Secondary battery and electric device

Abstract

Provided are a secondary battery and an electric device. The secondary battery comprises a positive electrode sheet, a negative electrode sheet and an electrolyte, wherein the positive electrode sheet comprises a positive-electrode current collector and a positive-electrode active material layer, and the negative electrode sheet comprises a negative-electrode current collector and a negative-electrode active material layer; the coating weight of the positive-electrode active material layer is Wz, the coating weight of the negative-electrode active material layer is Wf, and Wz and Wf satisfy: 1.6Wf≤Wz≤2.2Wf, and 3.25 mg / cm2≤Wf≤5.84 mg / cm2; the positive-electrode current collector integrally extends to form a plurality of positive electrode tabs, and the negative-electrode current collector integrally extends to form a plurality of negative electrode tabs; and the electrolyte comprises an organic solvent, a lithium salt and an additive, the organic solvent comprises a chain carboxylic ester compound, and based on the mass of the electrolyte, the mass percentage content of the chain carboxylic ester compound is 6% to 56%. By means of the arrangement, the secondary battery has a low temperature rise during charging on the basis of improving the charging speed of the secondary battery, thereby improving the dynamic performance of the secondary battery.

Description

Secondary battery and power-consuming device Technical Field

[0001] The present application relates to the field of electrochemical technology, and in particular to a secondary battery and an electrical device. Background Art

[0002] Lithium-ion batteries have the characteristics of high specific energy, high operating voltage, low self-discharge rate, small size and light weight. They are widely used in various fields such as energy storage, portable electronic devices and electric vehicles.

[0003] With the continuous iterative development of consumer lithium-ion batteries in recent years, the market has increasingly higher requirements for their charging speed and charging rate. Therefore, how to reduce the impedance of various components of lithium-ion batteries and increase the charging speed of lithium-ion batteries to meet the requirements of super-fast charging while maintaining a low temperature rise has become a technical problem that technicians in this field urgently need to solve.

[0004] Summary of the Invention

[0005] The purpose of this application is to provide a secondary battery that improves the charging speed of the secondary battery while taking into account the low charging temperature rise of the secondary battery, thereby improving the dynamic performance and cycle performance of the secondary battery, and at the same time provides an electrical device using the secondary battery.

[0006] It should be noted that in the invention content of this application, lithium-ion batteries are used as an example of secondary batteries to explain this application. However, the secondary batteries of this application are not limited to lithium-ion batteries, but can also be applied to secondary batteries such as sodium-ion batteries. The specific technical solutions are as follows:

[0007] The first aspect of the present application provides a secondary battery, which includes a positive electrode sheet, a negative electrode sheet and an electrolyte, wherein the positive electrode sheet includes a positive electrode current collector and a positive electrode active material layer, and the negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer; the coating weight of the positive electrode active material layer is W z The coating weight of the negative electrode active material layer is W f , W z and W f Between: 1.6W f ≤W z ≤2.2W f 、3.25mg / cm 2 ≤W f ≤5.84mg / cm 2. The positive electrode current collector extends integrally to form a plurality of positive electrode tabs, and the negative electrode current collector extends integrally to form a plurality of negative electrode tabs. The electrolyte includes an organic solvent, a lithium salt and an additive, and the organic solvent includes a chain carboxylic acid ester compound. Based on the mass of the electrolyte, the mass percentage of the chain carboxylic acid ester compound is 6% to 56%. With the above-mentioned structural design of the positive electrode tabs and the negative electrode tabs, multiple current channels can be generated on the positive electrode sheet and the negative electrode sheet during the secondary battery cycle, thereby reducing the internal resistance of the secondary battery, making the voltage polarization of the secondary battery small under fast charging conditions, reducing the charging temperature rise of the secondary battery, and shortening the charging time of the secondary battery.

[0008] By regulating the coating weight of the positive electrode active material layer and the negative electrode active material layer within the above range, the thickness of the positive electrode active material layer and the negative electrode active material layer can be reduced, and while taking into account the processing performance and energy density of the secondary battery, the transmission distance of lithium ions inside the positive electrode sheet and the negative electrode sheet can be reduced, thereby reducing the ohmic polarization and concentration polarization of the secondary battery, improving the fast charging performance, and making the secondary battery have higher dynamic performance. In order to adapt to the high dynamic performance of the secondary battery, higher requirements are placed on the electrolyte in the secondary battery. The lithium ion transmission speed in conventional electrolytes is slow under the high dynamic system of the secondary battery, resulting in a slow charging speed of the secondary battery, and easy lithium precipitation during the cycle, resulting in reduced cycle performance of the secondary battery. By regulating the composition and content in the electrolyte, the electrolyte has high conductivity and low viscosity, which can accelerate the transmission speed of lithium ions and further reduce the electrochemical polarization and concentration polarization of the secondary battery. This application optimizes the electrochemical system by combining the structural design of the positive electrode tab and the negative electrode tab, the coating weight of the positive electrode active material layer and the negative electrode active material layer, and the composition and content of the electrolyte. It can improve the charging speed of the secondary battery while taking into account the low charging temperature rise of the secondary battery, thereby improving the kinetic performance and cycle performance of the secondary battery.

[0009] In some embodiments of the present application, 6.49 mg / cm 2 ≤W z ≤11.69 mg / cm 2 The present application adjusts the coating weight of the positive electrode active material layer within the scope of the present application, while taking into account the processing performance and energy density of the secondary battery, shortens the transmission distance of lithium ions and electrons on the positive electrode sheet, reduces the impedance of the secondary battery, and enables the secondary battery to have good cycle performance.

[0010] In some embodiments of the present application, an N1 layer of positive electrode sheet is provided between two adjacent positive electrode tabs, and an N2 layer of negative electrode sheet is provided between two adjacent negative electrode tabs, and N1 and N2 are each independently selected from 0, 1, 2 or 3. Through the above-mentioned arrangement, the present application has multiple current channels on the positive electrode sheet and the negative electrode sheet, so that the impedance of the secondary battery is reduced, the voltage polarization of the secondary battery during fast charging is small, the charging temperature rise is reduced, and the charging time is shortened, so that the secondary battery has good dynamic performance and cycle performance. It can be understood that by adjusting N1 and N2 to 0, more current channels can be provided on the positive electrode sheet and the negative electrode sheet, which can further reduce the internal resistance of the secondary battery, further reduce the charging temperature rise of the fast-charging secondary battery, and further shorten the charging time, thereby further improving the dynamic performance of the fast-charging secondary battery while taking into account the cycle performance and mechanical reliability. However, this will reduce the energy density of the battery to a certain extent; adjusting N1 and N2 to 1 or 2 or 3 will reduce the number of tabs and increase the internal resistance to a certain extent, but can improve the energy density of the battery.

[0011] In some embodiments of the present application, the chain carboxylate compound includes at least one of methyl formate, methyl acetate, ethyl formate, ethyl acetate, propyl acetate, ethyl propionate, methyl propionate, n-propyl propionate, isopropyl propionate, n-butyl propionate, isobutyl propionate, n-pentyl propionate, isopentyl propionate, ethyl butyrate, n-propyl butyrate, propyl isobutyrate, n-pentyl butyrate, n-pentyl isobutyrate, n-butyl butyrate, isobutyl isobutyrate, and n-pentyl valerate. Preferably, the chain carboxylate compound includes at least one of methyl formate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, or ethyl butyrate. By selecting the above-mentioned chain carboxylate compounds, the obtained electrolyte has high conductivity and low viscosity, which is conducive to the rapid transmission of lithium ions, thereby reducing the impedance of the secondary battery, reducing the charging temperature rise during fast charging of the secondary battery, shortening the charging time, and having good dynamic performance and cycle performance.

[0012] In some embodiments of the present application, the organic solvent further comprises at least one of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, γ-butyrolactone, or tetrahydrofuran, and the weight percentage of the organic solvent is 60% to 80% based on the weight of the electrolyte. By regulating the type and weight percentage of the organic solvent within the scope of the present application, the stability of the electrolyte is improved, thereby improving the kinetic performance and cycle performance of the secondary battery.

[0013] In some embodiments of the present application, the mass percentage of the lithium salt is 10% to 20% based on the mass of the electrolyte. By regulating the mass percentage of the lithium salt within the above range, the lithium salt has a higher solubility in the electrolyte, resulting in a higher conductivity of the electrolyte, thereby improving the kinetic performance and cycle performance of the secondary battery.

[0014] In some embodiments of the present application, the lithium salt includes at least one of lithium hexafluorophosphate, lithium difluorophosphate, lithium tetrafluoroborate, lithium hexafluoroarsenate, lithium perchlorate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium bis(oxalatoborate), or lithium difluorooxalatoborate. The use of the above-mentioned lithium salts can provide an electrolyte with higher conductivity, thereby improving the kinetic and cycling performance of the secondary battery.

[0015] In some embodiments of the present application, the additive includes at least one of succinonitrile, glutaronitrile, pimelonitrile, 1,2-bis(2-cyanoethoxy)ethane, 1,2-bis(2-cyanoethoxy)propane, or 1,2,3-tris(2-cyanoethoxy)propane, and the weight percentage of the additive is 2% to 10% based on the weight of the electrolyte. By regulating the type and weight percentage of the additive within the scope of this application, it is beneficial to form a protective electrolyte film (CEI) on the surface of the positive electrode, thereby improving the structural stability of the positive electrode, reducing the occurrence of side reactions in the electrolyte, and thus improving the high-temperature safety performance of the secondary battery.

[0016] The second aspect of the present application provides an electric device, which includes the secondary battery according to any one of the aforementioned embodiments. Therefore, the electric device has good performance.

[0017] Beneficial effects of this application:

[0018] The present application provides a secondary battery and an electrical device, wherein the electrochemical system is optimized by combining the structural design of the positive and negative electrode tabs, the coating weights of the positive and negative electrode active material layers, and the composition and content of the electrolyte. This allows for good synergy between the structural design of the positive and negative electrode tabs, the coating weights of the positive and negative electrode active material layers, and the electrolyte. This improves the charging speed of the secondary battery while also allowing for a low charging temperature rise, thereby improving the kinetic performance and cycle performance of the secondary battery. The electrical device of the present application has good performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] The drawings described herein are used to provide further understanding of the present application and constitute a part of the present application. The illustrative embodiments of the present application and their descriptions are used to explain the present application and do not constitute improper limitations on the present application.

[0020] FIG1 is a schematic structural diagram of an electrode assembly according to an embodiment of the present application;

[0021] FIG2 is a schematic structural diagram of an electrode assembly according to another embodiment of the present application;

[0022] FIG3 is a schematic diagram showing the positional relationship between the positive electrode sheet and the negative electrode sheet along the thickness direction of the positive electrode sheet according to an embodiment of the present application;

[0023] FIG4 is a schematic structural diagram of a positive electrode sheet according to an embodiment of the present application;

[0024] FIG5 is a schematic structural diagram of a negative electrode sheet according to an embodiment of the present application.

[0025] Figure numerals: electrode assembly 001; positive electrode sheet 10; positive electrode current collector 11; positive electrode active material layer 12; positive electrode tab 13; negative electrode sheet 20; negative electrode current collector 21; negative electrode active material layer 22; negative electrode tab 23; separator 30; positive electrode tab region 111; positive electrode main body region 112; negative electrode tab region 211; negative electrode main body region 212. DETAILED DESCRIPTION

[0026] To make the objectives, technical solutions, and advantages of this application more clearly understood, the present application is further described in detail below with reference to the accompanying drawings and examples. It is apparent that the described examples are only a portion of the embodiments of this application, rather than all of them. All other embodiments obtained by those skilled in the art based on this application are within the scope of protection of this application.

[0027] It should be noted that in the invention content of this application, lithium-ion batteries are used as an example of secondary batteries to explain this application, but the secondary batteries of this application are not limited to lithium-ion batteries, and can also be applied to secondary batteries such as sodium-ion batteries.

[0028] The first aspect of the present application provides a secondary battery, comprising a positive electrode sheet, a negative electrode sheet and an electrolyte, wherein the positive electrode sheet comprises a positive electrode current collector and a positive electrode active material layer, and the negative electrode sheet comprises a negative electrode current collector and a negative electrode active material layer. The coating weight of the positive electrode active material layer is W z The coating weight of the negative electrode active material layer is W f , W z and W f Between: 1.6W f ≤W z ≤2.2W f 、3.25mg / cm 2 ≤W f ≤5.84mg / cm 2 For example, W f 3.25 mg / cm 2, 3.5mg / cm 2 、3.75mg / cm 2 , 4mg / cm 2 , 4.25mg / cm 2 , 4.5mg / cm 2 , 4.75mg / cm 2 , 5mg / cm 2 , 5.25mg / cm 2 , 5.5mg / cm 2 , 5.84mg / cm 2 Or a range consisting of any two of the values. The positive electrode current collector extends integrally to form a plurality of positive electrode tabs, and the negative electrode current collector extends integrally to form a plurality of negative electrode tabs. The electrolyte comprises an organic solvent, a lithium salt, and an additive, the organic solvent comprises a chain carboxylate compound, and the mass percentage of the chain carboxylate compound is 6% to 56% based on the mass of the electrolyte, for example, the mass percentage of the chain carboxylate compound is 6%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 56%, or a range consisting of any two of the values.

[0029] In this application, for ease of understanding, the length direction of the positive electrode sheet in the unfolded state is defined as X, the width direction as Y, and the thickness direction as Z. It can be understood that the length direction, width direction, and thickness direction of the negative electrode sheet and the separator are the same as those of the positive electrode sheet in the unfolded state. After the positive electrode sheet, the separator, and the negative electrode sheet are wound to form an electrode assembly with a wound structure, the winding direction of the electrode assembly is W. As shown in Figures 1 to 5, along the winding direction W of the electrode assembly 001, the electrode assembly 001 includes a positive electrode sheet 10, a negative electrode sheet 20, and a separator 30. Along the thickness direction Z of the positive electrode sheet, the positive electrode sheet 10 includes a positive electrode collector 11 and a positive electrode active material layer 12 located on both surfaces of the positive electrode collector. The negative electrode sheet 20 includes a negative electrode collector 21 and a negative electrode active material layer 22 located on both surfaces of the negative electrode collector. The separator 30 is located between the positive electrode sheet 10 and the negative electrode sheet 20. As shown in FIG4 , the positive electrode sheet 10 includes a positive electrode current collector 11, which extends integrally to form a plurality of positive electrode tabs 12. The positive electrode current collector 11 includes a positive electrode tab region 111 and a positive electrode main body region 112. It is understood that the positive electrode tab region 111 is the region where the positive electrode tabs 12 are provided, and the positive electrode main body region 112 refers to the region of the positive electrode current collector 11 excluding the positive electrode tab region 111. As shown in FIG5 , the negative electrode sheet 20 includes a negative electrode current collector 21, which extends integrally to form a plurality of negative electrode tabs 22. The negative electrode current collector 21 includes a negative electrode tab region 211 and a negative electrode main body region 212. It is understood that the negative electrode tab region 211 refers to the region where the negative electrode tabs 22 are provided, and the negative electrode main body region 212 refers to the region of the negative electrode current collector 21 excluding the negative electrode tab region 211. In the present application, the above-mentioned "integrated extension" refers to the integral molding of the current collector and the tabs. For example, multiple tabs can be cut out on the current collector by die-cutting or laser, rather than connecting the tabs to the current collector by welding or other means. It should be noted that the number, shape and size of the positive and negative tabs in Figures 1, 2, 4 and 5 are only for illustrative purposes, and this application is not limited to this. In the present application, the above-mentioned "multiple" refers to two or more. In one embodiment of the present application, multiple refers to 2 to the same number as the number of electrode layers. For example, multiple can be 2, 3, 4, 5, 6, 7, 10, 15, 20, 25, 30.

[0030] At present, the market mostly adopts the embedded single-pole ear design, that is, there is only one positive electrode ear and one negative electrode ear in the secondary battery, and the positive electrode ear is welded to the positive electrode sheet, and the negative electrode ear is welded to the negative electrode sheet, which leads to crowding of the current channel in the positive electrode sheet or the negative electrode sheet, which is not conducive to the conduction of current, resulting in excessive internal resistance of the lithium-ion battery, temperature rise during fast charging of the lithium-ion battery, and poor dynamic performance. Compared with the conventional single-pole ear structure, the present application integrally forms a plurality of positive electrode current collector positions in the empty foil area of ​​the positive electrode sheet, and integrally forms a plurality of negative electrode current collector positions in the empty foil area of ​​the negative electrode sheet. Through the above-mentioned arrangement, multiple current channels are generated on the positive electrode sheet and the negative electrode sheet, so that the impedance of the secondary battery is reduced, the voltage polarization during fast charging of the secondary battery is smaller, the charging temperature rise of the secondary battery is reduced, the charging time of the secondary battery is shortened, and the requirements of fast charging are met. The coating weight of the positive active material layer is less than 1.6W f The coating weight of the negative electrode active material layer is too large relative to the coating weight of the positive electrode active material layer. When the potential of the secondary battery is reached, the lithium removal rate of the positive electrode increases significantly, resulting in a very high actual potential of the positive electrode and easy destruction of the structure. The positive electrode decays rapidly, resulting in the secondary battery being unable to cycle normally. The coating weight of the positive electrode active material layer is greater than 2.2W f If the coating weight of the positive electrode active material layer is too large relative to the coating weight of the negative electrode active material layer, the released lithium ions will be excessive, and the negative electrode will not be able to fully accept the released lithium ions from the positive electrode. The lithium ions cannot be properly embedded in the negative electrode sheet, which will lead to lithium deposition on the negative electrode sheet and affect the cycle dynamics performance of the secondary battery. The coating weight of the negative electrode active material layer is less than 3.25 mg / cm 2 , the energy density of the secondary battery is reduced, the service life is shortened, and it is difficult to meet the process requirements of the secondary battery; the coating weight of the negative electrode active material layer is greater than 5.84 mg / cm 2, the transmission distance of lithium ions inside the positive electrode sheet and / or the negative electrode sheet increases, and the impedance of the secondary battery increases. By regulating the coating weight of the positive electrode active material layer and the negative electrode active material layer within the above range, the thickness of the positive electrode active material layer and the negative electrode active material layer can be reduced, the porosity of the positive electrode active material layer and the negative electrode active material layer can be increased, and the transmission distance of lithium ions and electrons inside the positive electrode sheet and the negative electrode sheet can be shortened, thereby reducing the ohmic polarization and concentration polarization of the secondary battery, improving the fast charging performance, and making the secondary battery have higher kinetic performance. In order to adapt to the high kinetic performance of the secondary battery, higher requirements are placed on the electrolyte in the secondary battery. The lithium ion transmission speed in conventional electrolytes is slow under the high kinetic system of the secondary battery, resulting in a slow charging speed of the secondary battery, and lithium is easily precipitated during the cycle, resulting in reduced cycle performance of the secondary battery. By regulating the composition of the electrolyte and the mass percentage of the chain carboxylic acid ester compound within the scope of this application, the electrolyte has high conductivity and low viscosity, which can accelerate the transmission speed of lithium ions, further reduce the electrochemical polarization and concentration polarization of the secondary battery, and improve the cycle performance while taking into account the high kinetic performance of the secondary battery.

[0031] This application optimizes the electrochemical system by combining the structural design of the positive and negative electrode tabs, the coating weights of the positive and negative electrode active material layers, and the composition and content of the electrolyte. This allows for improved cycling performance while simultaneously increasing the charging speed of the secondary battery and maintaining a low charging temperature rise, thereby meeting the fast-charging kinetic requirements of the secondary battery. This application also allows for the control of the mass percentage of the chain carboxylate compound by regulating the amount of the chain carboxylate compound added to the electrolyte.

[0032] The secondary battery of the present application can be used under fast charging conditions, specifically, can be used at a charging rate of 5C to 15C. For example, the charging rate of the secondary battery is 5C, 8C, 10C, 12C, 15C or a range consisting of any two values ​​therein.

[0033] In some embodiments of the present application, 6.49 mg / cm 2 ≤W z ≤11.69 mg / cm 2 For example, W z 6.49 mg / cm 2 , 7.00mg / cm 2 , 7.50mg / cm 2 、8.00mg / cm 2 、8.50mg / cm 2 , 9.00mg / cm 2 , 9.50mg / cm 2 、10.00mg / cm2 、10.50mg / cm 2 、11.00mg / cm 2 、11.69mg / cm 2 Or a range consisting of any two of these values. This application, by regulating the coating weight of the positive electrode active material layer within the scope of this application, while taking into account the processing performance and energy density of the secondary battery, shortens the transmission distance of lithium ions and electrons on the positive electrode sheet, which is beneficial to reducing the ohmic polarization and concentration polarization of the secondary battery, thereby reducing the impedance of the secondary battery and making the secondary battery have good cycle performance.

[0034] In some embodiments of the present application, an N1 layer of positive electrode sheet is provided between two adjacent positive electrode tabs, and an N2 layer of negative electrode sheet is provided between two adjacent negative electrode tabs, and N1 and N2 are each independently selected from 0, 1, 2, or 3. As shown in FIG1 , in the wound electrode assembly, two adjacent positive electrode tabs or two adjacent negative electrode tabs are distributed on different layers. From the top down in the figure, no positive electrode sheet 10 is provided between two adjacent positive electrode tabs 12, and no negative electrode sheet 20 is provided between two adjacent negative electrode tabs 22. As shown in FIG2 , in the wound electrode assembly, two adjacent positive electrode tabs or two adjacent negative electrode tabs are distributed on different layers. From the top down in the figure, one layer of positive electrode sheet 10 and two layers of positive electrode sheet 10 are provided between two adjacent positive electrode tabs 12, respectively, and zero layer of negative electrode sheet 20 and three layers of negative electrode sheet 20 are provided between two adjacent negative electrode tabs 22, respectively. Through the above-mentioned configuration, the present application has a sufficient number of positive and negative pole pieces, so that there are multiple current channels on the positive and negative pole pieces, thereby reducing the internal resistance of the secondary battery, and the voltage polarization of the secondary battery during high-rate fast charging is small, the charging temperature rise is reduced, and the charging time is shortened, so that the secondary battery has good dynamic performance and cycle performance. It can be understood that by adjusting N1 and N2 to 0, more current channels can be provided on the positive and negative pole pieces, which can further reduce the internal resistance of the secondary battery, further reduce the charging temperature rise of the fast-charged secondary battery, and further shorten the charging time, thereby further improving the dynamic performance of the fast-charged secondary battery while taking into account the cycle performance and mechanical reliability. However, this will reduce the energy density of the secondary battery to a certain extent; adjusting N1 and N2 to 1, 2, or 3 will reduce the number of pole pieces, increase the internal resistance to a certain extent, but can increase the battery energy density.

[0035] In one embodiment of the present application, an N1 layer of positive electrode sheet is provided between two adjacent positive electrode tabs, and an N2 layer of negative electrode sheet is provided between two adjacent negative electrode tabs, and N1 and N2 are each independently selected from 0. As shown in FIG1 , in the wound electrode assembly, from top to bottom in the figure, no positive electrode sheet 10 is provided between two adjacent positive electrode tabs 12, and no negative electrode sheet 20 is provided between two adjacent negative electrode tabs 22. By regulating N1 and N2 to 0, it is possible to provide positive electrode tabs and negative electrode tabs on each layer of positive electrode sheet and negative electrode sheet in the secondary battery, thereby providing more current channels on the positive electrode sheet and negative electrode sheet, further reducing the internal resistance of the secondary battery, further reducing the charging temperature rise of the secondary battery, and further shortening the charging time, thereby further improving its kinetic performance while taking into account the secondary cycle performance. In the present application, N1 layers of positive electrode sheets are arranged between two adjacent positive electrode tabs, which means that the number of layers of positive electrode sheets with double-sided positive electrode active material layers between two adjacent positive electrode tabs is N1 layers; N2 layers of negative electrode sheets are arranged between two adjacent negative electrode tabs, which means that the number of layers of negative electrode sheets with double-sided negative electrode active material layers between two adjacent negative electrode tabs is N2 layers.

[0036] In some embodiments of the present application, the chain carboxylate compound includes at least one of methyl formate, methyl acetate, ethyl formate, ethyl acetate, propyl acetate, ethyl propionate, methyl propionate, n-propyl propionate, isopropyl propionate, n-butyl propionate, isobutyl propionate, n-pentyl propionate, isopentyl propionate, ethyl butyrate, n-propyl butyrate, propyl isobutyrate, n-pentyl butyrate, n-pentyl isobutyrate, n-butyl butyrate, isobutyl isobutyrate, and n-pentyl valerate. Preferably, the chain carboxylate compound includes at least one of methyl formate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, or ethyl butyrate. By selecting the above-mentioned types of chain carboxylate compounds, the obtained electrolyte has high conductivity and low viscosity, which is conducive to the rapid transmission of lithium ions, reduces the electrochemical polarization and concentration polarization of the secondary battery, reduces the charging temperature rise and shortens the charging time during fast charging of the secondary battery, and has good dynamic performance and cycle performance.

[0037] In some embodiments of the present application, the organic solvent further comprises at least one of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, γ-butyrolactone, or tetrahydrofuran, and the mass percentage of the organic solvent is 60% to 80% based on the mass of the electrolyte. For example, the mass percentage of the organic solvent is 60%, 65%, 70%, 75%, 80%, or a range consisting of any two of these values. By regulating the type and mass percentage of the organic solvent within the scope of the present application, it is beneficial to improve the solubility of the additive and the lithium salt, while taking into account the kinetic performance of the secondary battery and improving the stability of the electrolyte, thereby improving the kinetic performance and cycle performance of the secondary battery. The present application can regulate the mass percentage of the organic solvent by regulating the amount of the organic solvent added to the electrolyte. The mass percentage of the non-chain carboxylic acid ester compound in the organic solvent = the mass percentage of the organic solvent - the mass percentage of the chain carboxylic acid ester compound.

[0038] In some embodiments of the present application, the mass percentage of the lithium salt is 10% to 20% based on the mass of the electrolyte. For example, the mass percentage of the lithium salt is 10%, 12%, 14%, 16%, 18%, 20% or a range consisting of any two of these values. By regulating the mass percentage of the lithium salt within the above range, the lithium salt has a higher solubility in the electrolyte, so that the electrolyte has a higher electrical conductivity, thereby improving the kinetic performance and cycle performance of the secondary battery. The present application can regulate the mass percentage of the lithium salt by regulating the amount of lithium salt added to the electrolyte.

[0039] In some embodiments of the present application, the lithium salt includes at least one of lithium hexafluorophosphate, lithium difluorophosphate, lithium tetrafluoroborate, lithium hexafluoroarsenate, lithium perchlorate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium bis(oxalatoborate), or lithium difluorooxalatoborate. The use of the above-mentioned lithium salts can provide an electrolyte with higher conductivity, thereby improving the kinetic and cycling performance of the secondary battery.

[0040] In some embodiments of the present application, the additive includes at least one of succinonitrile, glutaronitrile, pimelonitrile, 1,2-bis(2-cyanoethoxy)ethane, 1,2-bis(2-cyanoethoxy)propane or 1,2,3-tris(2-cyanoethoxy)propane, and the mass percentage of the additive is 2% to 10% based on the mass of the electrolyte. For example, the mass percentage of the additive is 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10% or a range consisting of any two values ​​therein. By regulating the type and mass percentage of the additive within the scope of this application, the cyano group in the nitrile compound can be complexed with the transition metal element ions in the positive electrode sheet to form a CEI film on the surface of the positive electrode sheet, thereby improving the structural stability of the positive electrode sheet and reducing the side reaction between the positive electrode active material and the electrolyte, thereby improving the high temperature safety performance of the secondary battery. The present application can regulate the mass percentage of the additive by regulating the amount of the additive added to the electrolyte.

[0041] The present application has no particular restrictions on the positive electrode current collector, as long as the purpose of the present application can be achieved. For example, the positive electrode current collector may include aluminum foil, aluminum alloy foil or a composite current collector (such as an aluminum-carbon composite current collector). The positive electrode active material layer of the present application includes a positive electrode active material. The present application has no particular restrictions on the type of positive electrode active material, as long as the purpose of the present application can be achieved. For example, the positive electrode active material may include at least one of lithium nickel cobalt manganese oxide (NCM811, NCM622, NCM523, NCM111), lithium nickel cobalt aluminum oxide, lithium iron phosphate, lithium-rich manganese-based material, lithium cobalt oxide (LiCoO2), lithium manganese oxide, lithium manganese iron phosphate or lithium titanate. In the present application, the positive electrode active material may also include non-metallic elements, for example, non-metallic elements include at least one of fluorine, phosphorus, boron, chlorine, silicon or sulfur. In the present application, there is no particular restriction on the thickness of the positive electrode current collector and the positive electrode active material layer, as long as the purpose of the present application can be achieved. For example, the thickness of the positive electrode current collector is 5 μm to 20 μm, preferably 6 μm to 18 μm. The thickness of the single-sided positive electrode material layer is 30 μm to 120 μm. In the present application, the positive electrode active material layer may further include a conductive agent and a binder. The present application does not particularly limit the type of binder in the positive electrode active material layer, as long as the purpose of the present application can be achieved. For example, the binder may include but is not limited to at least one of polyvinylidene fluoride, vinylidene fluoride-hexafluoropropylene copolymer, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate, polyvinyl pyrrolidone, polyvinyl ether, polymethyl methacrylate, polytetrafluoroethylene or polyhexafluoropropylene. The present application does not particularly limit the type of conductive agent in the positive electrode active material layer, as long as the purpose of the present application can be achieved. For example, the conductive agent may include but is not limited to at least one of conductive carbon black (Super P), carbon nanotubes (CNTs), carbon fibers, flake graphite, Ketjen black, graphene, metal materials or conductive polymers. The above-mentioned carbon nanotubes may include but are not limited to single-walled carbon nanotubes and / or multi-walled carbon nanotubes. The above-mentioned carbon fibers may include but are not limited to vapor grown carbon fibers (VGCF) and / or nano-carbon fibers. The above-mentioned metal materials may include but are not limited to metal powders and / or metal fibers. Specifically, the metal may include but is not limited to at least one of copper, nickel, aluminum or silver. The above-mentioned conductive polymers may include but are not limited to at least one of polyphenylene derivatives, polyaniline, polythiophene, polyacetylene or polypyrrole. The present application does not particularly limit the mass ratio of the positive electrode active material, the conductive agent and the binder in the positive electrode active material layer. Those skilled in the art can select according to actual needs as long as the purpose of the present application can be achieved.

[0042] This application places no particular restrictions on the negative electrode current collector, as long as the objectives of this application can be achieved. For example, the negative electrode current collector can include copper foil, copper alloy foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, or composite current collectors (such as lithium-copper composite current collectors, carbon-copper composite current collectors, nickel-copper composite current collectors, titanium-copper composite current collectors, etc.). The negative electrode active material layer of this application contains negative electrode active materials. This application places no particular restrictions on the types of negative electrode active materials, as long as the objectives of this application can be achieved. For example, the negative electrode active materials can include natural graphite, artificial graphite, mesocarbon microbeads (MCMB), hard carbon, soft carbon, silicon, silicon-carbon composites, SiO x (0 < x < 2), Li-Sn alloy, Li-Sn-O alloy, Sn, SnO, SnO2, lithium titanate with a spinel structure Li4Ti5O 12 , Li-Al alloy, or at least one of metallic lithium. In this application, there are no particular restrictions on the thickness of the negative electrode current collector and the negative electrode material layer, as long as the objectives of this application can be achieved. For example, the thickness of the negative electrode current collector is 4 μm to 20 μm, and the thickness of the negative electrode active material layer is 30 μm to 130 μm. Optionally, the negative electrode active material layer can also include a conductive agent and a binder. This application places no particular restrictions on the types of conductive agents in the negative electrode active material layer, as long as the objectives of this application can be achieved. For example, the conductive agent can be of the same type as the conductive agent in the above-mentioned positive electrode active material layer. This application places no particular restrictions on the types of binders in the negative electrode active material layer, as long as the objectives of this application can be achieved. For example, the binder can be of the same type as the binder in the above-mentioned positive electrode active material layer. This application places no particular restrictions on the mass ratio of the negative electrode active material, conductive agent, and binder in the negative electrode active material layer, as long as the objectives of this application can be achieved.

[0043] There are no particular restrictions on the separator in the secondary battery of this application, as long as the objectives of this application can be achieved. For example, the separator includes at least one of polyethylene (PE), polypropylene (PP), polyethylene terephthalate (PET), polyimide (PI), or aramid. For example, polyethylene includes at least one selected from high-density polyethylene, low-density polyethylene, and ultra-high molecular weight polyethylene. The separator of this application can have a porous structure. This application places no particular restrictions on the size of the pore diameter of the porous structure of the separator, as long as the objectives of this application can be achieved. For example, the size of the pore diameter can be 0.01 μm to 1 μm. This application places no particular restrictions on the thickness of the separator, as long as the objectives of this application can be achieved. For example, the thickness of the separator can be 5 μm to 500 μm.

[0044] The secondary battery of this application also includes a packaging bag for accommodating the positive electrode sheet, the negative electrode sheet, the separator, and the electrolyte, as well as other components of the secondary battery known in the art. This application does not limit these other components. This application does not specifically limit the packaging bag and can be any packaging bag known in the art, as long as it can achieve the purpose of this application.

[0045] The secondary battery of the present application is not particularly limited and may include any device that undergoes an electrochemical reaction. In one embodiment of the present application, the electrochemical device may include, but is not limited to, a lithium ion secondary battery (lithium ion battery), a lithium polymer secondary battery, or a lithium ion polymer secondary battery.

[0046] The present application does not impose any particular restrictions on the method for preparing the positive electrode sheet, as long as the purpose of the present application can be achieved. For example, the method for preparing the positive electrode sheet includes but is not limited to the following steps: (1) preparing a positive electrode slurry; (2) coating the positive electrode slurry on one surface of the positive electrode main region of the positive electrode current collector, and after drying, forming a positive electrode active material layer on one surface of the positive electrode main region of the positive electrode current collector; (3) coating the positive electrode slurry on the other surface of the positive electrode main region of the positive electrode current collector, and after drying, forming a positive electrode active material layer on each of the two surfaces of the positive electrode main region of the positive electrode current collector; (4) die-cutting the positive electrode tab area of ​​the positive electrode current collector after cold pressing, so that the positive electrode current collector extends integrally to form multiple positive electrode tabs; (5) cutting the sheet to obtain the positive electrode sheet. The present application does not impose any particular restrictions on the content and type of each component in the positive electrode slurry in the above step (2). Those skilled in the art can select according to actual conditions, as long as the purpose of the present application can be achieved. The present application has no particular restrictions on the solid content of the positive electrode slurry in the above step (1), as long as the coating weight of the obtained positive electrode active material layer is within the scope of the present application and the purpose of the present application can be achieved. The present application has no particular restrictions on the time and temperature of the drying in the above steps (2) and (4), as long as the purpose of the present application can be achieved. The present application has no particular restrictions on the process parameters of the cold pressing in the above step (4), as long as the purpose of the present application can be achieved.

[0047] The present application does not impose any particular restrictions on the method for preparing the negative electrode sheet, as long as the purpose of the present application can be achieved. For example, the method for preparing the negative electrode sheet includes but is not limited to the following steps: (1) preparing a negative electrode slurry; (2) coating the negative electrode slurry on one surface of the negative electrode main region of the negative electrode current collector, and after drying, forming a negative electrode active material layer on one surface of the negative electrode main region of the negative electrode current collector; (3) coating the negative electrode slurry on the other surface of the negative electrode main region of the negative electrode current collector, and after drying, forming a negative electrode active material layer on each of the two surfaces of the negative electrode main region of the negative electrode current collector; (4) die-cutting the negative electrode tab region of the negative electrode current collector after cold pressing, so that the negative electrode current collector extends integrally to form multiple negative electrode tabs; (5) slitting to obtain the negative electrode sheet. The present application does not impose any particular restrictions on the content and type of each component in the negative electrode slurry in the above step (1). Those skilled in the art can select according to actual conditions, as long as the purpose of the present application can be achieved. The present application has no particular restrictions on the solid content of the negative electrode slurry in step (1) above, as long as the coating weight of the resulting negative electrode active material layer is within the scope of the present application and the purpose of the present application can be achieved. The present application has no particular restrictions on the time and temperature of the drying in steps (2) and (3) above, as long as the purpose of the present application can be achieved. The present application has no particular restrictions on the process parameters of the cold pressing in step (4) above, as long as the purpose of the present application can be achieved.

[0048] This application does not particularly limit the preparation method of the secondary battery. Any preparation method known in the art may be used, as long as the purpose of this application can be achieved. For example, the preparation method of the secondary battery includes, but is not limited to, the following steps: stacking a separator, a positive electrode sheet, a separator, and a negative electrode sheet in sequence, and winding and folding them as needed to obtain a wound electrode assembly; spot welding multiple positive electrode tabs and multiple negative electrode tabs; placing the electrode assembly in a housing; injecting an electrolyte into the housing and sealing it to obtain a secondary battery.

[0049] The second aspect of the present application provides an electric device, which includes the secondary battery according to any one of the aforementioned embodiments. Therefore, the electric device has good performance.

[0050] The electrical device of the present application is not particularly limited and can be any electronic device known in the art. For example, the electronic device can include, but is not limited to, a laptop computer, a pen-type computer, a mobile computer, an electronic book player, a portable phone, a portable fax machine, a portable copier, a portable printer, a headset, a video recorder, an LCD television, a portable cleaner, a portable CD player, a mini-disc, a transceiver, an electronic notepad, a calculator, a memory card, a portable recorder, a radio, a backup power supply, a motor, an automobile, a motorcycle, a power-assisted bicycle, a bicycle, a lighting fixture, a toy, a game console, a clock, a power tool, a flashlight, a camera, a large household battery, and a lithium-ion capacitor.

[0051] Example

[0052] Hereinafter, the embodiments of the present application will be described in more detail with reference to Examples and Comparative Examples. Various tests and evaluations were performed according to the following methods.

[0053] Test methods and equipment:

[0054] Coat Weight Test:

[0055] (1) Coating weight W of the positive electrode active material layer z test:

[0056] The lithium-ion battery was discharged at 0.5C to 3.0V and then disassembled to obtain the positive electrode sheet. The positive electrode sheet was immersed in dimethyl carbonate (DMC) solution for 4 hours and then dried. The area A mm was cut. 2 The positive electrode sheet sample is placed on a balance and weighed, which is recorded as p1. The positive electrode active material layer on the positive electrode sheet is then washed clean, and the positive electrode current collector is placed on a balance and weighed, which is recorded as p2.

[0057] If the positive electrode sheet is coated with a positive electrode active material layer on one side, W z =(p1-p2) / A.

[0058] If it is a positive electrode sheet coated with a positive electrode active material layer on both sides, W z =(p1-p2) / 2A.

[0059] (2) Coating weight W of negative electrode active material layer f test:

[0060] The lithium-ion battery was discharged at 0.5C to 3.0V and then disassembled to obtain the negative electrode sheet. The negative electrode sheet was soaked in DMC solution for 4 hours and then dried. The area B mm was cut. 2 The negative electrode sheet sample is placed on a balance and weighed, which is recorded as q1. Then the negative electrode active material layer on the negative electrode sheet is washed clean, and the negative electrode current collector is placed on a balance and weighed, which is recorded as q2.

[0061] If the negative electrode sheet is coated with a negative electrode active material layer on one side, W f =(q1-q2) / B.

[0062] If it is a negative electrode sheet with negative electrode active material layer coated on both sides, W f =(q1-q2) / 2B.

[0063] Dynamic performance test:

[0064] The lithium-ion batteries in each embodiment and comparative example were subjected to a dynamic performance test at a charge rate of 10C, and the specific steps are as follows:

[0065] The test temperature was adjusted to a constant temperature of 25°C, and the temperature sensing line of the multi-channel thermometer was placed at the center of the surface of the lithium-ion battery. The following steps were performed: (1) 10C constant current charging to 4.20V; (2) 8C constant current charging to 4.35V; (3) 5C constant current charging to 4.45V; (4) 4.45V constant voltage charging to 0.05C; (5) standing for 30 minutes; (6) 1C constant current discharge to 3.0V; (7) standing for 30 minutes; end.

[0066] Charging speed: the time from step (1) to step (4) in step (1);

[0067] Charging temperature rise: the difference between the maximum temperature from step (1) to step (2) in step (1) recorded by the temperature sensing line on the surface of the lithium-ion battery and the room temperature.

[0068] The kinetic performance is characterized by charging speed, charging temperature rise and lithium-ion battery impedance. Among them, the lower the lithium-ion battery impedance, the shorter the charging time and the smaller the charging temperature rise, the better the kinetic performance.

[0069] Cycle performance test:

[0070] The lithium-ion batteries in the embodiments and comparative examples were subjected to a cycle performance test at a charge rate of 10C, and the specific steps were as follows:

[0071] Adjust the test temperature to 25℃ and start the test: (1) 10C constant current charging to 4.20V; (2) 8C constant current charging to 4.35V; (3) 6C constant current charging to 4.40V; (4) 4.40V constant voltage charging to 0.05C; (5) stand for 5 minutes; (6) 1C constant current discharge to 3.0V; (7) stand for 5 minutes; (8) cycle steps (1) to (7) for 1000 times (cls); end;

[0072] Capacity retention (%) = discharge capacity after 1000 cycles / first cycle discharge capacity × 100%.

[0073] Example 1-1

[0074] <Preparation of positive electrode sheet>

[0075] The positive electrode active material is lithium cobalt oxide, the positive electrode conductive agent is superconducting carbon (Super P), and the positive electrode binder is polyvinylidene fluoride (PVDF, Mw = 70 × 10 5 ) are mixed in a mass ratio of 95:2.5:2.5, N-methylpyrrolidone (NMP) is added as a solvent, and stirred in a vacuum mixer until a solid content of 75wt% and a uniform positive electrode slurry is obtained. The positive electrode slurry is evenly coated on the positive electrode main area of ​​one surface of a positive electrode current collector aluminum foil with a thickness of 13μm, and dried at 95°C to obtain a positive electrode sheet with a single-sided positive electrode active material layer. Thereafter, the above steps are repeated on the positive electrode main area of ​​the other surface of the aluminum foil to obtain a positive electrode sheet with a double-sided positive electrode active material layer. The sheet is then cold pressed, die-cut, and slit, and then dried at 85°C under vacuum for 4 hours to obtain a positive electrode sheet with a specification of 60mm×1580mm for use. The single layer thickness of the positive electrode active material layer is 38.5μm, and the thickness of the positive electrode sheet is 90μm. The positive electrode tab area of ​​the positive electrode current collector is formed into 20 positive electrode tabs by die-cutting (the structure is shown in FIG4 , but is not limited to FIG4 ). The coating weight of the positive electrode active material layer is W z 9.08 mg / cm 2 .

[0076] <Preparation of negative electrode sheet>

[0077] The negative electrode active material artificial graphite, negative electrode conductive agent Super P, stabilizer sodium carboxymethyl cellulose (CMC-Na, Mw = 7 × 10 5 ), negative electrode binder styrene-butadiene rubber (SBR, Mw = 50 × 10 5) were mixed in a mass ratio of 96:1.0:1.5:1.5, then deionized water was added as a solvent and stirred in a vacuum mixer until a solid content of 51 wt% and a uniform negative electrode slurry was obtained. The negative electrode slurry was evenly coated on the negative electrode main area of ​​one surface of a 10 μm thick negative electrode current collector copper foil and dried at 85°C to obtain a negative electrode sheet coated with a negative electrode active material layer on one side. The above steps were then repeated on the negative electrode main area of ​​the other surface of the copper foil to obtain a negative electrode sheet coated with a negative electrode active material layer on both sides. The sheet was then cold pressed, die-cut, and slit, and then dried at 110°C under vacuum for 4 hours to obtain a negative electrode sheet measuring 62 mm x 1600 mm for later use. The thickness of the negative electrode active material layer was 58.5 μm, and the thickness of the negative electrode sheet was 127 μm. The negative electrode tab area of ​​the negative electrode current collector is integrally formed by die-cutting (the structure is shown in FIG5 , but is not limited to FIG5 ) to form 20 negative electrode tabs, and the coating weight of the negative electrode active material layer is W f 4.54 mg / cm 2 .

[0078] <Preparation of Electrolyte>

[0079] In a dry argon atmosphere glove box, an electrolyte solution was prepared using a linear carboxylate compound, n-propyl propionate, and non-linear carboxylate compounds, ethylene carbonate and diethyl carbonate, as organic solvents. Lithium hexafluorophosphate (LiPF6) and the additive succinonitrile were dissolved and mixed uniformly in the organic solvent. Based on the mass of the electrolyte, the weight percentage of n-propyl propionate was 40%, the weight percentage of the organic solvent was 80%, the weight percentage of LiPF6 was 17%, and the weight percentage of succinonitrile was 3%. The weight percentage ratio of ethylene carbonate to diethyl carbonate was 1:1.

[0080] <Preparation of Separator>

[0081] A polypropylene film with a thickness of 5 μm was selected as the isolation membrane.

[0082] <Preparation of lithium-ion batteries>

[0083] The separator, positive electrode sheet, separator, and negative electrode sheet are stacked in order, with the separator placed between the positive and negative electrode sheets to act as an insulator, and then wound to form an electrode assembly. The positive electrode tabs are spot welded out with aluminum tabs, and the negative electrode tabs are spot welded out with nickel tabs. After winding, each layer of positive electrode sheet with positive tabs in the electrode assembly has a positive electrode tab, and each layer of negative electrode sheet with negative tabs has a negative electrode tab. Between two adjacent positive electrode tabs, there are N1=0 layers of positive electrode sheets, and between two adjacent negative electrode tabs, there are N2=0 layers of negative electrode sheets (see FIG1 for the arrangement of the positive and negative tabs, but not limited to FIG1).

[0084] The electrode assembly is placed in an aluminum-plastic film shell, and after drying, the electrolyte is injected. The lithium-ion battery is obtained through vacuum packaging, standing, formation, capacity, degassing, and trimming processes.

[0085] Example 1-2 to Example 1-12

[0086] The preparation parameters were adjusted according to Table 1, and the remainder was the same as Example 1-1. When the content of the chain carboxylate compound in the electrolyte was changed, the content of the organic solvent remained unchanged, and the content of the non-chain carboxylate compounds ethylene carbonate and diethyl carbonate in the organic solvent was changed accordingly, wherein the mass percentage ratio of ethylene carbonate to diethyl carbonate remained unchanged at 1:1.

[0087] Examples 1-13

[0088] <Preparation of positive electrode sheet>

[0089] Except that the positive electrode tab region of the positive electrode current collector is integrally extended to form 10 positive electrode tabs, the rest is the same as Example 1-1.

[0090] <Preparation of negative electrode sheet>

[0091] Except that the negative electrode tab region of the negative electrode current collector is integrally extended to form 10 negative electrode tabs, the rest is the same as Example 1-1.

[0092] <Preparation of lithium-ion batteries>

[0093] Except that N1 = 1 layer of positive electrode sheets is provided between two adjacent positive electrode tabs and N2 = 1 layer of negative electrode sheets is provided between two adjacent negative electrode tabs, the rest is the same as Example 1-1.

[0094] <Preparation of Separator> and <Preparation of Electrolyte> were the same as those in Example 1-1.

[0095] Examples 1-14

[0096] <Preparation of positive electrode sheet>

[0097] Except that the positive electrode tab region of the positive electrode current collector is integrally extended to form 6 positive electrode tabs, the rest is the same as Example 1-1.

[0098] <Preparation of negative electrode sheet>

[0099] Except that the negative electrode tab region of the negative electrode current collector is integrally extended to form 6 negative electrode tabs, the rest is the same as Example 1-1.

[0100] <Preparation of lithium-ion batteries>

[0101] Except that N1 = 2 layers of positive electrode sheets are provided between two adjacent positive electrode tabs and N2 = 2 layers of negative electrode sheets are provided between two adjacent negative electrode tabs, the rest is the same as Example 1-1.

[0102] <Preparation of Separator> and <Preparation of Electrolyte> were the same as those in Example 1-1.

[0103] Example 2-1 to Example 2-8

[0104] Except for adjusting the relevant preparation parameters according to Table 2, the rest is the same as Example 1-1. Among them, when the type of non-chain carboxylate compound in the organic solvent changes, the content ratio between the non-chain carboxylate compounds does not change. When the content of the organic solvent changes, the content of the chain carboxylate compound in the organic solvent remains unchanged, and the content of the non-chain carboxylate compound in the organic solvent changes accordingly, and the mass ratio of the two substances in the non-chain carboxylate compound remains unchanged at 1:1.

[0105] Examples 2-9

[0106] The preparation process was the same as Example 1-1, except that no additives were added in the preparation of the electrolyte solution and the relevant preparation parameters were adjusted according to Table 2. When the content of the organic solvent was changed, the content of the chain carboxylate compound in the organic solvent remained unchanged, and the content of the non-chain carboxylate compounds ethylene carbonate and diethyl carbonate in the organic solvent changed accordingly. The weight percentage ratio of ethylene carbonate to diethyl carbonate remained unchanged at 1:1.

[0107] Example 2-10

[0108] Except for adjusting the relevant preparation parameters according to Table 2, the rest is the same as Example 1-1.

[0109] Comparative Examples 1 to 4

[0110] Except for adjusting the relevant preparation parameters according to Table 1, the rest is the same as Example 1-1.

[0111] Comparative Example 5

[0112] Except that the following preparation steps were adopted for <Preparation of Electrolyte>, the rest were the same as Example 1-1.

[0113] <Preparation of Electrolyte>

[0114] In a dry argon atmosphere glove box, the non-chain carboxylic acid ester compounds ethylene carbonate and diethyl carbonate were used as organic solvents. Lithium hexafluorophosphate (LiPF6) and the additive succinonitrile were dissolved and mixed uniformly to form an electrolyte. Based on the mass of the electrolyte, the weight percentage of the organic solvent was 80%, the weight percentage of LiPF6 was 17%, and the weight percentage of succinonitrile was 3%. The weight percentage ratio of ethylene carbonate to diethyl carbonate was 1:1.

[0115] Comparative Example 6 to Comparative Example 7

[0116] The preparation parameters were adjusted according to Table 1, and the remainder was the same as Example 1-1. When the content of the chain carboxylate compound in the electrolyte was changed, the content of the organic solvent remained unchanged, and the content of the non-chain carboxylate compounds ethylene carbonate and diethyl carbonate in the organic solvent was changed accordingly, wherein the mass percentage ratio of ethylene carbonate to diethyl carbonate remained unchanged at 1:1.

[0117] Comparative Example 8

[0118] Except that the following preparation steps are used for <Preparation of Positive Electrode Sheet>, <Preparation of Negative Electrode Sheet>, and <Preparation of Lithium-ion Battery>, the rest are the same as Example 1-1.

[0119] <Preparation of positive electrode sheet>

[0120] The positive electrode active material is lithium cobalt oxide, the positive electrode conductive agent is superconducting carbon (Super P), and the positive electrode binder is polyvinylidene fluoride (PVDF, Mw = 70 × 10 5 ) are mixed in a mass ratio of 96:2:2, N-methylpyrrolidone (NMP) is added as a solvent, and stirred under the action of a vacuum mixer to a positive electrode slurry with a solid content of 75wt% and a uniform system. The positive electrode slurry is evenly coated on one surface of a positive electrode current collector aluminum foil with a thickness of 13μm, and dried at 95°C to obtain a positive electrode sheet with a single-sided positive electrode active material layer. Thereafter, the above steps are repeated on the other surface of the aluminum foil to obtain a positive electrode sheet with a double-sided positive electrode active material layer. It is then cold pressed, cut into pieces, and slit, and then dried at 85°C under vacuum conditions for 4h. A positive electrode aluminum tab is welded on the surface of the positive electrode collector to obtain a positive electrode sheet with a specification of 60mm×1580mm for standby use. Among them, the single layer thickness of the positive electrode active material layer is 38.5μm, and the thickness of the positive electrode sheet is 90μm. The coating weight W of the positive electrode active material layer z 9.08 mg / cm 2 .

[0121] <Preparation of negative electrode sheet>

[0122] The negative electrode active material artificial graphite, negative electrode conductive agent Super P, stabilizer sodium carboxymethyl cellulose (CMC-Na, Mw = 7 × 10 5 ), negative electrode binder styrene-butadiene rubber (SBR, Mw = 50 × 10 5 ) are mixed in a mass ratio of 96.5:1.0:1.0:1.5, and then deionized water is added as a solvent, and stirred under the action of a vacuum mixer until the solid content is 51wt% and the system is uniform. The negative electrode slurry is evenly coated on one surface of a negative electrode current collector copper foil with a thickness of 10μm, and dried at 85°C to obtain a negative electrode sheet with a single-sided negative electrode active material layer. Thereafter, the above steps are repeated on the other surface of the copper foil to obtain a negative electrode sheet with a double-sided negative electrode active material layer. It is then cold pressed, cut into pieces, and striped. After stripping, it is dried at 110°C under vacuum conditions for 4h, and a negative electrode tab nickel tab is welded on the surface of the negative electrode collector to obtain a negative electrode sheet with a specification of 62mm×1600mm for standby use. Among them, the single layer thickness of the negative electrode active material layer is 58.5μm, and the thickness of the negative electrode sheet is 127μm. The coating weight W of the negative electrode active material layer f 4.54 mg / cm 2 .

[0123] <Preparation of lithium-ion batteries>

[0124] The separator, positive electrode sheet, separator, and negative electrode sheet are stacked in sequence, with the separator positioned between the positive and negative electrodes to provide insulation. The electrode assembly is then wound to form a complete package. The assembly is then placed in an aluminum-plastic film casing, dried, and then filled with electrolyte. The lithium-ion battery is then produced through vacuum packaging, resting, formation, capacity measurement, degassing, and trimming.

[0125] Comparative Example 9

[0126] Except for the preparation of the electrolyte, the rest is the same as that of Comparative Example 8.

[0127] Comparative Example 10

[0128] Except for adjusting the relevant preparation parameters according to Table 1, the rest are the same as Comparative Example 5.

[0129] Comparative Example 11

[0130] Except for adjusting the relevant preparation parameters according to Table 1, the rest are the same as Comparative Example 9.

[0131] The preparation parameters and performance parameters of each embodiment and comparative example are shown in Tables 1 and 2.

[0132] Table 1

[0133] Note: “ / ” in Table 1 indicates no corresponding parameter.

[0134] It can be seen from Examples 1-1 to 1-14 and Comparative Examples 1 to 11 that the lithium-ion battery of the embodiment of the present application has a multi-electrode structure by providing a positive electrode current collector integrally extending to form a plurality of positive electrode tabs and a negative electrode current collector integrally extending to form a plurality of negative electrode tabs. At the same time, the coating weight W of the positive electrode active material layer is regulated. z The coating weight W of the negative electrode active material layer f The ratio W z / W f and W f The value of is within the scope of this application, and a chain carboxylate compound is added to the electrolyte to regulate the mass percentage of the chain carboxylate compound within the scope of this application. The lithium-ion battery has lower impedance, shorter charging time (i.e., higher charging speed), lower charging temperature rise and higher capacity retention rate at a charging rate of 10C, indicating that the lithium-ion battery in the embodiment of the present application has better kinetic performance and cycle performance during fast charging.

[0135] In the lithium ion batteries of Comparative Examples 1 and 2, the coating weight W of the negative electrode active material layer is f Not within the scope of this application, the lithium ion batteries in Comparative Examples 3 and 4, the coating weight W of the positive electrode active material layer z The coating weight W of the negative electrode active material layer f The ratio W z / W f The coating weight W of the positive electrode active material layer of Comparative Example 1 is not within the scope of this application. z The coating weight W of the negative electrode active material layer f The obtained lithium-ion battery has a faster charging speed and lower impedance, but because the coating weight of the positive electrode active material layer and the negative electrode active material layer is too low, the cost of accurately controlling the coating weight in actual industrial production is too high, and the qualified rate of the lithium-ion battery obtained in large-scale production is too low and the energy density of the obtained lithium-ion battery is too low, which cannot meet the needs of actual production and is not suitable for industrial production applications. The lithium-ion battery in Comparative Example 2 has a higher impedance, a longer charging time (that is, a lower charging speed), a higher charging temperature rise and a lower capacity retention rate at a charging rate of 10C, indicating that the lithium-ion battery has poor kinetic performance and cycle performance during high-rate fast charging. The coating weight W of the positive electrode active material layer of Comparative Example 3 is zThe coating weight of the negative electrode active material layer is too large relative to the coating weight of the positive electrode active material layer. When the potential of the secondary battery is reached, the lithium removal rate of the positive electrode increases significantly, resulting in a high actual potential of the positive electrode and easy destruction of the structure. The positive electrode decays rapidly, resulting in a very poor cycle life of the secondary battery. The coating weight W of the positive electrode active material layer in Comparative Example 4 is z Too large and with the coating weight W of the negative electrode active material layer f The ratio W z / W f Too large, resulting in a mismatch between the capacity of the positive electrode sheet and the negative electrode sheet. When the lithium-ion battery is fast charged, the lithium ions in the positive electrode sheet cannot be released in time, and the lithium ions cannot be embedded in the negative electrode sheet in time, which cannot meet the charging speed requirements during fast charging, easily leading to the occurrence of lithium precipitation, low capacity retention rate, and poor cycle performance of the lithium-ion battery. The electrolyte in Comparative Example 5 does not add chain carboxylic acid ester compounds, and the mass percentage of chain carboxylic acid ester compounds in Comparative Examples 6 and 7 is not within the scope of this application. The lithium-ion batteries in Comparative Examples 5 and 6 have higher impedance, longer charging time (that is, lower charging speed), higher charging temperature rise and lower capacity retention rate at a charging rate of 10C, indicating that the lithium-ion battery has poor kinetic performance and cycle performance during fast charging. In Comparative Example 7, due to the excessively high mass percentage of chain carboxylic acid ester compounds, the battery system is too active, and side reactions are prone to occur during the cycle, resulting in a decrease in capacity retention rate, and the cycle performance of the lithium-ion battery is poor. The lithium-ion battery in Comparative Example 8 has an embedded single-pole structure rather than the multi-pole structure of the present application. The resulting lithium-ion battery has a higher impedance, a longer charging time (i.e., a lower charging speed), a higher charging temperature rise, and a lower capacity retention rate at a charging rate of 10C, indicating that the lithium-ion battery has poor kinetic performance and cycle performance during fast charging. The electrolyte in Comparative Example 9 does not add a chain carboxylate compound, and the lithium-ion battery has an embedded single-pole structure rather than the multi-pole structure of the present application. The resulting lithium-ion battery has a higher impedance, a longer charging time (i.e., a lower charging speed), a higher charging temperature rise, and a lower capacity retention rate at a charging rate of 10C, indicating that the lithium-ion battery has poor kinetic performance and cycle performance during fast charging. For the lithium-ion battery in Comparative Example 10, the coating weight W of the positive electrode active material layer is 200W. z The coating weight W of the negative electrode active material layer f The ratio W z / W fIt is not within the scope of this application that the electrolyte does not contain chain carboxylic acid ester compounds. The resulting lithium ion battery has higher impedance, longer charging time (i.e., lower charging speed), higher charging temperature rise, and lower capacity retention at a charging rate of 10C, indicating that the lithium ion battery has poor kinetic performance and cycle performance during fast charging. z The coating weight W of the negative electrode active material layer f The ratio W z / W f It is not within the scope of this application. The electrolyte does not add chain carboxylate compounds, and the lithium-ion battery has an embedded single-pole structure rather than the multi-pole structure of this application. The resulting lithium-ion battery has higher impedance, longer charging time (i.e., lower charging speed), higher charging temperature rise and lower capacity retention rate at a charging rate of 10C, indicating that the lithium-ion battery has poor kinetic performance and cycle performance during fast charging.

[0136] The coating weight W of the positive electrode active material layer z It usually affects the dynamic performance and cycle performance of lithium-ion batteries during high-rate fast charging. z The lithium-ion battery within the scope of this application has low impedance, short charging time (i.e., high charging speed), low charging temperature rise, and high capacity retention rate at a charging rate of 10C, indicating that the lithium-ion battery has good kinetic performance and cycle performance during fast charging. The coating weight W of the positive electrode active material layer in Examples 1-6 is z The coating weight of the negative electrode active material layer is relatively low, and the coating weight of the positive electrode active material layer is relatively small. When the potential of the secondary battery is reached, the delithiation rate of the positive electrode increases, which may lead to the occurrence of excessive delithiation of the positive electrode, thereby reducing the capacity retention rate of the lithium-ion battery. Furthermore, although the charging speed of the lithium-ion battery is relatively fast and the impedance is relatively low, the energy density of the lithium-ion battery is relatively low. In actual industrial production, it is difficult to control the coating weight of the positive electrode active material layer. In Examples 1-7, the coating weight W of the positive electrode active material layer is relatively high. zThe coating weight of the negative electrode active material layer is relatively high, and the coating weight of the positive electrode active material layer is quite different from that of the positive electrode active material layer. When the lithium-ion battery is fast charged, the lithium ions in the positive electrode sheet cannot be removed in time, and the lithium ions cannot be embedded in the negative electrode sheet in time, which easily leads to the occurrence of lithium precipitation, thereby reducing the capacity retention rate of the lithium-ion battery. The type of chain carboxylic acid ester compound usually affects the kinetic performance and cycle performance of the lithium-ion battery during high-rate fast charging. It can be seen from Example 1-1, Example 1-11 to Example 1-12 that the lithium-ion battery whose type of chain carboxylic acid ester compound is within the scope of this application has lower impedance, shorter charging time (that is, higher charging speed), lower charging temperature rise and higher capacity retention rate at a charging rate of 10C, indicating that the lithium-ion battery has better kinetic performance during fast charging.

[0137] The values ​​of N1 and N2 generally affect the kinetic performance and cycling performance of lithium-ion batteries during fast charging. As can be seen from Examples 1-1, 1-13, and 1-14, lithium-ion batteries with N1 and N2 values ​​within the ranges of this application exhibit lower impedance, shorter charging times (i.e., higher charging speeds), lower charging temperature rise, and higher capacity retention at a 10C charge rate, demonstrating that lithium-ion batteries exhibit better kinetic performance and cycling performance during fast charging.

[0138] Table 2

[0139] Note: “ / ” in Table 2 indicates no corresponding parameter.

[0140] The type and content of organic solvents generally affect the kinetic performance and cycling performance of lithium-ion batteries during fast charging. As can be seen from Examples 1-1, 2-1, and 2-5, lithium-ion batteries using organic solvents with a type and content within the ranges of this application exhibit lower impedance, shorter charging times (i.e., higher charging speeds), lower charging temperature rise, and higher capacity retention at a 10C charge rate, indicating that lithium-ion batteries have better kinetic performance and cycling performance during fast charging.

[0141] The type and content of lithium salts generally affect the kinetic performance and cycling performance of lithium-ion batteries during fast charging. As can be seen from Examples 1-1, 2-6, and 2-8, lithium-ion batteries using lithium salts with types and contents within the ranges of this application exhibit lower impedance, shorter charging times (i.e., higher charging speeds), lower charging temperature rise, and higher capacity retention at a 10C charge rate, indicating that lithium-ion batteries have better kinetic performance and cycling performance during fast charging.

[0142] The type and content of additives generally affect the kinetic performance and cycling performance of lithium-ion batteries during fast charging. As can be seen from Examples 1-1, 2-7, and 2-10, lithium-ion batteries using additives whose types and contents fall within the ranges of this application exhibit lower impedance, shorter charging times (i.e., higher charging speeds), lower charging temperature rise, and higher capacity retention at a 10C charge rate, indicating that lithium-ion batteries exhibit better kinetic performance and cycling performance during fast charging.

[0143] The terms "comprises," "comprising," or any other variations thereof are intended to cover non-exclusive inclusion such that a process, method, or article that comprises a list of elements includes not only those elements but also other elements not expressly listed or inherent to such process, method, or article.

[0144] Each embodiment in this specification is described in a related manner. The same or similar parts between the embodiments can be referred to each other. Each embodiment focuses on the differences from other embodiments.

[0145] The above description is only a preferred embodiment of the present application and is not intended to limit the present application. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present application shall be included in the scope of protection of the present application.

Claims

1. A secondary battery, which comprises a positive electrode plate, a negative electrode plate and an electrolyte. The positive electrode plate includes a positive current collector and a positive active material layer, and the negative electrode plate includes a negative current collector and a negative active material layer; the coating weight of the positive active material layer is W z , the coating weight of the negative active material layer is W f , W z and W f satisfy the following: 1.6W f ≤ W z ≤ 2.2W f 、3.25mg / cm 2 ≤ W f ≤ 5.84mg / cm 2 ; The positive current collector integrally extends to form a plurality of positive electrode tabs; the negative current collector integrally extends to form a plurality of negative electrode tabs; The electrolyte includes an organic solvent, a lithium salt, and an additive. The organic solvent includes a chain carboxylic acid ester compound. Based on the mass of the electrolyte, the mass percentage of the chain carboxylic acid ester compound is 6% to 56%.

2. The secondary battery according to claim 1, wherein, 6.49 mg / cm 2 ≤W z ≤11.69 mg / cm 2 。 3. The secondary battery according to claim 1, wherein, There are N1 layers of positive electrode sheets disposed between two adjacent positive electrode tabs, and N2 layers of negative electrode sheets disposed between two adjacent negative electrode tabs. N1 and N2 each independently selected from 0, 1, 2, or 3.

4. The secondary battery according to claim 1, wherein, The chain carboxylic acid ester compound includes at least one of methyl formate, methyl acetate, ethyl formate, ethyl acetate, propyl acetate, ethyl propionate, methyl propionate, n-propyl propionate, isopropyl propionate, n-butyl propionate, isobutyl propionate, n-pentyl propionate, isopentyl propionate, ethyl n-butyrate, n-propyl n-butyrate, isopropyl butyrate, n-pentyl n-butyrate, isopentyl n-butyrate, n-butyl n-butyrate, isobutyl isobutyrate, n-pentyl n-pentanoate.

5. The secondary battery according to claim 1, wherein, The organic solvent further includes at least one of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, γ-butyrolactone, or tetrahydrofuran. Based on the mass of the electrolyte, the mass percentage of the organic solvent is 60% to 80%.

6. The secondary battery according to claim 1, wherein, Based on the mass of the electrolyte, the mass percentage of the lithium salt is 10% to 20%.

7. The secondary battery according to claim 1, wherein, The additive includes at least one of succinonitrile, glutaronitrile, pimelonitrile, 1,2-bis(2-cyanoethoxy)ethane, 1,2-bis(2-cyanoethoxy)propane, or 1,2,3-tris(2-cyanoethoxy)propane. Based on the mass of the electrolyte, the mass percentage of the additive is 2% to 10%.

8. The secondary battery according to claim 1, wherein, Satisfies at least one of the following characteristics: (1) The chain carboxylic acid ester compound includes at least one of methyl formate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, or ethyl butyrate; (2) The lithium salt includes at least one of lithium hexafluorophosphate, lithium difluorophosphate, lithium tetrafluoroborate, lithium hexafluoroarsenate, lithium perchlorate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium bis(oxalato)borate, or lithium difluoro(oxalato)borate.

9. An electrical device, which includes the secondary battery according to any one of claims 1 to 8.

Images