Lithium-ion secondary battery, positive electrode sheet, and electric device

Abstract

A lithium-ion secondary battery, a positive electrode sheet, and an electric device. The lithium-ion secondary battery comprises a positive electrode sheet; the positive electrode sheet comprises a lithium oxide positive electrode active material and a potassium salt additive; and a potassium salt decomposes to release potassium ions under a voltage of 3.1 V to 4.2 V. The potassium salt can activate dead lithium in a lithium oxide, increase the capacity per gram of the positive electrode active material, and improve the cycle performance of the lithium oxide.

Description

Lithium-ion secondary batteries, positive electrodes and electrical equipment

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to Chinese patent application No. 2024103027921, filed on March 15, 2024, entitled “Positive Electrode Sheet, Battery and Electrical Equipment,” the entire contents of which are incorporated herein by reference. Technical Field

[0003] The present application relates to the field of lithium battery technology, and in particular to lithium-ion secondary batteries, positive electrode sheets, and electrical equipment. Background Art

[0004] Lithium-ion batteries have made significant progress in recent years, finding widespread application in energy storage systems such as hydropower, thermal, wind, and solar power plants, as well as in electric vehicles, power tools, military equipment, and aerospace. However, in electric vehicles, such as electric bicycles, electric motorcycles, and electric cars, graphite anodes have essentially reached their gram capacity limit as market demands for higher battery life continue to rise, making them incapable of meeting future demands for high-energy-density cells.

[0005] Lithium oxides such as nickel-cobalt-manganese and nickel-cobalt-aluminum are layered oxides used as positive electrode active materials, and their electrochemical performance needs to be further improved.

[0006] Summary of the Invention

[0007] In view of this, the main technical problem solved by this application is to improve the electrochemical properties of layered oxides such as lithium oxide as positive electrode active materials, thereby providing lithium-ion secondary batteries, positive electrode sheets and electrical equipment that can increase the gram capacity of positive electrode active materials and improve capacity attenuation.

[0008] In order to solve the above technical problems, a technical solution adopted in this application is: to provide a lithium-ion secondary battery, the lithium-ion secondary battery includes a positive electrode sheet, a negative electrode sheet and an electrolyte, the positive electrode sheet includes a positive electrode film layer, the positive electrode film layer includes a positive electrode active material and an additive, the positive electrode active material includes lithium oxide, and the additive includes potassium salt, which decomposes into potassium ions at a voltage of 3.1V-4.2V.

[0009] In the technical solution of the embodiment of the present application, a positive electrode plate including lithium oxide is provided, and potassium salt additive is added to the positive electrode film layer so that the potassium salt additive is dispersed in the positive electrode film layer, and the positive electrode plate is assembled into a lithium ion secondary battery, and potassium salt can decompose potassium ions at a voltage of 3.1V-4.2V; lithium oxide is a layered oxide, and during the lithium ion secondary battery cycle, the potassium ions decomposed by the chemical composition can be embedded in or removed from the lithium oxide, so that the dead lithium inside the layered oxide lithium oxide is activated, the gram capacity of the lithium oxide is improved, and the energy density of the positive electrode plate is improved. In addition, due to the potential of the potassium ions decomposed by the potassium salt chemical composition and the lithium ions relative to reversible hydrogen, potassium ions can replace at least part of the lithium ions to participate in the formation of SEI film (solid electrolyte interface film) on the negative electrode plate, the lithium consumption of the lithium oxide in the positive electrode film layer can be reduced, the loss rate of lithium ions is reduced, the capacity stability of the lithium ion secondary battery is improved, and the occurrence of the situation of capacity decay of the lithium ion secondary battery is reduced. In the embodiment of the present application, potassium salt decomposes potassium ions at a voltage of 3.1V-4.2V, and the voltage is low, which reduces the occurrence of side reactions in the formation stage of the lithium ion secondary battery. In addition, the negative electrode sheet in the lithium ion secondary battery may expand or crack during the cycle, and the negative electrode sheet forms a new contact surface (the contact surface in direct contact with the electrolyte) or the SEI film ruptures, etc., which will form or repair the SEI film again. The potassium salt in the embodiment of the present application can participate in the repair of the SEI film during the cycle of the lithium ion secondary battery as an additive, reduce the loss of active lithium, improve the occurrence of the situation of lithium oxide lithium ion secondary battery capacity decay during the cycle, and improve the cycle stability of lithium oxide lithium ion secondary battery. In the embodiment of the present application, the additive is directly arranged in the positive electrode film layer, so that the potassium ions generated after the additive decomposes can participate in the electrode material interface SEI film, and at the same time, widening the electrode surface channel is conducive to lithium ion transmission. In the embodiment of the present application, the cost of potassium salt is lower than that of lithium salt, so that the cost of the positive electrode sheet of the embodiment of the present application is reduced, the gram capacity of lithium oxide is increased, the energy density of lithium oxide is increased, and the cycle performance of lithium ion secondary battery is improved.

[0010] In the embodiment of the present application, the voltage may be the charging voltage of the lithium ion secondary battery in the formation stage, that is, the voltage may be the formation voltage. In other embodiments, the voltage may also be the charging voltage of the lithium ion secondary battery during the cycle process.

[0011] In any embodiment, the potassium salt decomposes potassium ions at a voltage of 3.1 V to 3.9 V. In the embodiment of the present application, the voltage of the potassium salt is within the above range. The lower voltage of the potassium salt can reduce the probability of side reactions during the formation process of the lithium ion secondary battery.

[0012] In any embodiment, potassium salts include tripotassium citrate (C6H5K3O7), potassium sodium citrate (C 12 H 10 K3Na3O 14 ), potassium sulfide (K2S), potassium phosphide (KP3), potassium acetate (CH3COOK), potassium azide (KN3), potassium nitrite (KNO2), potassium citrate (KC6H5O7), potassium oxide (K2O), potassium peroxide (K2O2), potassium oxalate (K2C2O4), potassium squarate (K2C4O4), organic potassium oxide (K2C4O6, K2C6O6), potassium thiosulfate (K2S2O3), potassium sulfite (K2SO3), potassium carbonate (K2CO3), potassium benzoate (KC6H5CO2) or more. In the embodiment of the present application, the voltage for decomposing potassium ions of the above potassium salts is relatively low, and they can be used as additives for the positive electrode film layer.

[0013] In the embodiment of the present application, the lithium oxide may be a nickel-based oxide, and in some embodiments may be lithium nickel cobalt oxide.

[0014] In any embodiment, the lithium nickel cobalt oxide includes lithium nickel cobalt manganese oxide and / or lithium nickel cobalt aluminum oxide. In the embodiment of the present application, the lithium nickel cobalt manganese oxide and the lithium nickel cobalt aluminum oxide are both layered oxides. By adding a potassium salt additive to the positive electrode film layer, the specific capacity, energy density and cycle performance of the lithium nickel cobalt manganese oxide and the lithium nickel cobalt aluminum oxide can be improved.

[0015] In any embodiment, the positive electrode film layer comprises a single layer or multiple layers, wherein at least a portion of the additive and the positive electrode active material are disposed in the same layer. The additive and the positive electrode active material may be in direct contact or in close proximity, and potassium ions released by chemical components in the additive can effectively activate dead lithium in the lithium oxide positive electrode active material.

[0016] In any embodiment, the mass ratio of the potassium salt to the positive electrode active material is (0.5-6):(91-97). In the embodiment of the present application, by controlling the mass ratio of the potassium salt to the positive electrode active material within the above range, the potassium salt in the positive electrode plate can effectively activate the dead lithium of the lithium oxide, increase the gram capacity of the positive electrode active material, increase the energy density of the lithium ion secondary battery, reduce the loss of active lithium, and improve the cycle performance of the lithium ion secondary battery.

[0017] In any embodiment, the mass fraction of potassium salt in the positive electrode film layer is 0.5%-6%. In the embodiment of the present application, by controlling the mass fraction of potassium salt in the positive electrode film layer within the above range, the content of potassium salt in the positive electrode film layer is better in the embodiment of the present application, the more large ion radius (potassium ion) content in the positive electrode film layer, the larger the lithium ion diffusion channel, which is conducive to the release of active lithium ions and the improvement of the capacity of the positive electrode plate; the mass fraction of potassium salt in the positive electrode film layer is within the above range, which can achieve the situation of activating the dead lithium of the positive electrode active material lithium oxide, improve the gram capacity of the positive electrode active material, reduce the loss of active lithium, improve the cycle performance of the lithium ion secondary battery, and make the energy density of the positive electrode plate better and the electrochemical performance of the lithium ion secondary battery better. Potassium salt can be tested by X-ray powder diffractometer (XRD), and the presence of potassium ions can be detected by X-ray photoelectron spectrometer (XPS), and the content of potassium salt can be tested by inductively coupled plasma emission spectrometer (ICP).

[0018] In any embodiment, after the first cycle is completed, the potassium ion content in the positive electrode plate is greater than or equal to 300 PPM. In an embodiment of the present application, after the positive electrode plate is assembled into a lithium-ion secondary battery and undergoes formation and the first cycle, potassium ions remain in the positive electrode plate, and the residual amount of potassium ions can be measured by inductively coupled plasma emission spectrometry (ICP).

[0019] In any embodiment, the volume average particle size DV50 of the potassium salt is 1 μm-30 μm. In the embodiment of the present application, by controlling the volume average particle size of the potassium salt within the above range, on the one hand, the specific surface area of ​​the potassium salt is better, and the potassium salt is easy to decompose under voltage to produce potassium ions; on the other hand, the manufacturability during the production process of the potassium salt slurry is better, the polarization of the potassium salt is smaller, the power density is better, and the cycle performance is better. On the other hand, when the potassium salt slurry is made into a positive electrode film layer, the porosity of the positive electrode film layer is better, the compaction density is higher, and the positive electrode film layer is not easy to break.

[0020] In the embodiments of the present application, the volume average particle size DV50 is common knowledge in the art, has a meaning commonly known in the art, and can be measured by methods and instruments in the art.

[0021] In any embodiment, the volume average particle size DV50 of the potassium salt is 3 μm to 8 μm. By controlling the volume average particle size of the potassium salt within the above range, the specific surface area of ​​the potassium salt is improved, and the potassium salt is easily decomposed under voltage to produce potassium ions. In addition, the manufacturability of the potassium salt slurry is improved, the polarization of the potassium salt is reduced, the power density is improved, and the cycling performance is improved.

[0022] In any embodiment, the volume average particle size DV50 of the positive electrode active material is 4 μm to 6 μm. In the embodiment of the present application, the volume average particle size DV50 of the positive electrode active material is within the above range, so that the positive electrode sheet of the embodiment of the present application has a better specific surface area, better distribution uniformity of the positive electrode active material and the potassium salt additive, and better compaction density of the formed positive electrode sheet.

[0023] In any embodiment, the positive electrode active material comprises a LiNi x Co y M z O2 material, wherein M includes Mn or Al, x+y+z=1, 0.3≤x≤0.95, 0.03≤y≤0.3, 0.02≤z≤0.4. In the embodiment of the present application, the positive electrode active material can be lithium nickel cobalt manganese oxide or lithium nickel cobalt aluminum oxide. In the embodiment of the present application, lithium nickel cobalt manganese oxide and lithium nickel cobalt aluminum oxide can also be doped with other metal elements, such as any one or more of Cr, Co, Cu, Ni, V, Mo, Ti, Zn, Ga, Mg, B and Nb. It can also have a coating layer, such as a metal oxide coating layer. In the embodiment of the present application, after formation or cycling, the battery cell of a LiNi x Co y M z The number of Li atoms in the O2 molecule can be greater than 1, or less than 1 and greater than 0, and the number of O atoms can be greater than 2, or less than 2 and greater than 0.

[0024] In any embodiment, the negative electrode plate includes a negative electrode film layer, the negative electrode film layer includes a negative electrode active material, and the negative electrode active material includes a carbonaceous material, such as graphite, hard carbon, or soft carbon. In the embodiment of the present application, the negative electrode plate includes a carbonaceous material, so that the energy density and cycle stability of the lithium-ion secondary battery in the embodiment of the present application are improved.

[0025] In any embodiment, the negative electrode plate includes metallic lithium or its alloy metal. In the embodiment of the present application, the use of metallic lithium or its alloy metal can significantly improve the volume energy density of the lithium-ion secondary battery in the embodiment of the present application.

[0026] In any embodiment, at the end of formation, the negative electrode plate includes a negative electrode film layer and a solid electrolyte interface film disposed on the negative electrode film layer, wherein the solid electrolyte interface film includes potassium ions. In the embodiment of the present application, the potassium salt additive in the positive electrode film layer can replace at least a portion of the lithium ions or sodium ions in the formation of the SEI film (solid electrolyte interface film) on the negative electrode plate, so that the SEI film contains potassium ions.

[0027] A second aspect of the present application further provides a positive electrode plate, comprising a positive electrode film layer, the positive electrode film layer comprising a positive electrode active material and an additive, the positive electrode active material comprising lithium oxide, the additive comprising a potassium salt, and the potassium salt decomposing into potassium ions at a voltage of 3.1 V to 4.2 V. In an embodiment of the present application, the positive electrode plate comprises the additive, and during the formation process of the positive electrode plate being assembled into a lithium-ion secondary battery, the potassium salt can decompose into potassium ions, so that the positive electrode plate contains the potassium salt additive and potassium ions. The positive electrode plate of the present application has the same advantages as the lithium-ion secondary battery of the first aspect.

[0028] In any embodiment, potassium salts include tripotassium citrate (C6H5K3O7), potassium sodium citrate (C 12 H 10 K3Na3O 14 ), potassium sulfide (K2S), potassium phosphide (KP3), potassium acetate (CH3COOK), potassium azide (KN3), potassium nitrite (KNO2), potassium citrate (KC6H5O7), potassium oxide (K2O), potassium peroxide (K2O2), potassium oxalate (K2C2O4), potassium squarate (K2C4O4), organic potassium oxide (K2C4O6, K2C6O6), potassium thiosulfate (K2S2O3), potassium sulfite (K2SO3), potassium carbonate (K2CO3), potassium benzoate (KC6H5CO2) or more. In the embodiment of the present application, the voltage for decomposing potassium ions of the above potassium salts is relatively low, and they can be used as additives for the positive electrode film layer.

[0029] In the embodiment of the present application, the lithium oxide may be a nickel-based oxide, and in some embodiments may be lithium nickel cobalt oxide.

[0030] In any embodiment, the lithium nickel cobalt oxide includes lithium nickel cobalt manganese oxide and / or lithium nickel cobalt aluminum oxide. In the embodiment of the present application, the lithium nickel cobalt manganese oxide and the lithium nickel cobalt aluminum oxide are both layered oxides. By adding a potassium salt additive to the positive electrode film layer, the specific capacity, energy density and cycle performance of the lithium nickel cobalt manganese oxide and the lithium nickel cobalt aluminum oxide can be improved.

[0031] In any embodiment, the positive electrode film layer comprises a single layer or multiple layers, wherein at least a portion of the additive and the positive electrode active material are disposed in the same layer. The additive and the positive electrode active material may be in direct contact or in close proximity, and potassium ions released by chemical components in the additive can effectively activate dead lithium in the lithium oxide positive electrode active material.

[0032] In any embodiment, the mass ratio of the potassium salt to the positive electrode active material is (0.5-6):(91-97). In the embodiment of the present application, by controlling the mass ratio of the potassium salt to the positive electrode active material within the above range, the potassium salt in the positive electrode plate can effectively activate the dead lithium of the lithium oxide, increase the gram capacity of the positive electrode active material, increase the energy density of the lithium ion secondary battery, reduce the loss of active lithium, and improve the cycle performance of the lithium ion secondary battery.

[0033] In any embodiment, the volume average particle size DV50 of the potassium salt is 1 μm-30 μm. In the embodiment of the present application, by controlling the volume average particle size of the potassium salt within the above range, on the one hand, the specific surface area of ​​the potassium salt is better, and the potassium salt is easy to decompose under voltage to produce potassium ions; on the other hand, the manufacturability during the production process of the potassium salt slurry is better, the polarization of the potassium salt is smaller, the power density is better, and the cycle performance is better. On the other hand, when the potassium salt slurry is made into a positive electrode film layer, the porosity of the positive electrode film layer is better, the compaction density is higher, and the positive electrode film layer is not easy to break.

[0034] A third aspect of the present application further provides an electrical device comprising the lithium-ion secondary battery of the first aspect or the positive electrode sheet of the second aspect. In an embodiment of the present application, the lithium-ion secondary battery of the first aspect or the positive electrode sheet of the second aspect has at least the same advantages as the lithium-ion secondary battery of the first aspect or the positive electrode sheet of the second aspect. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] FIG1 is a schematic structural diagram of a vehicle provided in one embodiment of the present application;

[0036] FIG2 is a schematic diagram of the exploded structure of a lithium-ion secondary battery provided in one embodiment of the present application;

[0037] FIG3 is a schematic diagram of the exploded structure of a battery cell provided in one embodiment of the present application. DETAILED DESCRIPTION

[0038] Below, the battery cell, lithium-ion secondary battery and electrical equipment of the present application are described in detail with appropriate reference to the accompanying drawings. However, there may be cases where unnecessary detailed descriptions are omitted. For example, there may be cases where detailed descriptions of well-known matters and repeated descriptions of actually the same structure are omitted. This is to avoid the following description from becoming unnecessarily lengthy and to facilitate the understanding of those skilled in the art. In addition, the drawings and the following description are provided for those skilled in the art to fully understand the present application and are not intended to limit the subject matter described in the claims.

[0039] " range " disclosed in the present application is limited in the form of lower limit and upper limit, and given range is limited by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundary of special range. The scope limited in this way can be to include end value or not include end value, and can be arbitrarily combined, that is, any lower limit can form a range with any upper limit combination. For example, if the scope of 60-120 and 80-110 is listed for specific parameters, it is understood that the scope of 60-110 and 80-120 is also expected. In addition, if the minimum range value 1 and 2 are listed, and if the maximum range value 3,4 and 5 are listed, then the following range can all be expected: 1-3, 1-4, 1-5, 2-3, 2-4 and 2-5. In this application, unless otherwise specified, the numerical range " ab " represents the abbreviation of any real number combination between a and b, wherein a and b are all real numbers. For example, a numerical range of "0-5" indicates that all real numbers between "0-5" are listed herein, and "0-5" is simply an abbreviation for these numerical combinations. Furthermore, when a parameter is expressed as an integer ≥ 2, this 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.

[0040] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0041] 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.

[0042] Unless otherwise specified, all steps of the present application may be performed sequentially or randomly, preferably sequentially. For example, a method includes steps (a) and (b), which indicates that the method may include steps (a) and (b) performed sequentially, or may include steps (b) and (a) performed sequentially. For example, a method may further include step (c), which indicates 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.

[0043] Unless otherwise specified, the terms "include" and "comprising" used in this application may be open-ended or closed-ended. For example, "include" and "comprising" may indicate that other components not listed may also be included or that only the listed components are included.

[0044] Unless otherwise specified, the term "or" is used in this application to be inclusive. For example, the phrase "A or B" means "A, B, or both A and B." More specifically, the condition "A or B" is satisfied if any of the following conditions are met: A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).

[0045] There is dead lithium inside the layered lithium oxide, which cannot be embedded in or removed from the positive electrode active material, resulting in a low specific capacity of the positive electrode active material. In addition, when layered lithium oxide is assembled into a lithium-ion secondary battery as a positive electrode active material, active lithium is continuously consumed during the formation and early cycle process, resulting in the formation of a relatively stable SEI film at the negative electrode, which causes the capacity of the lithium-ion secondary battery to decay rapidly in the early cycle. During the middle and late stages of use of lithium-ion secondary batteries, the negative electrode sheets are prone to expansion and increase in volume. During this process, active lithium is consumed, further forming an SEI film to achieve the effect of repairing the SEI film of the negative electrode sheet, causing the lithium-ion secondary battery to easily decay in the middle and late stages of the cycle.

[0046] To this end, the present application provides a positive electrode plate, as shown in Figure 1, and provides a lithium-ion secondary battery. The lithium-ion secondary battery includes a positive electrode plate, the positive electrode plate includes a positive electrode film layer, the positive electrode film layer includes a positive electrode active material and an additive, the positive electrode active material includes lithium oxide, and the additive includes potassium salt, which decomposes potassium ions at a voltage of 3.1V-4.2V.

[0047] In the technical solution of the embodiment of the present application, the positive electrode plate of the lithium-ion secondary battery contains lithium oxide. By adding a potassium salt additive to the positive electrode film layer of the positive electrode plate, the potassium salt additive in the lithium-ion secondary battery can decompose into potassium ions at a voltage of 3.1V-4.2V; taking lithium nickel cobalt oxide as an example, lithium nickel cobalt oxide is a layered oxide. During the cycle of the lithium-ion secondary battery, the potassium ions decomposed can be embedded in or released from the lithium nickel cobalt oxide, so that the dead lithium inside the layered oxide lithium nickel cobalt oxide is activated, thereby improving the gram capacity of the lithium nickel cobalt oxide and improving the energy density of the positive electrode plate.

[0048] In addition, since the potassium ions released by the potassium salt component are similar to the potential of lithium ions relative to reversible hydrogen, potassium ions can replace at least part of the lithium ions to participate in the formation of the SEI film (solid electrolyte membrane) on the negative electrode plate, which can reduce the lithium consumption of the lithium nickel cobalt oxide in the positive electrode film layer, reduce the loss rate of lithium ions, improve the capacity stability of the lithium ion secondary battery, and reduce the occurrence of the capacity decay of the lithium ion secondary battery. In the embodiment of the present application, the potassium salt decomposes potassium ions at a voltage of 3.1V-4.2V, and the required voltage is low, which is beneficial to the formation of the lithium ion secondary battery of the positive electrode plate and reduces the occurrence of side reactions of the lithium ion secondary battery.

[0049] In addition, the negative electrode in the lithium-ion secondary battery may expand or crack during the cycle, and the negative electrode may form a new contact surface (the contact surface in direct contact with the electrolyte) or the SEI film may rupture, which will cause the SEI film to be formed or repaired again. The potassium salt in the embodiment of the present application can be used as an additive to participate in the formation of the SEI film during the cycle of the lithium-ion secondary battery, reduce the loss of active lithium, improve the capacity attenuation of the lithium nickel cobalt oxide lithium ion secondary battery during the cycle, and improve the cycle stability of the lithium nickel cobalt oxide lithium ion secondary battery.

[0050] In the embodiment of the present application, the additive is directly provided in the positive electrode film layer, so that the potassium ions in the additive can better activate the dead lithium in the lithium oxide positive electrode active material. This is different from the effect achieved by introducing potassium doping into the positive electrode active material and adding potassium salt into the electrolyte in the related art; a potassium salt that can be decomposed at a specific voltage is introduced into the positive electrode film layer, and the potassium ions obtained by decomposition are embedded in or removed from the positive electrode active material, which is beneficial to the removal of lithium ions (increase of more than 0.6%) and the embedding of lithium ions (increase of more than 0.6%) of the positive electrode active material. It is speculated that the addition of potassium salt to the positive electrode film layer can widen the ion channel, activate dead lithium, and slow down the consumption of lithium; at the same time, the amount of potassium ions introduced into the additive in the embodiment of the present application is significantly greater than the amount of potassium ions doped into the positive electrode active material and the additive in the electrolyte, which can be detected by ICP on the positive and negative electrode plates.

[0051] In the embodiments of the present application, the cost of potassium salts is lower than that of lithium salts, thereby reducing the cost of the positive electrode sheets of the embodiments of the present application, increasing the specific capacity of the lithium oxide, increasing the energy density of the lithium oxide, and improving the cycling performance of the lithium-ion secondary battery. The voltage can be 3.1V, 3.4V, 3.5V, 3.9V, 4.0V, 4.2V, or a range of any two of the above values, such as 3.1V-3.4V, 3.4V-3.9V, or 3.9V-4.2V.

[0052] In any embodiment, the potassium salt decomposes to release potassium ions at a voltage of 3.1V-3.9V. In the embodiments of the present application, the voltage of the potassium salt is within the above range, so that the voltage of the potassium salt is low, which can reduce the occurrence of side reactions. The voltage can be 3.1V, 3.4V, 3.5V, 3.6V, 3.9V, etc., or a range consisting of any two of the above values, such as 3.1V-3.4V, 3.4V-3.6V, 3.6V-3.9V, etc.

[0053] In any embodiment, potassium salts include tripotassium citrate (C6H5K3O7), potassium sodium citrate (C 12 H 10 K3Na3O 14 ), potassium sulfide (K2S), potassium phosphide (KP3), potassium acetate (CH3COOK), potassium azide (KN3), potassium nitrite (KNO2), potassium citrate (KC6H5O7), potassium oxide (K2O), potassium peroxide (K2O2), potassium oxalate (K2C2O4), potassium squarate (K2C4O4), organic potassium oxide (K2C4O6, K2C6O6), potassium thiosulfate (K2S2O3), potassium sulfite (K2SO3), potassium carbonate (K2CO3), potassium benzoate (KC6H5CO2) or more. In the embodiment of the present application, the voltage for decomposing potassium ions of the above potassium salts is relatively low, and they can be used as additives for the positive electrode film layer.

[0054] In any embodiment, the lithium oxide includes lithium nickel cobalt manganese oxide and / or lithium nickel cobalt aluminum oxide. In the embodiment of the present application, lithium nickel cobalt manganese oxide and lithium nickel cobalt aluminum oxide are both layered oxides. By adding potassium salt additives to the positive electrode film layer, the specific capacity, energy density and cycle performance of lithium nickel cobalt manganese oxide and lithium nickel cobalt aluminum oxide can be improved.

[0055] In any embodiment, the positive electrode film layer includes a single layer or multiple layers, wherein: at least part of the additives and the positive electrode active material are arranged in the same layer. The additives and the positive electrode active material can be in direct contact, or the distance between the additives and the positive electrode active material is relatively close, and the potassium ions released from the chemical components in the additives can better activate the dead lithium in the lithium oxide positive electrode active material. In the embodiment of the present application, the positive electrode film layer is a single layer, and the additives and the positive electrode active material are mixed in the same layer. In other embodiments, the positive electrode film layer can also be two or more layers, and the two or more positive electrode film layers are sequentially stacked on one side or both sides of the current collector. The materials of the positive electrode active materials of the two adjacent positive electrode film layers can be the same or different. The additives can be arranged in one positive electrode film layer, or in two or more positive electrode film layers.

[0056] In some embodiments, the mass ratio of potassium salt to positive electrode active material is (0.5-6): (91-97). In the embodiment of the present application, by controlling the mass ratio of potassium salt to positive electrode active material in the above range, the potassium salt in the positive electrode plate can effectively activate the dead lithium of lithium oxide, increase the gram capacity of the positive electrode active material, increase the energy density of the lithium ion secondary battery, reduce the loss of active lithium, and improve the cycle performance of the lithium ion secondary battery. Among them, the mass ratio of potassium salt to positive electrode active material can be 0.5:91, 0.8:91, 0.8:92, 1:93, 1.5:93, 2:93, 2.5:93, 3:93, 3.5:93, 4:93, 5:93, 6:93, 0.5:94, 0.8:95, 1:96, 1.5:97, 3.5:97, 5:97, 6:97, etc. Or it can be a range value consisting of any two of the above values, for example, (0.5-2):(91-93), (2-4):(93-95), (4-6):(95-97), etc.

[0057] In some embodiments, the mass fraction of potassium salt in the positive electrode film layer is 0.5%-6%. In the embodiment of the present application, by controlling the mass fraction of potassium salt in the positive electrode film layer within the above range, the content of potassium salt in the positive electrode film layer is better in the embodiment of the present application, the more large ion radius (potassium ion) content in the positive electrode film layer, the larger the lithium ion diffusion channel, which is conducive to the escape of active lithium ions and the improvement of the capacity of the positive electrode plate; the mass fraction of potassium salt in the positive electrode film layer is within the above range, which can achieve the activation of dead lithium of lithium oxide, the positive electrode active material, the increase of the gram capacity of the positive electrode active material, the reduction of the loss of active lithium, the improvement of the cycle performance of the lithium ion secondary battery, and the better energy density of the positive electrode plate and the better electrochemical performance of the lithium ion secondary battery. In some embodiments, the positive electrode film layer may further include a conductive agent and a binder. By controlling the mass fraction of potassium salt in the positive electrode film layer within the above range, it is beneficial to control the energy density of the positive electrode plate to be better. In some embodiments of the present application, the mass fraction of the potassium salt in the positive electrode film layer may be 0.5%, 1%, 1.2%, 1.5%, 1.8%, 2%, 2.4%, 2.8%, 3%, 3.3%, 3.5%, 4%, 5%, 6%, etc., or a range of any two of the above values, for example, 0.5%-1.2%, 1.2%-2.4%, 2.4%-3.5%, 0.5%-3.5%, 3.5%-6%, etc.

[0058] In any embodiment, upon completion of the first cycle, the potassium ion content in the positive electrode plate is greater than or equal to 300 PPM. In an embodiment of the present application, after the positive electrode plate is assembled into a lithium-ion secondary battery and undergoes formation and the first cycle, potassium ions still remain in the positive electrode plate, and the residual amount of potassium ions can be measured by inductively coupled plasma emission spectrometry (ICP).

[0059] In some embodiments, the volume average particle size DV50 of the potassium salt is 1 μm-30 μm. In the embodiment of the present application, by controlling the volume average particle size of the potassium salt within the above range, on the one hand, the specific surface area of ​​the potassium salt is better, and the potassium salt is easy to decompose under voltage to produce potassium ions; on the other hand, the manufacturability during the production process of the potassium salt slurry is better, the polarization of the potassium salt is smaller, the power density is better, and the cycle performance is better. On the other hand, when the potassium salt slurry is made into a positive electrode film layer, the porosity of the positive electrode film layer is better, the compaction density is larger, and the positive electrode film layer is not easy to break. In some embodiments of the present application, the volume average particle size DV50 of the potassium salt can be 1 μm, 3 μm, 5 μm, 8 μm, 10 μm, 15 μm, 20 μm, 30 μm, etc., or a range value composed of any two of the above values, for example, 1 μm-8 μm, 8 μm-15 μm, 15 μm-30 μm, etc.

[0060] In some embodiments, the volume average particle size DV50 of the potassium salt is 3μm-8μm. By controlling the volume average particle size of the potassium salt within the above range, the specific surface area of ​​the potassium salt is improved, and the potassium salt is easily decomposed under voltage to produce potassium ions; on the other hand, the manufacturability of the potassium salt in the slurry production process is improved, the polarization of the potassium salt is small, the power density is better, and the cycle performance is better. In some embodiments of the present application, the volume average particle size DV50 of the potassium salt can be 3μm, 5μm, 6μm, 8μm, etc., or a range of any two of the above values, for example, 3μm-5μm, 5μm-6μm, 6μm-8μm, etc.

[0061] In any embodiment, the volume average particle size DV50 of the positive electrode active material is 4μm-6μm. In the embodiment of the present application, the volume average particle size DV50 of the positive electrode active material is in the above range, so that the specific surface area of ​​the positive electrode plate of the embodiment of the present application is better, the distribution uniformity of the positive electrode active material and the potassium salt additive is better, and the compaction density of the positive electrode plate is better. The volume average particle size DV50 of the positive electrode active material can be 4μm, 4.5μm, 5μm, 5.5μm, 6μm, etc., or a range of any two of the above values, for example, 4μm-5μm, 5μm-5.5μm, 5.5μm-6μm, etc.

[0062] In some embodiments, in any embodiment, the positive electrode active material comprises a LiNi x Co y M zO2 material, wherein M includes Mn or Al, x+y+z=1, 0.3≤x≤0.95, 0.03≤y≤0.3, 0.02≤z≤0.4. In the embodiment of the present application, the positive electrode active material can be lithium nickel cobalt manganese oxide or lithium nickel cobalt aluminum oxide. In the embodiment of the present application, lithium nickel cobalt manganese oxide and lithium nickel cobalt aluminum oxide can also be doped with other metal elements, such as any one or more of Cr, Co, Cu, Ni, V, Mo, Ti, Zn, Ga, Mg, B and Nb. It can also have a coating layer, such as a metal oxide coating layer. In the later stage of the lithium ion secondary battery in the embodiment of the present application, after formation or cycling, LiNi x Co y M z Among the atomic number of constituent elements of the O2 material, the number of Li element atoms may be greater than 1, or less than 1 and greater than 0, and the number of O element atoms may be greater than 2, or less than 2 and greater than 0.

[0063] In some embodiments, the negative electrode plate includes a negative electrode film layer, the negative electrode film layer includes a negative electrode active material, and the negative electrode active material includes graphite. In the embodiment of the present application, the negative electrode plate includes a graphite negative electrode active material, so that the lithium ion secondary battery in the embodiment of the present application has better cycle stability.

[0064] In some embodiments, the negative electrode plate includes metallic lithium or its alloy metal. In the embodiments of the present application, the use of metallic lithium or its alloy metal can significantly improve the volume energy density of the lithium-ion secondary battery in the embodiments of the present application.

[0065] In some embodiments, at the end of formation, the negative electrode plate includes a negative electrode film layer and a solid electrolyte interface film disposed on the negative electrode film layer, wherein the solid electrolyte interface film includes potassium ions. In embodiments of the present application, the potassium salt additive in the positive electrode film layer can replace at least a portion of the lithium ions or sodium ions in the formation of the SEI film (solid electrolyte interface film) on the negative electrode plate, so that the SEI film contains potassium ions.

[0066] The second aspect of the present application further provides a positive electrode plate, as shown in FIG1 , providing a positive electrode plate, the positive electrode plate comprising a positive electrode film layer, the positive electrode film layer comprising a positive electrode active material and an additive, the positive electrode active material comprising lithium oxide, the additive comprising a potassium salt, and the potassium salt decomposing to produce potassium ions at a voltage of 3.1V-4.2V. The positive electrode plate in an embodiment of the present application includes an additive, and the potassium salt additive can decompose to produce potassium ions at a voltage of 3.1V-4.2V when the positive electrode plate is assembled into a lithium-ion secondary battery, so that the positive electrode plate contains the potassium salt additive and potassium ions, so that the positive electrode plate of the second aspect of the present application has the same advantages as the lithium-ion secondary battery of the first aspect.

[0067] In the embodiments of the present application, the cost of potassium salts is lower than that of lithium salts, thereby reducing the cost of the positive electrode sheets of the embodiments of the present application, increasing the specific capacity of the lithium oxide, increasing the energy density of the lithium oxide, and improving the cycling performance of the lithium-ion secondary battery. The voltage can be 3.1V, 3.4V, 3.5V, 3.9V, 4.0V, 4.2V, or a range of any two of the above values, such as 3.1V-3.4V, 3.4V-3.9V, or 3.9V-4.2V.

[0068] In any embodiment, the potassium salt decomposes to release potassium ions at a voltage of 3.1V-3.9V. In the embodiments of the present application, the voltage of the potassium salt is within the above range, so that the voltage of the potassium salt is low, which can reduce the occurrence of side reactions. The voltage can be 3.1V, 3.4V, 3.5V, 3.6V, 3.9V, etc., or a range consisting of any two of the above values, such as 3.1V-3.4V, 3.4V-3.6V, 3.6V-3.9V, etc.

[0069] In any embodiment, potassium salts include tripotassium citrate (C6H5K3O7), potassium sodium citrate (C 12 H 10 K3Na3O 14 ), potassium sulfide (K2S), potassium phosphide (KP3), potassium acetate (CH3COOK), potassium azide (KN3), potassium nitrite (KNO2), potassium citrate (KC6H5O7), potassium oxide (K2O), potassium peroxide (K2O2), potassium oxalate (K2C2O4), potassium squarate (K2C4O4), organic potassium oxide (K2C4O6, K2C6O6), potassium thiosulfate (K2S2O3), potassium sulfite (K2SO3), potassium carbonate (K2CO3), potassium benzoate (KC6H5CO2) or more. In the embodiment of the present application, the voltage for decomposing potassium ions of the above potassium salts is relatively low, and they can be used as additives for the positive electrode film layer.

[0070] In any embodiment, the lithium oxide includes lithium nickel cobalt manganese oxide and / or lithium nickel cobalt aluminum oxide. In the embodiment of the present application, lithium nickel cobalt manganese oxide and lithium nickel cobalt aluminum oxide are both layered oxides. By adding potassium salt additives to the positive electrode film layer, the specific capacity, energy density and cycle performance of lithium nickel cobalt manganese oxide and lithium nickel cobalt aluminum oxide can be improved.

[0071] In any embodiment, the positive electrode film layer includes a single layer or multiple layers, wherein: at least part of the additives and the positive electrode active material are arranged in the same layer. The additives and the positive electrode active material can be in direct contact, or the distance between the additives and the positive electrode active material is relatively close, and the potassium ions released from the chemical components in the additives can better activate the dead lithium in the lithium oxide positive electrode active material. In the embodiment of the present application, the positive electrode film layer is a single layer, and the additives and the positive electrode active material are mixed in the same layer. In other embodiments, the positive electrode film layer can also be two or more layers, and the two or more positive electrode film layers are sequentially stacked on one side or both sides of the current collector. The materials of the positive electrode active materials of the two adjacent positive electrode film layers can be the same or different. The additives can be arranged in one positive electrode film layer, or in two or more positive electrode film layers.

[0072] In some embodiments, the mass ratio of potassium salt to positive electrode active material is (0.5-6): (91-97). In the embodiment of the present application, by controlling the mass ratio of potassium salt to positive electrode active material in the above range, the potassium salt in the positive electrode plate can effectively activate the dead lithium of lithium oxide, increase the gram capacity of the positive electrode active material, increase the energy density of the lithium ion secondary battery, reduce the loss of active lithium, and improve the cycle performance of the lithium ion secondary battery. Among them, the mass ratio of potassium salt to positive electrode active material can be 0.5:91, 0.8:91, 0.8:92, 1:93, 1.5:93, 2:93, 2.5:93, 3:93, 3.5:93, 4:93, 5:93, 6:93, 0.5:94, 0.8:95, 1:96, 1.5:97, 3.5:97, 5:97, 6:97, etc. Or it can be a range value consisting of any two of the above values, for example, (0.5-2):(91-93), (2-4):(93-95), (4-6):(95-97), etc.

[0073] In some embodiments, the volume average particle size DV50 of the potassium salt is 1 μm-30 μm. In the embodiment of the present application, by controlling the volume average particle size of the potassium salt within the above range, on the one hand, the specific surface area of ​​the potassium salt is better, and the potassium salt is easy to decompose under voltage to produce potassium ions; on the other hand, the manufacturability during the production process of the potassium salt slurry is better, the polarization of the potassium salt is smaller, the power density is better, and the cycle performance is better. On the other hand, when the potassium salt slurry is made into a positive electrode film layer, the porosity of the positive electrode film layer is better, the compaction density is larger, and the positive electrode film layer is not easy to break. In some embodiments of the present application, the volume average particle size DV50 of the potassium salt can be 1 μm, 3 μm, 5 μm, 8 μm, 10 μm, 15 μm, 20 μm, 30 μm, etc., or a range value composed of any two of the above values, for example, 1 μm-8 μm, 8 μm-15 μm, 15 μm-30 μm, etc.

[0074] A third aspect of the present application further provides an electrical device comprising the lithium-ion secondary battery of the first aspect or the positive electrode sheet of the second aspect. The embodiments of the present application comprising the lithium-ion secondary battery of the first aspect or the positive electrode sheet of the second aspect have at least the same advantages as the lithium-ion secondary battery of the first aspect or the positive electrode sheet of the second aspect.

[0075] The lithium-ion secondary battery disclosed in the embodiments of the present application can be used in various energy storage systems that use lithium-ion secondary batteries as power sources or use lithium-ion secondary batteries as energy storage elements. The electrical equipment can be, but is not limited to, mobile phones, tablets, laptops, electric toys, power tools, battery cars, electric cars, ships, spacecraft, etc. Among them, electric toys can include fixed or mobile electric toys, such as game consoles, electric car toys, electric ship toys, and electric airplane toys, etc., and spacecraft can include airplanes, rockets, space shuttles, and spacecraft, etc.

[0076] For the convenience of description, the following embodiments are described with reference to FIG. 1 , in which an electrical device in an embodiment of the present application is a vehicle 1000 as an example.

[0077] Figure 1 is a structural schematic diagram of a vehicle 1000 provided in some embodiments of the present application. The vehicle 1000 can be a fuel vehicle, a gas vehicle or a new energy vehicle. The new energy vehicle can be a pure electric vehicle, a hybrid vehicle or an extended-range vehicle, etc. A lithium-ion secondary battery 100 is provided inside the vehicle 1000. The lithium-ion secondary battery 100 can be provided at the bottom, head or tail of the vehicle 1000. The lithium-ion secondary battery 100 can be used to power the vehicle 1000. For example, the lithium-ion secondary battery 100 can serve as an operating power source for the vehicle 1000. The vehicle 1000 may also include a controller 200 and a motor 300. The controller 200 is used to control the lithium-ion secondary battery 100 to power the motor 300, for example, for starting, navigating and operating power requirements of the vehicle 1000 during driving.

[0078] In some embodiments of the present application, the lithium-ion secondary battery 100 can serve not only as an operating power source for the vehicle 1000 , but also as a driving power source for the vehicle 1000 , replacing or partially replacing fuel or natural gas to provide driving power for the vehicle 1000 .

[0079] Please refer to Figure 2, which is a schematic diagram of the exploded structure of a lithium-ion secondary battery 100 provided in some embodiments of the present application. The lithium-ion secondary battery 100 includes a housing 10 and a battery cell 20, and the battery cell 20 is accommodated in the housing 10. The housing 10 is used to provide a storage space for the battery cell 20, and the housing 10 can adopt a variety of structures. In some embodiments, the housing 10 may include a first part 11 and a second part 12, and the first part 11 and the second part 12 cover each other, and the first part 11 and the second part 12 jointly define a storage space for accommodating the battery cell 20. The second part 12 can be a hollow structure with one end open, and the first part 11 can be a plate-like structure, and the first part 11 covers the open side of the second part 12, so that the first part 11 and the second part 12 jointly define a storage space; the first part 11 and the second part 12 can also be hollow structures with one side open, and the open side of the first part 11 covers the open side of the second part 12. Of course, the box body 10 formed by the first part 11 and the second part 12 can be in various shapes, such as a cylinder, a cuboid, etc.

[0080] In the lithium-ion secondary battery 100, there may be multiple battery cells 20, and the multiple battery cells 20 may be connected in series, in parallel, or in a hybrid connection. A hybrid connection refers to a combination of series and parallel connections among the multiple battery cells 20. The multiple battery cells 20 may be directly connected in series, in parallel, or in a hybrid connection, and then the entire structure formed by the multiple battery cells 20 is housed within the housing 10. Of course, the lithium-ion secondary battery 100 may also be in the form of a lithium-ion secondary battery module, in which multiple battery cells 20 are first connected in series, in parallel, or in a hybrid connection, and then the multiple lithium-ion secondary battery modules are further connected in series, in parallel, or in a hybrid connection to form an entire structure, which is then housed within the housing 10. The lithium-ion secondary battery 100 may also include other structures, for example, the lithium-ion secondary battery 100 may further include a busbar component for electrically connecting the multiple battery cells 20.

[0081] Each battery cell 20 may be a secondary lithium-ion secondary battery or a primary lithium-ion secondary battery; it may also be a lithium-sulfur lithium-ion secondary battery, a sodium-ion lithium-ion secondary battery, or a magnesium-ion lithium-ion secondary battery, but is not limited thereto. The battery cell 20 may be cylindrical, flat, rectangular, or in other shapes.

[0082] Please refer to Figure 3, which is a schematic diagram of the exploded structure of a battery cell 20 provided in some embodiments of the present application. A battery cell 20 is the smallest unit that makes up a lithium-ion secondary battery. As shown in Figure 3, a battery cell 20 includes an end cap 21, a housing 22, a cell assembly 23, and other functional components.

[0083] The end cap 21 is a component that covers the opening of the housing 22 to isolate the internal environment of the battery cell 20 from the external environment. The shape of the end cap 21 can be adapted to the shape of the housing 22 to match the housing 22. Optionally, the end cap 21 can be made of a material with a certain hardness and strength (such as an aluminum alloy). This prevents the end cap 21 from deforming when subjected to compression or collision, giving the battery cell 20 greater structural strength and improved safety. The end cap 21 can be provided with functional components such as electrode terminals 21a. The electrode terminals 21a can be used to electrically connect to the battery cell assembly 23 to output or input electrical energy to the battery cell 20. In some embodiments, the end cap 21 can also be provided with a pressure relief mechanism for relieving internal pressure when the internal pressure or temperature of the battery cell 20 reaches a threshold. The end cap 21 can also be made of a variety of materials, such as copper, iron, aluminum, stainless steel, aluminum alloy, plastic, etc., and the embodiments of the present application are not particularly limited in this regard. In some embodiments, an insulating member may be provided inside the end cap 21 to isolate the electrical connection components in the housing 22 from the end cap 21 to reduce the risk of short circuit. For example, the insulating member may be made of plastic, rubber, or the like.

[0084] The housing 22 is a component that cooperates with the end cap 21 to form the internal environment of the battery cell 20. This internal environment can be used to accommodate the battery cell assembly 23, electrolyte, and other components. The housing 22 and end cap 21 can be separate components. An opening can be provided in the housing 22, and the end cap 21 is placed over the opening to form the internal environment of the battery cell 20. Alternatively, the end cap 21 and housing 22 can be integrated. Specifically, the end cap 21 and housing 22 can form a common connection surface before other components are inserted into the housing. When the interior of the housing 22 needs to be enclosed, the end cap 21 is placed over the housing 22. The housing 22 can have a variety of shapes and sizes, such as a rectangular parallelepiped, a cylindrical shape, a hexagonal prism, etc. Specifically, the shape of the housing 22 can be determined based on the specific shape and size of the battery cell assembly 23. The housing 22 can be made of a variety of materials, such as copper, iron, aluminum, stainless steel, aluminum alloy, plastic, etc., and this embodiment of the present application does not impose any specific limitations on this.

[0085] The cell assembly 23 is a component in the battery cell 20 where electrochemical reactions occur. One or more cell assemblies 23 may be contained in the shell 22. The cell assembly 23 is mainly formed by winding or stacking positive and negative electrode sheets, and a separator is usually provided between the positive and negative electrode sheets. The parts of the positive and negative electrode sheets with active materials constitute the main body of the cell assembly, and the parts of the positive and negative electrode sheets without active materials each constitute a tab 23a. The positive and negative electrode tabs may be located together at one end of the main body or respectively at both ends of the main body. During the charge and discharge process of the lithium-ion secondary battery 100, the positive active material and the negative active material react with the electrolyte, and the tabs 23a connect the electrode terminals to form a current loop.

[0086] [Positive electrode]

[0087] In some embodiments, the positive electrode sheet includes the positive electrode sheet of the second aspect of the present application, and the positive electrode film layer is provided on at least one surface of a current collector. For the sake of distinction, the current collector is referred to as a positive electrode current collector.

[0088] As an example, the positive electrode current collector has two surfaces opposite to each other in its thickness direction, and the positive electrode film layer is disposed on either or both of the two opposite surfaces of the positive electrode current collector.

[0089] 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.).

[0090] In some embodiments, the positive electrode film layer includes a binder. The binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), a vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, a vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, a tetrafluoroethylene-hexafluoropropylene copolymer, and a fluorine-containing acrylate resin.

[0091] In some embodiments, the positive electrode film layer includes a conductive agent. As an example, the conductive agent may include at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0092] In some embodiments, the positive electrode sheet can be prepared by the following method: the components used to prepare the positive electrode sheet, such as the positive electrode active material, the conductive agent, the binder, the potassium salt additive 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 current collector, and after drying, cold pressing and other processes, the positive electrode sheet can be obtained.

[0093] In another embodiment, the positive electrode sheet can also be prepared in the following manner: 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 current collector, and dried to form a positive electrode active material layer; the potassium salt additive, the conductive agent and the binder are dispersed in a solvent (such as N-methylpyrrolidone) to form an additive slurry, and the additive slurry is coated on the positive electrode active material layer. After drying, cold pressing and other processes, the positive electrode sheet can be obtained.

[0094] [Negative electrode]

[0095] The negative electrode sheet includes a negative electrode current collector and a negative electrode film layer provided on at least one surface of the negative electrode current collector, wherein the negative electrode film layer includes a negative electrode active material.

[0096] As an example, the negative electrode current collector has two surfaces opposite to each other in its thickness direction, and the negative electrode film layer is disposed on either or both of the two opposite surfaces of the negative electrode current collector.

[0097] 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.).

[0098] In some embodiments, the negative electrode active material may be a negative electrode active material for lithium ion secondary batteries that is well known in the art. As an example, the negative electrode active material may include at least one of the following materials: artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, lithium titanate, etc. The silicon-based material may be selected from at least one of elemental silicon, silicon oxides, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. The tin-based material may be selected from at least one of elemental tin, tin oxides, and tin alloys. However, the present application is not limited to these materials, and other traditional materials that can be used as negative electrode active materials for lithium ion secondary batteries may also be used. These negative electrode active materials may be used alone or in combination of two or more.

[0099] In some embodiments, the negative electrode film 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).

[0100] In some embodiments, the negative electrode film 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.

[0101] In some embodiments, the negative electrode film layer may optionally include other additives, such as a thickener (eg, sodium carboxymethyl cellulose (CMC-Na)).

[0102] 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.

[0103] [Electrolytes]

[0104] The electrolyte conducts ions between the positive and negative electrodes. This application does not specify the type of electrolyte, and the electrolyte can be selected based on the needs. For example, the electrolyte can be liquid, gel, or solid.

[0105] In some embodiments, the electrolyte is an electrolyte solution comprising an electrolyte salt and a solvent.

[0106] In some embodiments, the electrolyte salt may be selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalatoborate, lithium dioxalatoborate, lithium difluorodioxalatophosphate, and lithium tetrafluorooxalatophosphate.

[0107] 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.

[0108] In some embodiments, the electrolyte may further include additives. For example, the additives may include negative electrode film-forming additives, positive electrode film-forming additives, and additives capable of improving certain properties of the lithium-ion secondary battery, such as additives that improve the overcharge performance of the lithium-ion secondary battery, and additives that improve the high or low temperature performance of the lithium-ion secondary battery.

[0109] [Isolation film]

[0110] In some embodiments, the lithium-ion secondary battery further includes a separator. The present application has no particular limitation on the type of separator, and any known porous separator with good chemical and mechanical stability can be selected.

[0111] In some embodiments, the material of the separator can be selected from at least one of glass fiber, non-woven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator can 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 can be the same or different, without particular limitation.

[0112] In some embodiments, the positive electrode sheet, the negative electrode sheet, and the separator can be made into a battery cell assembly through a winding process or a lamination process, and a lithium-ion secondary battery can be formed by liquid injection or the like.

[0113] The present application has no particular limitation on the shape of the lithium-ion secondary battery, which may be cylindrical, square, or any other shape.

[0114] The beneficial effects of the present application are further illustrated below with reference to the examples.

[0115] In order to make the technical problems, technical solutions and beneficial effects solved by the embodiments of the present application clearer, the following will be further described in detail with reference to the embodiments and drawings. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. The following description of at least one exemplary embodiment is actually only illustrative and is in no way intended to limit the present application and its applications. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0116] Example 1

[0117]

Preparation of positive electrode sheet

[0118] The positive electrode active material lithium nickel cobalt manganese oxide (LiNi 0.65 Co 0.15 Mn 0.2 O2, Ni65), potassium salt additive C6H5K3O7, conductive carbon and polyvinylidene fluoride (PVDF) are mixed in a mass ratio of 94:3:1.5:1.5, and then solvent N-methylpyrrolidone (NMP) is added to adjust the solid content to 70%-80%. After stirring evenly, the positive electrode slurry is obtained, and then it is coated, dried, cold pressed and cut into positive electrode sheets. The surface loading of the positive electrode film is 15mg / cm 2 .

[0119]

Preparation of negative electrode sheet

[0120] Graphite, conductive carbon SP, and binder SBR are dry-mixed at a ratio of 97:1:2, deionized water is added, and the solid content is adjusted to 45%-55%. After stirring evenly, the negative electrode slurry is obtained, which is then coated, dried, cold-pressed, and cut into negative electrode sheets.

[0121] Preparation of electrolyte

[0122] In an argon atmosphere glove box, ethylene carbonate (EC) and ethyl methyl carbonate (EMC) were mixed in a volume ratio of 3:7 to obtain a solvent, LiPF6 was added to the solvent at a mass percentage of 12.5% ​​and dissolved, and stirred to obtain an electrolyte.

[0123] [Diaphragm]

[0124] Polypropylene film is used as the isolation film.

[0125]

Preparation of lithium-ion secondary batteries

[0126] The positive electrode sheet, separator, and negative electrode sheet are stacked in order, with the separator positioned between the cathode and anode to provide isolation. The cells are then wound to form a bare cell. The bare cell is then placed in an outer package, injected with the prepared electrolyte, and packaged, injected, formed, and vented to produce a lithium-ion secondary battery.

[0127] The differences between Example 2 to Example 10 and Comparative Example 1 to Comparative Example 2 and Example 1 are detailed in Table 1, and the other differences are the same as Example 1.

[0128] The relevant parameter testing methods in the above embodiments and comparative examples are as follows:

[0129] 1) Volume average particle size Dv50 test

[0130] Equipment model: Malvern 2000 (MasterSizer 2000) laser particle size analyzer, reference standard process: GB / T19077-2016 / ISO 13320:2009, specific test process: Take an appropriate amount of the sample to be tested (the sample concentration is sufficient to ensure 8%-12% obscuration), add 20ml of deionized water, and simultaneously operate the external ultraviolet (53KHz / 120W) for 5 minutes to ensure that the sample is completely dispersed. Then, the sample is measured according to the GB / T19077-2016 / ISO 13320:2009 standard.

[0131] 2) Lithium-ion secondary battery performance test

[0132] 2.1) Gram capacity test

[0133] Place the lithium-ion secondary battery at 25°C for 2 hours to ensure that the temperature of the lithium-ion secondary battery is 25°C. Charge the lithium-ion secondary battery at 0.33C at 25°C to a charge cut-off voltage of 4.4V, then continue to charge at the charge cut-off voltage until the current reaches 0.05C and the charge is cut off (where C represents the rated capacity of the lithium-ion secondary battery). Place the lithium-ion secondary battery at 25°C for 1 hour, then discharge it at 0.33C at 25°C to a discharge cut-off voltage of 1.5V. Record the total discharge capacity C0 released by the lithium-ion secondary battery, and the total discharge energy E0. Repeat the charge and discharge process twice, and divide the second charge and discharge capacity by the total weight of the actual electrode sheet positive electrode material to obtain the gram capacity of the positive electrode in the current battery cell.

[0134] 2.2) Cyclic performance test

[0135] Step 1: Place the lithium-ion secondary battery at 25°C for 30 minutes, discharge it at 0.33C to 2.5V, and place it at 25°C for 30 minutes;

[0136] Step 2: The lithium-ion secondary battery is charged at a constant current of 0.33C to 4.4V, charged at a constant voltage with a cut-off current of 0.05C, and allowed to stand at 25°C for 30 minutes. The battery is discharged at 0.33C to 2.5V, and the capacity is recorded. The battery is allowed to stand at 25°C for 30 minutes. Step 2 is repeated n times until the cycle capacity of the lithium-ion secondary battery remains at 80% of the capacity of the lithium-ion secondary battery. The cycle is stopped and the number of cycles is recorded.

[0137] 3) Characteristic substance detection

[0138] The lithium-ion secondary battery is charged to 4.4V and then disassembled in an inert atmosphere glove box. The positive electrode and negative electrode sheets are taken out respectively, and the powder on the positive electrode and negative electrode sheets is scraped off for later use. 50g of the powder of the positive electrode sheet is taken out and soaked in 100g of anhydrous ethanol, heated to 80°C, stirred and dissolved for 4h, 100mL of the supernatant is taken and dried at 100°C in vacuum to obtain the treated powder (weight is W). The treated powder is sent for XRD testing, and the test is performed at a scan rate of 1°C / min from 0 to 90°C. The specific structure of the potassium salt can be determined by peak comparison with the XRD pattern card of the standard substance. The positive and negative electrode powders, as well as the lithium-ion secondary battery electrolyte, were submitted for ICP testing. This yielded the content of each element in the positive, negative, and electrolyte, respectively. This means the potassium ion content in each of the positive, negative, and electrolytes was determined to be greater than 100 ppm. The negative electrode powder was also submitted for XPS testing, which can detect the presence of the K element. The XPS spectrum showed the presence of K peaks at all positions, indicating the presence of trace amounts of undecomposed potassium salt additives.

[0139] Table 1 Process and cycle performance parameters of the positive electrode sheets of various embodiments and comparative examples.

[0140] Note: a represents the mass fraction of the positive electrode active material in the positive electrode film layer; b represents the mass fraction of the potassium salt in the positive electrode film layer; mass ratio represents the mass ratio of the potassium salt to the positive electrode active material; voltage represents the potassium salt can decompose potassium ions under the corresponding voltage; cycle number improvement rate represents the improvement rate of the cycle number when the battery cycle capacity is maintained at 80% of the battery capacity, among which Ni65 represents LiNi 0.65 Co 0.15 Mn 0.2 O2, NCM811 represents LiNi 0.8 Co 0.1 Al 0.1 O2.

[0141] The gram capacity of Comparative Example 2 is 197 mAh / g, and the number of cycles is 1500 when the battery cycle capacity of the comparative example is maintained at 80% of the battery capacity. The gram capacity improvement rate and the cycle number improvement rate of Examples 1-3 and Examples 5-10 are the improvement rates relative to the gram capacity and cycle number of Comparative Example 2. The discharge gram capacity of Comparative Example 1 is 205 mAh / g, and the number of cycles is 1200 when the battery cycle capacity is maintained at 80% of the battery capacity. The gram capacity improvement rate and the cycle number improvement rate of Example 4 are the improvement rates relative to the gram capacity and cycle number of Comparative Example 1. It can be seen from the relevant data in Table 1 that based on Comparative Example 1 and Comparative Example 2, the positive electrode sheets of Examples 1-10 of the present application have an increased gram capacity of the positive electrode active material by 0.6%-3.6%. When the cycle capacity retention rate is 80%, the cycle numbers of Comparative Example 1 and Comparative Example 2 are 1200 and 1500, respectively. The increase in the number of battery cycles in Examples 1-4 and 5-10 is 3%-36% (i.e., 1545-2040), and the increase in the number of battery cycles in Example 4 is 21% (i.e., 1452). This indicates that the positive electrode sheet according to the embodiment of the present application can activate the dead lithium of lithium nickel cobalt manganese oxide or lithium nickel cobalt aluminum oxide by adding potassium salt additives, thereby increasing the gram capacity of lithium nickel cobalt manganese oxide or lithium nickel cobalt aluminum oxide; effectively reducing the loss of active lithium and improving the cycle stability of lithium-ion secondary batteries.

[0142] After the lithium-ion secondary battery of Example 3 was cycled for the first time, the powder of the positive electrode was subjected to an ICP test. The results showed that the K ion content in the positive electrode was 100 ppm, indicating that the positive electrode in Example 3 contained potassium ions decomposed from potassium salt.

[0143] The above is only an implementation method of the present application and does not limit the patent scope of the present application. Any equivalent structure or equivalent process transformation made using the contents of the description and drawings of this application, or directly or indirectly applied in other related technical fields, are also included in the patent protection scope of the present application.

Claims

1. A lithium-ion secondary battery, characterized in that: The invention comprises a positive electrode sheet, a negative electrode sheet and an electrolyte. The positive electrode sheet comprises a positive electrode film layer. The positive electrode film layer comprises a positive electrode active material and an additive. The positive electrode active material comprises lithium oxide. The additive comprises potassium salt. The potassium salt decomposes into potassium ions at a voltage of 3.1V-4.2V.

2. The lithium-ion secondary battery according to claim 1, wherein The potassium salt decomposes potassium ions at a voltage of 3.1V-3.9V.

3. The lithium-ion secondary battery according to claim 1 or 2, characterized in that The potassium salts include C6H5K3O7, C 12 H 10 K3Na3O 14 , one or more of K2S, KP3, CH3COOK, KN3, KNO2, KC6H5O7, K2O, K2O2, K2C2O4, K2C4O4, K2C4O6, K2C6O6, K2S2O3, K2SO3, K2CO3, and KC6H5CO2.

4. The lithium-ion secondary battery according to any one of claims 1 to 3, characterized in that: The lithium oxide includes lithium nickel cobalt manganese oxide and / or lithium nickel cobalt aluminum oxide.

5. The lithium-ion secondary battery according to any one of claims 1 to 4, characterized in that: The positive electrode film layer includes a single layer or multiple layers, wherein: At least part of the additive and the positive electrode active material are disposed in the same layer.

6. The lithium-ion secondary battery according to any one of claims 1 to 5, characterized in that: The mass ratio of the potassium salt to the positive electrode active material is (0.5-6):(91-97).

7. The lithium-ion secondary battery according to any one of claims 1 to 6, characterized in that: The mass fraction of the potassium salt in the positive electrode film layer is 0.5%-6%.

8. The lithium-ion secondary battery according to any one of claims 1 to 7, characterized in that: When the first cycle is completed, the potassium ion content in the positive electrode plate is greater than or equal to 100 PPM.

9. The lithium-ion secondary battery according to any one of claims 1 to 8, characterized in that: The volume average particle size DV50 of the potassium salt is 1 μm-30 μm.

10. The lithium-ion secondary battery according to any one of claims 1 to 9, characterized in that: The volume average particle size DV50 of the potassium salt is 3 μm-8 μm.

11. The lithium-ion secondary battery according to any one of claims 1 to 10, characterized in that: The volume average particle size DV50 of the positive electrode active material is 4 μm-6 μm.

12. The lithium-ion secondary battery according to any one of claims 1 to 11, characterized in that: The positive electrode active material includes a structural formula of LiNi x Co y M z O2 material, wherein M includes Mn or Al, x+y+z=1, 0.3≤x≤0.95, 0.03≤y≤0.3, 0.02≤z≤0.

4.

13. The lithium-ion secondary battery according to any one of claims 1 to 12, characterized in that: At the end of the formation, the negative electrode plate includes a negative electrode film layer and a solid electrolyte interface film disposed on the negative electrode film layer, and the solid electrolyte interface film includes potassium ions.

14. A positive electrode plate, characterized in that: The positive electrode plate includes a positive electrode film layer, which includes a positive electrode active material and an additive. The positive electrode active material includes lithium oxide, and the additive includes potassium salt. The potassium salt decomposes potassium ions at a voltage of 3.1V-4.2V.

15. The positive electrode sheet according to claim 14, characterized in that: The potassium salt decomposes potassium ions at a voltage of 3.1V-3.9V.

16. The positive electrode sheet according to claim 14 or 15, characterized in that: The potassium salts include C6H5K3O7, C 12 H 10 K3Na3O 14 , one or more of K2S, KP3, CH3COOK, KN3, KNO2, KC6H5O7, K2O, K2O2, K2C2O4, K2C4O4, K2C4O6, K2C6O6, K2S2O3, K2SO3, K2CO3, and KC6H5CO2.

17. The positive electrode sheet according to any one of claims 14 to 16, characterized in that: The lithium oxide includes lithium nickel cobalt manganese oxide and / or lithium nickel cobalt aluminum oxide.

18. The positive electrode sheet according to any one of claims 14 to 17, characterized in that: The mass ratio of the potassium salt to the positive electrode active material is (0.5-6):(91-97).

19. The positive electrode sheet according to any one of claims 14 to 17, characterized in that: The volume average particle size DV50 of the potassium salt is 1 μm-30 μm.

20. An electrical device, characterized in that: The invention comprises the lithium ion secondary battery according to any one of claims 1 to 13, or the positive electrode sheet according to any one of claims 14 to 19.

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