110 are listed for a particular parameter, it is understood that ranges of 60-110 and 80-120 are also contemplated. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are listed, the following ranges are all contemplated: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In this application, unless otherwise indicated, the numerical range "ab" represents an abbreviation for any combination of real numbers between a and b, where a and b are both real numbers. For example, the numerical range "0-5" represents that all real numbers between "0-5" have been listed herein, and "0-5" is simply an abbreviation for these numerical combinations. In addition, when a parameter is expressed as an integer ≥ 2, it is equivalent to disclosing that the parameter is, for example, an integer of 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0061] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0062] Unless otherwise specified, all technical features and optional technical features of this application can be combined with each other to form a new technical solution.

[0063] Unless otherwise specified, all steps of the present application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or may include steps (b) and (a) performed sequentially. For example, the method may further include step (c), indicating that step (c) may be added to the method in any order, for example, the method may include steps (a), (b) and (c), or may include steps (a), (c) and (b), or may include steps (c), (a) and (b), etc.

[0064] Currently, judging by market developments, the application of secondary batteries is becoming increasingly widespread. They are not only used in energy storage systems such as hydropower, thermal power, wind power, and solar power stations, but are also widely used in electric vehicles such as electric bicycles, electric motorcycles, and electric vehicles, as well as in military equipment and aerospace, among other fields.

[0065] In secondary batteries, the electrolyte is generally a non-aqueous electrolyte. The presence of trace amounts of water in the electrolyte is beneficial to the formation of the SEI film of lithium-ion batteries and the improvement of battery performance. However, when the electrolyte contains excessive water, the excess water may react with the lithium salt (such as LiPF6) in the electrolyte to generate HF or even phosphoric acid, resulting in the loss of lithium salts. The generated acid will also corrode the positive and negative electrodes, causing the battery life to decay. In addition, after the battery is prepared, water in the positive electrode, negative electrode, isolation membrane, etc. may also enter the electrolyte, causing the water content in the electrolyte to increase, resulting in a decrease in the battery cycle life.

[0066] In the present application, the first lithium salt in the electrolyte is relatively stable and does not react easily with water. It can reduce the generation of HF or even acids such as phosphoric acid in the electrolyte, reduce the loss of the first lithium salt, and reduce the corrosion of the generated acid on the positive electrode and negative electrode sheets, thereby improving the life of the battery. However, the first lithium salt has a strong polarity and easily absorbs water, making it easier for water in the positive electrode and negative electrode sheets to enter the electrolyte, resulting in excessive water in the electrolyte, which will cause the battery life to be shortened. Therefore, the content of the first lithium salt in the electrolyte is controlled within the range of 3%-10%, and the water content in the positive electrode sheet is correspondingly controlled within the range of 50ppm-300ppm, and the water content in the negative electrode sheet is correspondingly controlled within the range of 30ppm-200ppm. On the one hand, the first lithium salt can absorb part of the water in the positive electrode sheet and the negative electrode sheet into the electrolyte, and this part of water is helpful for the formation of the battery SEI film and the improvement of the battery cycle performance; on the other hand, it prevents too much water from entering the electrolyte from the positive electrode sheet and the negative electrode sheet, and due to the stability of the first lithium salt itself, the stability of the electrolyte can be improved, which can further improve the cycle life of the battery.

[0067] The battery disclosed in the embodiment of the present application includes a lithium-ion battery, and the battery disclosed in the embodiment of the present application can be used in electrical devices that use the battery as a power source or various energy storage systems that use the battery as an energy storage element. Electrical devices may include but are not limited to mobile phones, tablets, laptops, electric toys, power tools, battery cars, electric cars, ships, spacecraft, etc. Among them, electric toys may include fixed or mobile electric toys, for example, game consoles, electric car toys, electric ship toys and electric airplane toys, etc., and spacecraft may include airplanes, rockets, space shuttles and spacecraft, etc.

[0068] In a first aspect, the present application provides a battery comprising a positive electrode sheet, a negative electrode sheet, and an electrolyte. Based on the total mass of the positive electrode sheet, the mass proportion of water is 50ppm-300ppm, and based on the total mass of the negative electrode sheet, the mass proportion of water is 30ppm-200ppm; the electrolyte comprises a first lithium salt, and the first lithium salt comprises: LiN(SO2R)2,

[0069] Wherein, R includes at least one of F or a hydrocarbon group of 1 to 3 carbon atoms substituted by F, and based on the total mass of the electrolyte, the mass proportion of the first lithium salt is 3% to 10%.

[0070] As an example, when R includes a hydrocarbon group of 1-3 carbon atoms substituted with F, the number of carbon atoms in the hydrocarbon group can be 1-3, 1-2, 2-3, etc.

[0071] In the battery of the present application, the first lithium salt in the electrolyte is relatively stable and does not react easily with water. This can reduce the generation of acids such as HF and even phosphoric acid in the electrolyte, reduce the loss of the first lithium salt, and reduce the corrosion of the generated acid on the positive and negative electrode sheets, thereby improving the life of the battery. However, the first lithium salt has a strong polarity and easily absorbs water, making it easier for water in the positive and negative electrode sheets to enter the electrolyte, resulting in excessive water in the electrolyte, which in turn causes the battery life to be shortened. Therefore, the content of the first lithium salt in the electrolyte is controlled within the range of 3%-10%, and the water content in the positive electrode sheet is correspondingly controlled within the range of 50ppm-300ppm, and the water content in the negative electrode sheet is correspondingly controlled within the range of 30ppm-200ppm. On the one hand, the first lithium salt can absorb a portion of the water in the positive electrode sheet and the negative electrode sheet into the electrolyte in an appropriate amount. This water is helpful for the formation of the battery SEI film and the improvement of the battery cycle performance; on the other hand, it prevents too much water from entering the electrolyte from the positive electrode sheet and the negative electrode sheet, and due to the stability of the first lithium salt itself, the stability of the electrolyte can be improved, which can further improve the cycle life of the battery. In summary, the battery proposed in this application has an excellent cycle life.

[0072] In some embodiments of the present application, based on the total mass of the electrolyte, the mass proportion of the first lithium salt is 3%-10%. For example, based on the total mass of the electrolyte, the mass proportion of the first lithium salt can be 3%-9.9%, 5.5%-9.5%, 6%-9%, 6.5%-8.5%, 7%-8%, etc. The mass proportion of the first lithium salt in the electrolyte is controlled within the above range. On the one hand, the first lithium salt can absorb a portion of the water in the positive electrode sheet and the negative electrode sheet into the electrolyte in an appropriate amount. This part of water has a great effect on the formation and It helps to improve the battery cycle performance; on the other hand, the first lithium salt has a strong polarity. Controlling the content of the first lithium salt within the above range can reduce the excessive absorption of water in the positive electrode sheet and the negative electrode sheet into the electrolyte due to excessive first lithium salt, so that the water entering the electrolyte from the positive electrode sheet and the negative electrode sheet will not be too much. It can also reduce the lack of water in the electrolyte caused by too little first lithium salt, which is not conducive to the formation of the battery SEI film and the improvement of the battery cycle performance. Moreover, due to the stability of the first lithium salt itself, the stability of the electrolyte can be improved, which can further improve the cycle life of the battery.

[0073] In other embodiments of the present application, based on the total mass of the electrolyte, the mass proportion of the first lithium salt is 5%-10%. It is understood that the first lithium salt will be consumed during the battery formation process (for example, participating in the formation of SEI). Therefore, 5%-10% can be understood as the content of the first lithium salt in the battery electrolyte before formation. After formation, its content may be slightly reduced. For example, before formation, the mass proportion of the first lithium salt in the electrolyte is 5%, and after formation, the mass proportion of the first lithium salt in the electrolyte becomes 3%. Regardless of whether the battery has been formed or not, as long as the content of the first lithium salt in its electrolyte (3%-10%) meets the requirements of the claims of this application, it falls within the scope of protection of this application.

[0074] It is understood that “the mass proportion of the first lithium salt based on the total mass of the electrolyte” is a well-known definition in the art and can be measured by methods well-known in the art. For example, it can be measured by the following method:

[0075] The battery was disassembled and the electrolyte was taken out. Referring to the standard JY / T020-1996 "General Rules for Ion Chromatography Analysis Methods", the mass proportion of the first lithium salt in the electrolyte was determined using an ion chromatograph (model Thermo Nicolet IS10).

[0076] In some embodiments of the present application, the mass percentage of water based on the total mass of the positive electrode plate is 50ppm-300ppm. For example, based on the total mass of the electrolyte and the total mass of the positive electrode plate, the mass percentage of water can be 50ppm-299ppm, 110ppm-290ppm, 120ppm-280ppm, 130ppm-270ppm, 140ppm-260ppm, 150ppm-250ppm, 160ppm-240ppm, 170ppm-230ppm, 180ppm-220ppm, 190ppm-210ppm, etc. By controlling the water content in the positive electrode plate within the above range, the first lithium salt can appropriately absorb a portion of the water in the positive electrode plate into the electrolyte. This water contributes to the formation of the SEI film of the battery and improves the cycle performance of the battery. Furthermore, the amount of water entering the electrolyte from the positive electrode plate is prevented from being excessive, thereby improving the stability of the electrolyte and further increasing the cycle life of the battery.

[0077] In other embodiments of the present application, based on the total mass of the positive electrode plate, the mass proportion of water is 100ppm-300ppm. For example, based on the total mass of the positive electrode plate, the mass proportion of water is 100ppm-250ppm. At this time, the secondary battery can be a battery that has not been formed, that is, before formation, and the water content of its positive electrode plate is slightly higher than the water content of the positive electrode plate of the formed battery. For example, before formation, the mass proportion of water in the positive electrode plate is 100ppm-300ppm, and the mass proportion of water in the positive electrode plate after formation is 50ppm-250ppm, which can improve the stability of the electrolyte and further improve the cycle life of the battery.

[0078] It can be understood that the battery preparation process includes assembling the positive electrode plate, the negative electrode plate, the isolation membrane, etc. into a bare battery cell, drying, and then injecting the electrolyte. It also goes through the processes of packaging, standing, forming, and shaping to form a battery cell. When the water content of the electrode (positive electrode plate, negative electrode plate) is limited to the water content before formation, it refers to the water content of the electrode after drying and before injecting the electrolyte.

[0079] In other embodiments of the present application, based on the total mass of the positive electrode plate, the mass proportion of water is 50ppm-250ppm. For example, based on the total mass of the positive electrode plate, the mass proportion of water is 50ppm-220ppm. At this time, the secondary battery can be a battery after formation. Since a portion of the water in the plate enters the electrolyte after formation, the water content of the positive electrode plate is slightly lower than that of the positive electrode plate of the battery that has not been formed, which can improve the stability of the electrolyte and further improve the cycle life of the battery.

[0080] It can be understood that when the water content of the positive electrode sheet and the negative electrode sheet is determined, if the first lithium salt is too much, more water will enter the electrolyte, and too much water will be detrimental to the cycle performance of the battery; if the first lithium salt is too little, less water will enter the electrolyte, and too little water will also affect the formation of the battery SEI film and the improvement of battery performance; similarly, when the content of the first lithium salt in the electrolyte is determined, if the water content in the positive electrode sheet and the negative electrode sheet is too much, more water will enter the electrolyte, and if the water content in the positive electrode sheet and the negative electrode sheet is too little, less water will enter the electrolyte; therefore, the embodiment of the present application simultaneously controls the water content of the positive electrode sheet (50ppm-300ppm), the water content of the negative electrode sheet (30ppm-200ppm) and the content of the first lithium salt (3%-10% by mass in the electrolyte) to optimize the amount of water entering the electrolyte, neither too much nor too little, thereby achieving the optimal battery cycle life.

[0081] It can be understood that “the mass proportion of water based on the total mass of the positive electrode sheet” can be interpreted as the average number of micrograms of water contained in each gram of the positive electrode sheet. For example, based on the total mass of the positive electrode sheet, the mass proportion of water is 100 ppm, which means that on average 1 gram of the positive electrode sheet contains 100 μg of water. “The mass proportion of water based on the total mass of the positive electrode sheet” can be measured by methods known in the art, for example, it can be measured by the following method:

[0082] Referring to the standard GB / T 6283-2008, the battery is disassembled to obtain the positive electrode sheet, which is then crushed and measured using the Karl Fischer method (direct coulometric titration). This is a very sensitive chemical analysis method suitable for the determination of trace moisture. In short, the method includes:

[0083] Electrode water content test method:

[0084] 1. With the battery fully discharged, perform the following operations in an environment with a humidity of less than 2°C:

[0085] 2. Disassemble the battery, remove the positive electrode, and soak it in DMC (dimethyl carbonate) for more than 2 hours;

[0086] 3. Pour out the DMC and let the electrode air dry naturally;

[0087] 4. Take several electrodes, record the electrode mass m1, and test it using the following instrument: Fully automatic water content tester (model: Swiss Metrohm 874+831). Enter m1 in the instrument and the instrument will automatically output the electrode water content.

[0088] It can be understood that, in the examples of the present application, 1 ppm = 1 μg / g.

[0089] In some embodiments of the present application, the mass percentage of water based on the total mass of the negative electrode plate is 30ppm-200ppm. For example, the mass percentage of water based on the total mass of the negative electrode plate can be 30ppm-199ppm, 60ppm-190ppm, 70ppm-180ppm, 80ppm-170ppm, 90ppm-160ppm, 100ppm-150ppm, 110ppm-140ppm, 120ppm-130ppm, etc. Specifically, by controlling the water content in the negative electrode plate within the above range, the first lithium salt can appropriately absorb a portion of the water in the negative electrode plate into the electrolyte. This water contributes to the formation of the battery SEI film and the improvement of the battery cycle performance. Furthermore, the water content in the negative electrode plate is prevented from entering the electrolyte in excess, thereby improving the stability of the electrolyte and further increasing the cycle life of the battery.

[0090] In other embodiments of the present application, based on the total mass of the negative electrode plate, the mass proportion of water is 50ppm-200ppm. For example, based on the total mass of the negative electrode plate, the mass proportion of water is 50ppm-150ppm. At this time, the secondary battery can be a battery that has not been formed, that is, before formation, and the water content of its negative electrode plate is slightly higher than the water content of the negative electrode plate of a battery that has been formed. For example, before formation, the mass proportion of water in the negative electrode plate is 50ppm-200ppm, and after formation, the mass proportion of water in the negative electrode plate is 30ppm-150ppm, which can improve the stability of the electrolyte and further improve the cycle life of the battery.

[0091] In other embodiments of the present application, the mass percentage of water is 30ppm-150ppm based on the total mass of the negative electrode plate. For example, the mass percentage of water is 30ppm-110ppm based on the total mass of the negative electrode plate. In this case, the secondary battery can be a battery that has undergone formation, and the water content of its negative electrode plate is slightly lower than that of the negative electrode plate of a battery that has not undergone formation, which can improve the stability of the electrolyte and further increase the cycle life of the battery.

[0092] It is understood that “the mass proportion of water based on the total mass of the negative electrode sheet” is a well-known definition in the art and can be measured by methods well-known in the art. For example, it can be measured by the following method:

[0093] Referring to the standard GB / T 6283-2008, the battery was disassembled to obtain the negative electrode sheet, which was then crushed and measured using the Karl Fischer method (direct coulometric titration). This method is basically the same as the previous method for testing the moisture content of the positive electrode sheet and will not be repeated here.

[0094] Based on the total mass of the negative electrode plate and the mass proportion of water, the detailed testing method is the same as that of the positive electrode plate and will not be repeated here.

[0095] It is understood that after the battery is formed, some of the water in the positive and negative electrode sheets enters the electrolyte and is consumed. Therefore, after the battery is formed, the water content in the positive and negative electrode sheets decreases compared to before formation. Regardless of whether the battery has been formed or not, and regardless of whether the battery has not been cycled after formation or after any number of cycles, as long as the water content of the positive electrode sheet (50ppm-300ppm), the water content of the negative electrode sheet (30ppm-200ppm), and the content of the first lithium salt in the electrolyte (3%-10%) meet the limitations of the claims of this application, they all fall within the scope of protection of this application. The limitations of other contents below are similar and will not be repeated here.

[0096] In some embodiments of the present application, the first lithium salt includes at least one of lithium bis(fluorosulfonyl)imide (LiFSI) and lithium bis(trifluoromethanesulfonyl)imide (CAS No. 90076-65-6). Specifically, the first lithium salt is relatively stable in the electrolyte and does not readily react with water. It can absorb a moderate amount of the water in the positive electrode into the electrolyte, which helps form the SEI film and improve the battery's cycle performance. Furthermore, it prevents excessive water from entering the electrolyte from the positive electrode. Furthermore, due to the inherent stability of the first lithium salt, the stability of the electrolyte can be improved, further extending the battery's cycle life.

[0097] In some embodiments of the present application, the positive electrode sheet includes a positive electrode active material, and the positive electrode active material includes LiMn x Fe 1-x-y M yPO4, wherein 0≤x≤1, 0≤y≤0.04, M includes at least one of Ti, Mg, Ta, Sc, Cr, Y, Zr, Nb, Mo, La, Ta, W, Hf, V, Ni, Rh or Os, for example, 0≤x≤0.99, 0.1≤x≤0.9, 0.2≤x≤0.8, 0.3≤x≤0.7, 0.4≤x≤0.5, etc., 0≤y≤0.03, 0.01≤y≤0.02, etc. Specifically, the above-mentioned positive electrode active material is a lithium iron phosphate positive electrode active material, and the lithium iron phosphate positive electrode active material is a lithium iron phosphate positive electrode active material. The moisture in the active material includes bound water and adsorbed water. Due to its own structure, the bound water is difficult to dry. The water content in the positive electrode plate is controlled in the range of 50ppm-300ppm. The moisture in lithium iron phosphate positive active materials is basically bound water. The first lithium salt can absorb a portion of the above-mentioned bound water in the positive electrode plate into the electrolyte in an appropriate amount, thereby improving the cycle life of the battery. In addition, the electrochemical properties of lithium iron phosphate positive active materials themselves are relatively stable, with a stable charge and discharge platform, which can further improve the cycle life of the battery.

[0098] On the other hand, the LiMn x Fe 1-x-y M y The water content in the positive and negative electrodes of PO4 is controlled within the above range. When multiple batteries are assembled into a battery module or battery pack, the difference in water content among the batteries in the battery module or battery pack can be made smaller, that is, the water content in each battery has good consistency, thereby reducing the poor long-term cycle life of the battery module or battery pack caused by poor consistency and improving the cycle life of the entire battery module or battery pack.

[0099] In some embodiments of the present application, the positive electrode active material further comprises a LiMn x Fe 1-x-y M y A coating material is provided on at least a portion of the surface of the PO4, wherein the coating material includes carbon. The presence of the carbon coating material may affect the water content of the positive electrode sheet. Furthermore, providing the coating material on the surface of the lithium iron phosphate positive electrode active material can improve the electronic conductivity of the positive electrode active material and thus increase the cycle life of the battery.

[0100] In some embodiments of the present application, based on the total mass of the positive electrode active material, the mass proportion of the coating material is 0.8%-3.5%. For example, it can be 0.8%-3.4%, 1%-3%, 1.5%-2.5%, etc. Controlling the mass proportion of the coating material within the above range may be beneficial to control the water content of the positive electrode sheet within the required range, and can reduce the insufficient conductivity of the positive electrode active material caused by too low a coating material content, and reduce the excessive thickness of the coating material caused by too high a coating material content, and the ion transmission path is too long, further improving the cycle life of the battery. In other embodiments of the present application, based on the total mass of the positive electrode active material, the mass proportion of the coating material is 1.3%-2.5%.

[0101] In some embodiments of the present application, the BET specific surface area of ​​the positive electrode active material is 10 m 2 / g-15m 2 / g. For example, the BET specific surface area of ​​the positive electrode active material can be 10m 2 / g-14.9m 2 / g,11m 2 / g-14m 2 / g,12m 2 / g-13m 2 / g, etc., thereby controlling the BET specific surface area of ​​the positive electrode active material within the above range, making it easier to dry the water in the obtained positive electrode plate, and reducing the problem of the positive electrode plate easily absorbing water caused by an excessively large BET specific surface area, while reducing the problem of the water in the negative electrode plate being difficult to dry caused by an excessively small BET specific surface area, thereby improving the cycle life of the battery.

[0102] It is understood that the “BET specific surface area of ​​the positive electrode active material” is a well-known definition in the art and can be measured by methods well-known in the art. For example, it can be measured by the following method:

[0103] After the positive electrode active material is powdered, the specific surface area is determined using a surface area meter-static capacity method according to the reference standard GB / T19587-2017. Specifically, according to the embodiments of the present application, a flow method gas adsorption type specific surface area measuring device (model AUY220) can be used for measurement.

[0104] In some embodiments of the present application, the negative electrode plate includes a negative electrode active material, and the negative electrode active material includes a silicon-based material. Specifically, because silicon-based materials have many hydroxyl groups on their surfaces, they are sensitive to water or HF generated by water and are easily corroded by water or HF. Batteries within the water content range of the positive and negative electrode plates of the present application have minimal damage to the silicon-based material, and the silicon-based material has a high theoretical capacity, resulting in excellent energy density and cycle performance.

[0105] It can be understood that silicon-based materials refer to materials containing silicon. As an example, silicon-based materials include but are not limited to elemental silicon, silicon oxide compounds, silicon-carbon composites, lithium-containing silicon-carbon materials, lithium-containing silicon oxide materials, magnesium-containing silicon-carbon materials and magnesium-containing silicon oxide materials, silicon-nitrogen composites and at least one of silicon alloys.

[0106] In some embodiments of the present application, the volume average particle size Dv50 of the silicon-based material is less than or equal to 6 μm. For example, the volume average particle size Dv50 of the silicon-based material can be 0.1 μm-5.9 μm, 0.5 μm-5.5 μm, 1 μm-5 μm, 1.5 μm-4.5 μm, 2 μm-4 μm, 2.5 μm-3.5 μm, etc. In other embodiments of the present application, the volume average particle size Dv50 of the silicon-based material is 3 μm-6 μm. Specifically, silicon-based materials are sensitive to water or HF generated by water due to the large number of hydroxyl groups on their surfaces, and are easily corroded by water or HF. The smaller the particle size of the silicon-based material, the more severe the corrosion. The present application controls the water content in the positive electrode and the negative electrode and controls the content of the first lithium salt in the electrolyte, which can inhibit the continuous increase of water in the electrolyte and reduce the corrosion of silicon-based materials by water. Therefore, small-particle silicon-based materials can be used in the battery system of the present application, and the volume average particle size Dv50 of the silicon-based material is controlled within the above range, which can shorten the diffusion path of lithium ions, reduce the impedance of the battery, increase the electrolyte infiltration area, and thus improve the low-temperature performance of the battery. It can also reduce the increase in the reaction area caused by the too low particle size of the silicon-based material, reduce the probability of side reactions, and improve the cycle life of the battery.

[0107] It is understood that the “volume average particle size Dv50 of the silicon-based material” is a well-known definition in the art and can be measured by methods well-known in the art. For example, it can be measured by the following method:

[0108] Referring to the standard GB / T 19077-2016, the volume average particle size Dv50 of the silicon-based material can be obtained by testing the silicon-based material using a laser particle size analyzer (such as Malvern Master Sizer 3000).

[0109] In some embodiments of the present application, based on the total mass of the negative electrode active material, the mass proportion of the silicon-based material is 1%-5%. For example, based on the total mass of the negative electrode active material, the mass proportion of the silicon-based material can be 1%-4.9%, 1.5%-4.5%, 2%-4%, 2.5%-3.5%, 2.5%-3%, etc. Specifically, the content of the silicon-based material is controlled within the above range. On the one hand, the silicon-based material has a high capacity and can reduce the coating thickness of the negative electrode active material layer on the negative electrode sheet under the condition of the same energy density, thereby effectively reducing the migration distance of lithium ions between the negative electrode active material layers, so that the efficiency of lithium ion transmission is high and the cycle life of the battery is improved. On the other hand, since the first lithium salt can absorb part of the water in the positive electrode sheet and the negative electrode sheet into the electrolyte, controlling the amount of silicon-based material added can reduce the increase in the probability of contact with water caused by excessive addition of silicon-based material, further reduce the damage of water to the silicon-based material, and improve the cycle life of the battery.

[0110] It is understood that “the mass proportion of the silicon-based material based on the total mass of the negative electrode active material” is a well-known definition in the art and can be measured by methods well-known in the art. For example, it can be measured by the following method:

[0111] The negative electrode was scraped and dissolved with nitric acid. Elemental analysis was performed using inductively coupled plasma optical emission spectrometry (ICP, Ametek, model: SPECTROARCOSICP-OES) according to standards YS / T1006.2-2014, GB / T23367.2-2009 or YS / T1028.5-2015 to determine the composition and content of silicon, thereby obtaining the mass percentage of the silicon-based material.

[0112] In some embodiments of the present application, the negative electrode active material further includes a second negative electrode active material, wherein the second negative electrode active material comprises at least one of artificial graphite, natural graphite, soft carbon, hard carbon, a silicon-based material, a tin-based material, or lithium titanate. As a result, the second negative electrode active material has high stability, further improving the cycle life of the battery.

[0113] In some embodiments, the tin-based material may be selected from at least one of elemental tin, tin oxide compounds, and tin alloys. However, the present application is not limited to these materials; other conventional materials that can be used as negative electrode active materials for batteries may also be used. These negative electrode active materials may be used singly or in combination of two or more.

[0114] In some embodiments of the present application, the volume average particle size Dv50 of the second negative electrode active material is 15 μm-20 μm. For example, the volume average particle size Dv50 of the second negative electrode active material can be 15 μm-19.9 μm, 15.5 μm-19.5 μm, 16 μm-18 μm, 16.5 μm-17.5 μm, etc. Thus, by combining the above-mentioned relatively large-particle-sized second negative electrode active material with a small-particle-sized silicon-based material, the dynamic performance of the battery can be improved, and the cycle life of the battery can be increased.

[0115] In some embodiments of the present application, the porosity of the negative electrode sheet is 15%-25%. For example, the porosity of the negative electrode sheet can be 15%-24%, 16%-23%, 17%-22%, 18%-21%, 19%-20%, etc. Specifically, controlling the porosity of the negative electrode sheet within the above range can, on the one hand, improve the dynamic performance of the battery and increase the cycle life. On the other hand, within the above porosity range of the negative electrode sheet, the negative electrode sheet is easy to dry to achieve a water content of 50ppm-200ppm, which can improve the cycle life of the battery.

[0116] It is understood that the “porosity of the negative electrode sheet” is a well-known definition in the art and can be measured by methods well-known in the art. For example, it can be measured by the following method:

[0117] The porosity of the negative electrode is determined by the gas displacement method. Specifically, refer to GB / T 24586-2009 and follow the steps below: Immerse the negative electrode in ethyl methyl carbonate (EMC) for cleaning. A true density analyzer (AccuPyc II 1340) is used to measure the porosity. The percentage of pore volume in the electrode to the total electrode volume is the electrode porosity, calculated as: Porosity = (V - V0) / V × 100%, where V0 is the true volume and V is the apparent volume.

[0118] In some embodiments of the present application, the electrolyte further comprises a second lithium salt, which comprises at least one of LiPF6, lithium difluorooxalatoborate (LiDFOB), lithium dioxalatoborate (LiBOB), or LiClO4. Specifically, a small amount of the second lithium salt can react with a trace amount of water entering the electrolyte (the first lithium salt absorbs a moderate amount of water from the positive and negative electrode plates into the electrolyte). The resulting substance can inhibit the decomposition of the first and second lithium salts in the electrolyte that do not participate in the reaction, thereby stabilizing the lithium salts and improving the battery's cycle performance. In addition, the second lithium salt that participates in the reaction can consume water that enters the electrolyte during the battery cycle, reducing the impact of excessive water on the battery cycle. Specifically, taking LiPF6 as an example, a small amount of LiPF6 can react with a trace amount of water to form LiPO2F2, which can inhibit the decomposition of LiPF6 that does not participate in the reaction, thereby stabilizing the LiPF6 that does not participate in the reaction in the electrolyte.

[0119] In some embodiments of the present application, the electrolyte further includes an additive, comprising at least one of LiPO2F2 or LiSO3F. Thus, the additive can further stabilize the electrolyte, reduce the probability of decomposition of the lithium salt (the first lithium salt and the second lithium salt, or the first lithium salt), and thus improve the cycle life of the battery. The additives LiPO2F2 or LiSO3F can be added proactively or generated from other substances.

[0120] In some embodiments of the present application, based on the total mass of the electrolyte, the mass proportion of the LiPO2F2 is 0.1%-0.5%. For example, based on the total mass of the electrolyte, the mass proportion of the LiPO2F2 can be 0.1%-0.49%, 0.1%-0.4%, 0.2%-0.3%, etc. Specifically, controlling the mass proportion of LiPO2F2 in the electrolyte within the above range can further stabilize the electrolyte, reduce the probability of decomposition of the lithium salt (the first lithium salt and / or the second lithium salt), and improve the cycle life of the battery.

[0121] In other embodiments of the present application, based on the total mass of the electrolyte, the mass proportion of the LiPO2F2 is less than or equal to 0.2%. The above content may be the content of LiPO2F2 in the battery electrolyte after formation. During the formation process, LiPO2F2 may participate in the formation of the SEI film or may be passively generated. By controlling the mass proportion of LiPO2F2 in the electrolyte of the battery after formation within the above range, the electrolyte can be further stabilized, the probability of decomposition of the lithium salt (the first lithium salt and the second lithium salt or the first lithium salt) can be reduced, and the cycle life of the battery can be improved.

[0122] It is understood that "the mass proportion of LiPO2F2 based on the total mass of the electrolyte" is a well-known definition in the art and can be measured by methods well-known in the art, for example, the following method can be used for measurement:

[0123] With reference to the standard JY / T020-1996 "General Rules for Ion Chromatography Analysis Methods", the mass proportion of LiPO2F2 in the electrolyte was determined by ion chromatography (model Thermo Nicolet IS10).

[0124] In some embodiments of the present application, the mass percentage of the LiSO3F is 0.1%-0.5% based on the total mass of the electrolyte. For example, the mass percentage of the LiSO3F can be 0.1%-0.49%, 0.1%-0.4%, 0.2%-0.3%, etc., based on the total mass of the electrolyte. Specifically, controlling the mass percentage of LiSO3F in the electrolyte within the above range can further stabilize the electrolyte, reduce the probability of decomposition of the lithium salt (the first lithium salt and / or the second lithium salt), and thus improve the cycle life of the battery.

[0125] In other embodiments of the present application, the mass percentage of the LiSO3F is less than or equal to 0.1% based on the total mass of the electrolyte. The above content may be the content of LiSO3F in the battery electrolyte after formation. During the formation process, LiSO3F may participate in the formation of the SEI film or may be passively generated. Controlling the mass percentage of LiSO3F in the battery electrolyte after formation within the above range can further stabilize the electrolyte, reduce the probability of decomposition of the lithium salt (the first lithium salt and the second lithium salt or the first lithium salt), and improve the cycle life of the battery.

[0126] It is understood that "the mass proportion of LiSO3F based on the total mass of the electrolyte" is a well-known definition in the art and can be measured by methods well-known in the art. For example, it can be measured by the following method:

[0127] With reference to the standard JY / T020-1996 "General Rules for Ion Chromatography Analysis Methods", the mass proportion of LiPO2F2 in the electrolyte was determined by ion chromatography (model Thermo Nicolet IS10).

[0128] 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 metal 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.

[0129] The positive electrode sheet includes a positive electrode current collector and a positive electrode active material layer disposed on at least one surface of the positive electrode current collector, wherein the positive electrode active material layer includes the positive electrode active material described in the present application.

[0130] 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.

[0131] In some embodiments, the positive electrode current collector may be a metal foil or a composite current collector. For example, aluminum foil may be used as the metal foil. The composite current collector may include a polymer material base and a metal layer formed on at least one surface of the polymer material base. The composite current collector may be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0132] In some embodiments of the present application, the positive electrode active material includes LiMn x Fe 1-x-y M y Composite material of PO4 and carbon.

[0133] In some embodiments of the present application, the positive electrode active material further includes 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)), or lithium nickel cobalt aluminum oxide (such as LiNi 0.8 Co 0.15 Al 0.05 O2) at least one.

[0134] The battery's charge and discharge processes involve the intercalation and deintercalation of lithium, leading to different molar Li contents at different discharge states. The molar Li contents listed in this application for the positive electrode active materials refer to the initial state of the material, i.e., the state before addition of the materials. When the positive electrode active materials are used in a battery system, the molar Li content will change after charge and discharge cycles.

[0135] In the list of positive electrode active materials in this application, the molar content of oxygen is only a theoretical value. Lattice oxygen release will cause the molar content of oxygen to change, and the actual molar content of oxygen will fluctuate.

[0136] 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, or a fluorine-containing acrylate resin.

[0137] 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, or carbon nanofibers.

[0138] 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, the binder and any other components, 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.

[0139] In some embodiments of the present application, the negative electrode plate includes a negative electrode current collector and a negative electrode active material layer provided on at least one side of the negative electrode current collector.

[0140] As an example, the negative electrode current collector has two surfaces facing each other in its thickness direction, and the negative electrode active material layer is provided on either or both of the two facing surfaces of the negative electrode current collector.

[0141] In some embodiments, 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 base layer and a metal layer formed on at least one surface of the polymer base material. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy, etc.) on a polymer base material (such as a base material of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0142] In some embodiments, the negative electrode active material layer may further include a binder. The binder may be selected from 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).

[0143] In some embodiments, the negative electrode active material layer may further include a conductive agent, which may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0144] In some embodiments, the negative electrode active material layer may further optionally include other additives, such as a thickener (eg, sodium carboxymethyl cellulose (CMC-Na)).

[0145] In some embodiments, 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 current collector, and after drying, cold pressing and other processes, the negative electrode sheet can be obtained.

[0146] In some embodiments of the present application, the electrolyte includes an electrolyte salt, a solvent, and an additive.

[0147] In some embodiments of the present application, the electrolyte salt, i.e., the lithium salt mentioned above, may further include at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium hexafluoroarsenate, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorobis(oxalatophosphate), or lithium tetrafluorooxalatophosphate.

[0148] In some embodiments, the solvent can be selected from at least one of ethylene carbonate, propylene carbonate, ethyl methyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methylpropyl carbonate, ethylpropyl 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, methyl ethyl sulfone and diethyl sulfone.

[0149] In some embodiments of the present application, the electrolyte further includes additives. For example, the additives may include negative electrode film-forming additives, positive electrode film-forming additives, and additives capable of improving certain battery properties, such as additives that improve battery overcharge performance, and additives that improve battery high or low temperature performance.

[0150] 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.

[0151] In some embodiments of the present application, the material of the separator may include at least one of glass fiber, non-woven fabric, polyethylene, polypropylene, or polyvinylidene fluoride. The separator may be a single-layer film or a multi-layer composite film, without particular limitation. When the separator is a multi-layer composite film, the materials of each layer may be the same or different, without particular limitation.

[0152] The battery of the present application includes a battery cell form, a battery module form and a battery pack form. The battery cell, battery module and battery pack of the present application are described below with reference to the accompanying drawings as appropriate.

[0153] In some embodiments of the present application, the positive electrode sheet, the negative electrode sheet, and the separator can be made into an electrode assembly through a winding process or a lamination process.

[0154] In some embodiments of the present application, the battery cell may include an outer packaging, which may be used to encapsulate the electrode assembly and the electrolyte.

[0155] In some embodiments of the present application, the outer packaging of the battery cell may be a hard shell, such as a hard plastic shell, an aluminum shell, or a steel shell. The outer packaging of the secondary battery may also be a soft shell, such as a pouch-type soft shell. The soft shell may be made of plastic, such as polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0156] The present application has no particular limitation on the shape of the battery cell, which may be cylindrical, square, or any other shape. For example, FIG1 shows a battery cell 1 having a square structure as an example.

[0157] In some embodiments of the present application, referring to Figure 2, the outer packaging may include a shell 11 and a cover plate 13. The shell 11 may include a bottom plate and side plates connected to the bottom plate, and the bottom plate and the side plates enclose a receiving cavity. The shell 11 has an opening connected to the receiving cavity, and the cover plate 13 can be covered on the opening to close the receiving cavity. The positive electrode sheet, the negative electrode sheet and the isolation membrane can form an electrode assembly 12 through a winding process or a lamination process. The electrode assembly 12 is encapsulated in the receiving cavity. The electrolyte is infiltrated in the electrode assembly 12. The number of electrode assemblies 12 contained in the battery cell 1 can be one or more, and those skilled in the art can select according to specific actual needs.

[0158] The second aspect of the present application provides a method for preparing the battery described in the first aspect, comprising:

[0159] S100, assembling the positive electrode sheet and the negative electrode sheet into a bare cell, injecting electrolyte to obtain a battery;

[0160] Wherein, based on the total mass of the positive electrode plate, the mass proportion of water is 50ppm-300ppm, based on the total mass of the negative electrode plate, the mass proportion of water is 30ppm-200ppm; the electrolyte includes a first lithium salt, and the first lithium salt includes: LiN(SO2R)2,

[0161] Wherein, R includes at least one of F or a hydrocarbon group of 1 to 3 carbon atoms substituted by F, and based on the total mass of the electrolyte, the mass proportion of the first lithium salt is 3% to 10%.

[0162] Therefore, the battery prepared in the present application controls the mass proportion of water in the positive electrode plate, adds a first lithium salt to the electrolyte and controls its content. The first lithium salt can absorb the above-mentioned part of the water in the positive electrode plate into the electrolyte in an appropriate amount. This part of water is helpful for the formation of the battery SEI film and the improvement of the battery cycle performance; and it prevents too much water from entering the electrolyte from the positive electrode plate, which can improve the stability of the electrolyte and increase the cycle life of the battery.

[0163] In some embodiments of the present application, before injecting the electrolyte, the process further includes drying the bare cell. Thus, by controlling the water content in the positive electrode sheet and / or the negative electrode sheet through drying, the cycle life of the battery can be increased.

[0164] In some embodiments of the present application, the water content in the positive electrode and / or negative electrode of the battery can be controlled by drying conditions such as drying method, drying temperature, drying time, etc. Drying can be performed at normal pressure, reduced pressure, microwave, infrared, etc. In other embodiments of the present application, drying is performed at normal pressure.

[0165] In some embodiments of the present application, the drying temperature is 100°C-120°C. For example, the drying temperature may be 100°C-119°C, 105°C-115°C, 110°C-115°C, etc. Thus, within the above drying temperature range, it is beneficial to control the water content in the positive electrode sheet and the negative electrode sheet within a limited range. As a result, the first lithium salt can appropriately absorb a portion of the water in the positive electrode sheet and the negative electrode sheet into the electrolyte. This water contributes to the formation of the battery SEI film and the improvement of the battery cycle performance. In addition, the amount of water entering the electrolyte from the negative electrode sheet is reduced, thereby improving the stability of the electrolyte and further increasing the cycle life of the battery.

[0166] In some embodiments of the present application, the drying time is 10 hours to 20 hours. For example, the drying time may be 10 hours to 19 hours, 11 hours to 18 hours, 12 hours to 17 hours, 13 hours to 16 hours, 14 hours to 15 hours, etc. Thus, within the above drying time range, it is beneficial to control the water content in the positive electrode sheet and the negative electrode sheet within a limited range, and then the first lithium salt can appropriately absorb a portion of the water in the positive electrode sheet and the negative electrode sheet into the electrolyte. This water helps to form the SEI film of the battery and improve the battery cycle performance; and it also prevents excessive water from entering the electrolyte from the negative electrode sheet. Moreover, due to the stability of the first lithium salt itself, the stability of the electrolyte can be improved, which can further improve the cycle life of the battery.

[0167] When the positive electrode active material is a lithium iron phosphate material, it is difficult to dry after being prepared into a positive electrode plate. Controlling the drying temperature and time within the above range is more conducive to controlling the water content in the positive electrode plate within a limited range, which can improve the stability of the electrolyte and further improve the cycle life of the battery.

[0168] Specifically, the positive electrode sheet, separator, and negative electrode sheet are stacked in order, with the separator placed between the positive electrode sheet and the negative electrode sheet to serve as an isolation, and then wound to obtain an electrode assembly; the electrode assembly is placed in an outer packaging shell, dried according to the above-mentioned drying conditions, and then injected with electrolyte, and after vacuum packaging, standing and other processes, a lithium-ion battery is obtained.

[0169] In some embodiments of the present application, after injecting the electrolyte, the method further includes: forming the battery.

[0170] In some embodiments of the present application, battery cells may be assembled into a battery module. The number of battery cells contained in a battery module may be one or more. The specific number may be selected by those skilled in the art according to the application and capacity of the battery module.

[0171] Figure 3 shows an example battery module 2. Referring to Figure 3 , within the battery module 2, multiple battery cells 1 may be arranged sequentially along the length of the battery module 2. Of course, they may also be arranged in any other manner. Furthermore, the multiple battery cells 1 may be secured together using fasteners.

[0172] In some embodiments of the present application, the battery module 2 may further include a housing having a receiving space, and the plurality of battery cells 1 may be received in the receiving space.

[0173] In some embodiments of the present application, the above-mentioned battery modules can also be assembled into a battery pack. The number of battery modules contained in the battery pack can be one or more. The specific number can be selected by those skilled in the art according to the application and capacity of the battery pack.

[0174] Figures 4 and 5 illustrate an example battery pack 3. Referring to Figures 4 and 5 , the battery pack 3 may include a battery box and multiple battery modules 2 disposed within the battery box. The battery box comprises an upper case 31 and a lower case 32. The upper case 31 can be positioned over the lower case 32 to form an enclosed space for accommodating the battery modules 2. The multiple battery modules 2 can be arranged in any manner within the battery box.

[0175] In addition, the present application also provides an electrical device, which includes at least one of the battery described in the first aspect of the present application, the battery prepared by the method described in the second aspect, the battery described in the third aspect, or the battery prepared by the method described in the fourth aspect. The battery cell, battery module, or battery pack can be used as a power source for the electrical device, and can also be used as an energy storage unit for the electrical device. The electrical device may include mobile devices (such as mobile phones, laptops, etc.), electric vehicles (such as pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc., but is not limited thereto.

[0176] As the electrical device, a battery cell, a battery module or a battery pack can be selected according to its usage requirements.

[0177] Figure 6 shows an example of an electric device. This device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. To meet the high power and high energy density requirements of the secondary battery, a battery pack or battery module can be used.

[0178] Another example device may be a mobile phone, a tablet computer, a notebook computer, etc. Such a device is usually required to be lightweight and thin, and may use a battery cell as a power source.

[0179] Below, the embodiment of the present application is described. The embodiment described below is exemplary and is only used to explain the present application, and is not to be construed as limiting the present application. Where specific techniques or conditions are not specified in the embodiments, the techniques or conditions described in the literature in this area or the product specifications are used. Reagents or instruments used that do not specify the manufacturer are conventional products that can be obtained commercially.

[0180] Example 1

[0181] 1. Preparation of positive electrode sheet

[0182] The positive electrode active material LiFePO4 (BET specific surface area 12m 2 / g, based on the total mass of the positive electrode active material, the mass proportion of the carbon coating material is 1.2%, and the thickness of the carbon coating material is 2μm), the binder polyvinylidene fluoride, and the conductive agent acetylene black are mixed in a weight ratio of 98:1:1 and dissolved in a solvent N-methylpyrrolidone (NMP) to form a positive electrode slurry, and then the slurry is coated on the current collector aluminum foil. After drying, it is cold pressed, trimmed, cut into pieces, and striped to make the positive electrode sheet of the lithium-ion battery.

[0183] 2. Preparation of negative electrode sheet

[0184] The negative electrode active material (silicon-containing material SiO2 (volume average particle size Dv50, 6 μm): graphite (volume average particle size Dv50, 17.5 μm) = 5:95), conductive agent carbon black, thickener CMC, binder styrene-butadiene rubber (SBR), and ceramic material are mixed in a weight ratio of 95:2:1:1:1 and dissolved in deionized water to form a negative electrode slurry. The slurry is then applied to a current collector copper foil, dried, and cold-pressed, trimmed, cut, and slit to form the negative electrode sheet for the lithium-ion battery. The porosity of the negative electrode sheet is 20%.

[0185] 3. Preparation of electrolyte

[0186] The reaction was carried out in an argon atmosphere glove box with a water content of <10ppm. First, the non-aqueous solvent EC (ethylene carbonate): DMC (dimethyl carbonate): EMC (ethyl methyl carbonate) was mixed in a mass ratio of 30:50:20, and then lithium salts (LiFSI and LiPF6) were added. Finally, 2% of the additive VC (vinylene carbonate) of the total mass of the electrolyte, 0.1% of the total mass of the electrolyte LiPO2F2 and 0.1% of the total mass of the electrolyte LiSO3F were added to complete the preparation of the electrolyte. Based on the total mass of the electrolyte, the mass proportion of LiFSI was 7%, and the mass proportion of LiPF6 was 12.5%.

[0187] 4. Isolation film

[0188] A polyethylene (PE) film with a thickness of 10 μm was used as the separator.

[0189] 5. Preparation of secondary batteries

[0190] Prepare the above-mentioned positive electrode sheet, separator, and negative electrode sheet in order, so that the separator is placed between the positive electrode sheet and the negative electrode sheet to play an isolating role, then wind to obtain a bare battery cell, and weld the tabs; place the bare battery cell in an outer packaging shell, dry it at 110°C for 13 hours, and then inject the electrolyte. After vacuum packaging, standing, forming, shaping and other processes, a lithium-ion battery is obtained.

[0191] The preparation methods of the lithium-ion batteries of Examples 2-15 and Comparative Examples 1-4 are the same as those of Example 1, except that the process of preparing the positive electrode sheet is different. As shown in Table 1, in the electrolyte of Example 15, the mass ratio of LiBOB and LiPF6 in the second lithium salt is 1:1.

[0192] Table 1

[0193] The batteries of Examples 1-15 and Comparative Examples 1-4 were subjected to a capacity retention test after 1.2C cycles. The test results are shown in Table 2.

[0194] At 25°C, charge the battery to 3.65V at 0.33C, then discharge it to 2.0V at 0.33C. Record the discharge capacity at this time as U0. Then, charge the battery to 3.65V at 1.2C, then discharge it to 2.0V at 0.33C. Repeat this for 800 cycles and measure the discharge capacity at this time as U1.

[0195] Then the battery capacity retention rate E = (U0-U1) / U0×100%.

[0196] Table 2

[0197] Conclusion: Comparing Examples 1-15 and Comparative Example 1-4, in Example 1-15, controlling the mass ratio of water in the positive and negative electrode sheets, and adding a first lithium salt to the electrolyte and controlling its content can improve the cycle performance of the battery. Comparative Example 1-4 does not simultaneously control the electrode sheet water content and the first lithium salt content, and the battery cycle performance is significantly reduced. It can be seen that the present application simultaneously controls the electrode sheet water content and the first lithium salt content, which can significantly reduce the continuous increase in the water content in the electrolyte, thereby reducing the damage caused by the generation of HF in the electrolyte to the positive and negative electrodes of the battery, and improving the cycle life of the battery.

[0198] It should be noted that the present application is not limited to the above-mentioned embodiments. The above-mentioned embodiments are merely examples, and any embodiments having substantially the same structure and effect as the technical concept within the scope of the present application are all included in the technical scope of the present application. In addition, without departing from the scope of the present application, any other embodiments that can be conceived by those skilled in the art and that combine some of the constituent elements in the embodiments are also included in the scope of the present application.

Claims

1. A battery, wherein: The invention comprises a positive electrode sheet, a negative electrode sheet and an electrolyte, wherein the mass proportion of water is 50ppm-300ppm based on the total mass of the positive electrode sheet, and the mass proportion of water is 30ppm-200ppm based on the total mass of the negative electrode sheet; the electrolyte comprises a first lithium salt, and the first lithium salt comprises: LiN(SO2R)2, Wherein, R includes at least one of F or a hydrocarbon group of 1 to 3 carbon atoms substituted by F, and based on the total mass of the electrolyte, the mass proportion of the first lithium salt is 3% to 10%.

2. The battery according to claim 1, wherein Based on the total mass of the positive electrode sheet, the mass proportion of water is 100ppm-300ppm.

3. The battery according to claim 1 or 2, wherein Based on the total mass of the positive electrode plate, the mass proportion of water is 100ppm-250ppm.

4. The battery according to any one of claims 1 to 3, wherein Based on the total mass of the negative electrode plate, the mass proportion of water is 50ppm-200ppm.

5. The battery according to any one of claims 1 to 4, wherein Based on the total mass of the negative electrode plate, the mass proportion of water is 50ppm-150ppm.

6. The battery according to claim 1, wherein Based on the total mass of the positive electrode sheet, the mass proportion of water is 50ppm-250ppm.

7. The battery according to claim 1 or 6, wherein Based on the total mass of the positive electrode sheet, the mass proportion of water is 50ppm-220ppm.

8. The battery according to any one of claims 1, 6 and 7, wherein Based on the total mass of the negative electrode plate, the mass proportion of water is 30ppm-150ppm.

9. The battery according to any one of claims 1, 6, 7, and 8, wherein Based on the total mass of the negative electrode plate, the mass proportion of water is 30ppm-110ppm.

10. The battery according to any one of claims 1 to 9, wherein The first lithium salt includes at least one of lithium bis(fluorosulfonyl)imide and lithium bis(trifluoromethanesulfonyl)imide.

11. The battery according to any one of claims 1 to 10, wherein The positive electrode sheet includes a positive electrode active material, and the positive electrode active material includes LiMn x Fe 1-x-y M y PO4, wherein 0≤x≤1, 0≤y≤0.04, and M includes at least one of Ti, Mg, Ta, Sc, Cr, Y, Zr, Nb, Mo, La, Ta, W, Hf, V, Ni, Rh, or Os.

12. The battery according to claim 11, wherein The BET specific surface area of ​​the positive electrode active material is 10 m 2 / g-15m 2 / g.

13. The battery according to claim 11 or 12, wherein The positive electrode active material also includes a LiMn x Fe 1-x-y M y A coating material covering at least a portion of the surface of PO 4 , wherein the coating material comprises carbon.

14. The battery according to claim 13, wherein Based on the total mass of the positive electrode active material, the mass proportion of the coating material is 0.8%-3.5%.

15. The battery according to claim 13 or 14, wherein Based on the total mass of the positive electrode active material, the mass proportion of the coating material is 1.3%-2.5%.

16. The battery according to any one of claims 1 to 15, wherein The negative electrode plate includes a negative electrode active material, and the negative electrode active material includes a silicon-based material.

17. The battery according to claim 16, wherein The volume average particle size Dv50 of the silicon-based material is less than or equal to 6 μm.

18. The battery according to claim 16 or 17, wherein The volume average particle size Dv50 of the silicon-based material is 3 μm-6 μm.

19. The battery according to any one of claims 16 to 18, wherein Based on the total mass of the negative electrode active material, the mass proportion of the silicon-based material is 1%-5%.

20. The battery according to any one of claims 16 to 19, wherein The negative electrode active material further includes a second negative electrode active material, and the second negative electrode active material includes at least one of artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based material, tin-based material or lithium titanate.

21. The battery according to claim 20, wherein The volume average particle size Dv50 of the second negative electrode active material is 15 μm-20 μm.

22. The battery according to any one of claims 1 to 21, wherein The porosity of the negative electrode plate is 15%-25%.

23. The battery according to any one of claims 1 to 22, wherein The electrolyte further includes a second lithium salt, wherein the second lithium salt includes at least one of LiPF6, lithium difluorooxalatoborate, lithium dioxalatoborate or LiClO4.

24. The battery according to any one of claims 1 to 23, wherein The electrolyte further includes an additive, wherein the additive includes at least one of LiPO2F2 or LiSO3F.

25. The battery according to claim 24, wherein One or more of the following conditions are met: Based on the total mass of the electrolyte, the mass proportion of the LiPO2F2 is 0.1%-0.5%; Based on the total mass of the electrolyte, the mass proportion of the LiSO 3 F is 0.1%-0.5%.

26. The battery according to claim 24, wherein One or more of the following conditions are met: Based on the total mass of the electrolyte, the mass proportion of the LiPO2F2 is less than or equal to 0.2%; Based on the total mass of the electrolyte, the mass proportion of the LiSO 3 F is less than or equal to 0.1%.

27. The battery according to any one of claims 1 to 26, wherein Based on the total mass of the electrolyte, the mass proportion of the first lithium salt is 5%-10%.

28. A method for preparing a battery, wherein: include: Assembling the positive electrode sheet and the negative electrode sheet into a bare cell, injecting electrolyte to obtain a battery; Wherein, based on the total mass of the positive electrode sheet, the mass proportion of water is 50ppm-300ppm, and based on the total mass of the negative electrode sheet, the mass proportion of water is 30ppm-200ppm; the electrolyte includes a first lithium salt, and the first lithium salt includes: LiN(SO2R)2, Wherein, R includes at least one of F or a hydrocarbon group of 1 to 3 carbon atoms substituted by F, and based on the total mass of the electrolyte, the mass proportion of the first lithium salt is 3% to 10%.

29. The method according to claim 28, wherein Before injecting the electrolyte, it also includes: The bare battery cell is dried.

30. The method according to claim 29, wherein One or more of the following conditions are met: The drying temperature is 100°C-120°C; The drying time is 10h-20h.

31. The method according to any one of claims 28 to 30, wherein After injecting the electrolyte, it also includes: The battery is obtained.

32. An electrical device, wherein: A battery comprising the battery according to any one of claims 1 to 27 or a battery made by the method according to any one of claims 28 to 31.

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