Battery, electrolyte selection method, energy storage apparatus, and electrical device

Abstract

Disclosed are a battery, an electrolyte selection method, an energy storage apparatus, and an electrical device. The battery comprises an electrode assembly and an electrolyte; the electrode assembly comprises a positive electrode sheet, a separator, and a negative electrode sheet which are sequentially stacked; at least part of the electrode assembly is infiltrated by the electrolyte, and the electrolyte comprises a lithium salt; the battery in a fully charged state is disassembled to obtain the positive electrode sheet, the positive electrode sheet and the electrolyte are assembled in a button cell, a linear sweep voltammetry test is carried out on the button cell at a potential sweep rate of 0.1 mV / s, and first peak current density a1 of the button cell satisfies the relation: 0.1 mAcm-2≤a1≤3 mAcm-2. The battery has excellent cycle performance and overcharge performance.

Description

Batteries, electrolyte selection methods, energy storage devices, and electrical equipment

[0001] This application claims priority to the Chinese patent application filed with the Patent Office of China on August 28, 2023, with application number 2023110881917 and application name “Battery, Electrolyte Selection Method, Energy Storage Device and Electrical Equipment”, and claims priority to the Chinese patent application filed with the Patent Office of China on December 29, 2023, with application number 2023118677203 and application name “Battery, Electrolyte Selection Method, Energy Storage Device and Electrical Equipment”, all contents of which are incorporated by reference into this application. Technical Field

[0002] The present application relates to the field of energy storage technology, and specifically to a battery, an electrolyte selection method, an energy storage device, and electrical equipment. Background Art

[0003] With the development of the energy storage industry and the continuous advancement of lithium-ion battery technology, wind and solar power generation and other user scenarios are placing demands on lithium-ion energy storage batteries for lower lifespan degradation and longer service life. At the same time, cell safety, the bottom line of energy storage operations, is being challenged by the increasing scale and centralization of energy storage cells. However, with the increasing energy density and cell integration of current large-scale energy storage batteries, the heat generated by the cells is increasing, making it increasingly challenging to maintain this bottom line of safety.

[0004] Summary of the Invention

[0005] In view of this, the present application provides a battery, a method for selecting an electrolyte, an energy storage device and an electrical equipment, wherein the battery has excellent cycle performance and overcharge performance.

[0006] The present application provides a battery comprising: an electrode assembly and an electrolyte, wherein the electrode assembly comprises a positive electrode sheet, a separator, and a negative electrode sheet stacked in sequence; the electrolyte at least partially infiltrates the electrode assembly, and the electrolyte comprises a lithium salt; wherein the battery in a fully charged state is disassembled to obtain the positive electrode sheet, the positive electrode sheet and the electrolyte are assembled into a button cell, and the button cell is subjected to a linear sweep voltammetry test at a potential sweep rate of 0.1 mV / s, and the first peak current density a1 of the button cell satisfies the relationship: 0.1 mA cm -2 ≤a1≤3mAcm -2 .

[0007] Furthermore, the first peak potential P1 of the button battery satisfies: 4.65V≤P1≤4.9V.

[0008] Furthermore, the second peak potential P2 of the button battery satisfies: 3.3V≤P2≤4.0V.

[0009] Furthermore, the second peak current density a2 of the button battery satisfies: 0.3 mA cm -2 ≤a2≤5mAcm -2 .

[0010] Furthermore, the ratio of the second peak current density to the first peak current density of the button battery satisfies: 0.1≤a2 / a1≤30.

[0011] Furthermore, the electrolyte further comprises a film-forming additive, and in the electrolyte, the mass fraction g of the film-forming additive satisfies the relationship: 2%≤g≤10%.

[0012] Furthermore, the film-forming additive includes at least one of vinylene carbonate, fluoroethylene carbonate, vinyl sulfate, and 1,3-propylene sultone.

[0013] Furthermore, the positive electrode sheet includes an active material layer and a current collector layer, the active material layer is arranged on the periphery of the current collector layer, the active material layer includes a binder, and in the active material layer, the mass fraction b of the binder satisfies the relationship: 2%≤b≤4%.

[0014] Furthermore, the ratio of the first peak current density a1 of the button cell to the mass fraction b of the binder satisfies the relationship: 0.025 mA cm -2 ≤a1 / b≤1mAcm -2 .

[0015] Furthermore, the ratio of the first peak current density a1 of the button cell to the unit reaction area c of the active material layer satisfies the relationship: 0.24 mA -2 ≤a1 / c≤12.32mAm -2 , wherein the unit reaction area c of the active material layer is the product of the weight g of the active material layer per unit area and the specific surface area BET of the active material layer.

[0016] Furthermore, the unit reaction area c of the active material layer satisfies the relationship: 0.1623m 2 cm -2 ≤c≤0.416m 2 cm -2 .

[0017] Furthermore, the active material layer further includes an active material, the active material is lithium iron phosphate, and the current collector layer includes aluminum.

[0018] Furthermore, the binder is polyvinylidene fluoride.

[0019] The present application also provides a method for selecting an electrolyte, the method comprising: providing a test battery, the test battery comprising a positive electrode sheet and an electrolyte; charging the test battery so that the test battery is in a fully charged state; disassembling the test battery to obtain the positive electrode sheet, using the positive electrode sheet as a working electrode and lithium metal as a counter electrode, and assembling the positive electrode sheet, lithium metal and the electrolyte into a button battery; performing a linear sweep voltammetry test on the button battery to obtain a first peak potential P1 and a first peak current density a of the button battery; and selecting a first peak potential P1 that satisfies the relationship: 4.65V≤P1≤4.9V, and a first peak current density a1 that satisfies the relationship: 0.1mAcm -2 ≤a1≤3mAcm -2 of the electrolyte.

[0020] Furthermore, the electrolyte selection method further includes: obtaining a second peak potential P2 and a second peak current density a2 of the button battery; selecting a second peak potential P2 that satisfies the relationship: 3.3V≤P2≤4.0V, and a second peak current density a2 that satisfies the relationship: 0.3mAcm -2 ≤a2≤5mAcm -2 of the electrolyte.

[0021] Furthermore, performing a linear sweep voltammetry test on the button cell to obtain a first peak potential P1 and a first peak current density a1 of the button cell includes performing a linear sweep voltammetry test on the button cell at a potential sweep rate of 0.1 mV / s.

[0022] The present application also provides an energy storage device, which includes a plurality of batteries provided in the present application, and the plurality of batteries are electrically connected to each other.

[0023] The present application also provides an electrical device, which includes: a device body and an energy storage device provided in the present application, and the energy storage device supplies power to the device body.

[0024] In the present application, when the battery is fully charged, the positive electrode sheet and the negative electrode sheet will continue to generate heat. By assembling the fully delithiated positive electrode sheet and the electrolyte in a button cell and performing linear sweep voltammetry, a characteristic first peak can be obtained, indicating that functional groups in the electrolyte, such as double bonds and cyclic structures, undergo polymerization to form a passivation film that adheres to the surface of the positive electrode sheet, passivating the high-valent transition metal oxide on the positive electrode sheet. In other words, the electrolyte has the function of passivating the positive electrode sheet. When the electrolyte and the positive electrode sheet are assembled in the battery and the battery is overcharged, the electrolyte forms a passivation film and passivates the interface between the positive electrode sheet and the electrolyte, preventing the solvent molecules in the electrolyte from directly contacting and reacting with the transition metal oxide on the positive electrode sheet, thereby reducing the generation of reaction heat, avoiding thermal runaway of the battery during overcharging, reducing the risk of thermal runaway, fire, or explosion of the battery due to overcharging, and improving the safety performance of the battery. The passivation film is an electrochemical interface film (CEI film). The generated CEI film will prevent the reaction between the electrolyte and the positive electrode to avoid generating more reaction heat, which is beneficial to improving the overcharge performance of the battery. When the first peak current density a1 of the button battery satisfies the relationship: 0.1mAcm -2 ≤a1≤3mAcm -2 If the first peak current density a1 of the button battery is within a reasonable range, then the thickness of the passivation film generated by the battery during the charging process is within a reasonable range. The passivation film can not only passivate the positive electrode plate, but also prevent the passivation film from being too thick, which increases the resistance of the active ions to move in the electrolyte, and prevents the passivation film from preventing the reaction between the electrolyte and the positive electrode plate, shortening the time for the battery to be overcharged, thereby avoiding the generation of more reaction heat and Joule heat, and preventing the diaphragm provided between the positive electrode plate and the negative electrode plate from being melted, thereby avoiding the situation of thermal runaway of the battery during the overcharging process. When the first peak current density a1 of the button battery is greater than 3mAcm -2 When the first peak current density a1 of the button battery is too large, the thickness of the passivation film generated during the charging process of the battery is too large, and the degree of passivation of the positive electrode by the electrolyte is too large. As the battery continues to charge, the impedance of the movement of active ions in the electrolyte is too large, resulting in Joule heat and increasing the heat generated by the battery during overcharging. When the first peak current density a1 of the button battery is less than 0.1 mA cm -2When the first peak current density a1 of the button battery is too small, the thickness of the passivation film formed during the charging process is too small, making it difficult for the passivation film to passivate the positive electrode plate. The positive electrode plate can continue to react with the electrolyte, generating a large amount of reaction heat. The battery has excellent cycle performance and overcharge performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following is a brief introduction to the drawings required for use in the implementation. Obviously, the drawings described below are some implementation methods of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without any creative work.

[0026] FIG1 is a schematic structural diagram of a battery according to an embodiment of the present application;

[0027] FIG2 is a schematic diagram of an exploded structure of a battery according to an embodiment of the present application;

[0028] FIG3 is a cross-sectional view of a battery according to an embodiment of the present application;

[0029] FIG4 is a cross-sectional view of a positive electrode sheet according to an embodiment of the present application;

[0030] FIG5 is a cross-sectional view of a negative electrode sheet according to an embodiment of the present application;

[0031] FIG6 is a schematic flow chart of a method for selecting an electrolyte according to an embodiment of the present application;

[0032] FIG7 is a schematic flow chart of a method for selecting an electrolyte according to another embodiment of the present application;

[0033] FIG8 is a schematic structural diagram of an energy storage device according to an embodiment of the present application;

[0034] FIG9 is a circuit block diagram of an electric device according to an embodiment of the present application;

[0035] FIG10 is a schematic structural diagram of an electrical device according to an embodiment of the present application.

[0036] Description of reference numerals:

[0037] 100-battery, 110-electrode assembly, 111-positive electrode sheet, 1111-active material layer, 1112-current collector layer, 1113-single-sided area, 112-diaphragm, 113-negative electrode sheet, 1131-negative electrode material layer, 1132-negative current collector layer, 120-end cover assembly, 130-electrical connector, 140-shell, 141-receiving chamber, 150-electrolyte, 200-energy storage device, 210-box, 211-receiving chamber, 300-electrical equipment, 310-equipment body. DETAILED DESCRIPTION

[0038] The following will be combined with the drawings in the embodiments of this application to clearly and completely describe the technical solutions in the embodiments of this application. Obviously, the embodiments described are only part of the embodiments of this application, not all of the embodiments. 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.

[0039] The terms "first," "second," and the like in the specification and claims of this application and the accompanying drawings are used to distinguish between different objects, not to describe a particular order. Furthermore, the terms "including," "having," and any variations thereof, are intended to cover non-exclusive inclusions. For example, a process, method, system, product, or apparatus comprising a series of steps or elements is not limited to the listed steps or elements but may optionally include steps or elements not listed, or may optionally include other steps or elements inherent to the process, method, product, or apparatus.

[0040] References herein to "embodiments" or "implementations" mean that a particular feature, structure, or characteristic described in connection with the embodiments or implementations may be included in at least one embodiment of the present application. The appearance of such phrases in various places in the specification does not necessarily refer to the same embodiment, nor do they constitute independent or alternative embodiments that are mutually exclusive of other embodiments. It is understood, both explicitly and implicitly, by those skilled in the art that the embodiments described herein may be combined with other embodiments.

[0041] Lithium-ion energy storage batteries often use lithium iron phosphate as the positive electrode active material. Lithium iron phosphate has the advantages of being low in oxygen release, having excellent electrochemical properties, and having good thermal stability, but its energy density is relatively low. To increase the energy density of lithium-ion energy storage batteries using lithium iron phosphate as the positive electrode active material, related technologies have improved the energy density of lithium-ion energy storage batteries through higher electrode coatings, higher cold pressing density, and larger cell capacities. These strategies have led to increasingly prominent safety issues for lithium-ion energy storage batteries. Larger cell capacities increase the heat generated by the cells, and during overcharging, the heat generated by the cells will continue to accumulate, easily causing a chain reaction in the chemical system. The continued accumulation of reaction heat increases the risk of thermal runaway, fire, and even explosion in lithium-ion energy storage batteries. In addition, as the reaction heat continues to accumulate, the separator between the positive and negative electrode plates can easily melt and rupture, causing a short circuit between the positive and negative electrode plates, which can cause the battery to experience thermal runaway, fire, or even explosion.

[0042] Referring to Figures 1 to 4, in some embodiments, the battery 100 includes: an electrode assembly 110 and an electrolyte 150, wherein the electrode assembly 110 includes a positive electrode sheet 111, a separator 112, and a negative electrode sheet 113 stacked in sequence; the electrolyte 150 at least partially infiltrates the electrode assembly 110, and the electrolyte 150 includes a lithium salt; wherein, the battery in a fully charged state is disassembled to obtain the positive electrode sheet 111, and the positive electrode sheet 111 and the electrolyte 150 are assembled into a button cell, and a linear sweep voltammetry (LSV) test is performed at a potential sweep rate of 0.1 mV / s. The first peak current density a1 of the button cell satisfies the relationship: 0.1 mA cm -2 ≤a1≤3mAcm -2 .

[0043] It can be understood that the positive electrode plate 111 is arranged on one side of the separator 112 , and the negative electrode plate 113 is arranged on the side of the separator 112 away from the positive electrode plate 111 .

[0044] It can be understood that the electrolyte 150 includes lithium salt, the battery 100 is a lithium-ion battery 100, and the electrolyte 150 reacts with the electrode assembly 110 to generate active ions, namely lithium ions.

[0045] Optionally, the positive electrode sheet 111 includes a transition metal oxide. When the electrode assembly 110 and the electrolyte 150 are assembled in the battery 100, the electrode assembly 110 reacts with the electrolyte 150 to generate lithium ions. The lithium ions are deintercalated from the positive electrode sheet 111, move through the electrolyte 150 to the negative electrode sheet 113, and then intercalate into the negative electrode sheet 113, thereby realizing the charging process of the battery 100. During the discharge process of the battery 100, the lithium ions are deintercalated from the negative electrode sheet 113, move through the electrolyte 150 to the positive electrode sheet 111, and then intercalate into the positive electrode sheet 111.

[0046] It can be understood that the battery 100 is in a fully charged state, which means that the battery 100 is charged so that the voltage of the battery 100 reaches the rated voltage and the current of the battery 100 reaches the rated current. At this time, the positive electrode plate 111 of the battery 100 is in a fully de-lithium state.

[0047] It can be understood that when the battery 100 is in a fully charged state, the positive electrode sheet 111 is disassembled, the positive electrode sheet 111 and the electrolyte 150 are assembled in a button battery, and a linear sweep voltammetry test is performed at a potential scanning rate of 0.1mV / s. It can be understood that when the battery 100 is in a fully charged state, the positive electrode sheet 111 is in a fully delithiation state, the battery 100 is disassembled, the single-sided area 1113 of the positive electrode sheet 111 and the electrolyte 150 are assembled in a button battery, and a linear sweep voltammetry test is performed at a potential scanning rate of 0.1mV / s. Voltammetry test, specifically, in the linear sweep voltammetry test, the button battery includes a working electrode, a counter electrode and an electrolyte 150, and the single-sided area 1113 of the positive electrode sheet 111 is used as the working electrode. At this time, the working electrode is in a fully delithiated state, and lithium metal is used as the counter electrode. The electrolyte 150 infiltrates the working electrode and the counter electrode. A voltage is applied to the button battery through an electrochemical workstation, and a linear sweep voltammetry test is performed on the button battery at a potential scanning rate of 0.1 mV / s to obtain the first peak potential P1 and the first peak current density a1 of the button battery.

[0048] It can be understood that the positive electrode sheet 111 includes an active material layer 1111 and a current collector layer 1112. The active material layer 1111 is disposed on one surface of the current collector layer 1112, or the active material layer 1111 is disposed on two opposite surfaces of the current collector layer 1112. The single-sided region 1113 of the positive electrode sheet 111 refers to the region of the positive electrode sheet 111 where the active material layer 1111 is disposed on only one surface of the current collector layer 1112.

[0049] It can be understood that the button battery has a first characteristic peak, indicating that when the battery 100 is in a fully charged state, functional groups in the electrolyte 150, such as double bonds and cyclic structures, undergo polymerization reactions to generate flexible organic polymers and form a passivation film attached to the surface of the positive electrode plate 111, passivating the high-valent transition metal oxide on the positive electrode plate 111, preventing the electrolyte 150 from continuing to react with the positive electrode plate 111, thereby reducing the generation of reaction heat.

[0050] It can be understood that the first peak current density a1 of the button battery can represent the degree of passivation of the positive electrode plate 111 by the electrolyte 150 when the battery 100 is fully charged, and also represents the amount of flexible organic polymer generated. The larger the value of a1, the more flexible organic polymer is generated, making the formed passivation film denser, and the greater the degree of passivation of the positive electrode plate 111 by the electrolyte 150.

[0051] Specifically, the first peak current density a1 of the button battery can be, but is not limited to, 0.1 mA cm -2 , 0.2mAcm-2 , 0.5mAcm -2 , 0.7mAcm -2 , 0.9mAcm -2 , 1.0mAcm -2 , 1.2mAcm -2 , 1.3mAcm -2 , 1.5mAcm -2 , 1.7mAcm -2 , 1.9mAcm -2 , 2.0mAcm -2 , 2.1mAcm -2 , 2.3mAcm -2 , 2.4mAcm -2 , 2.6mAcm -2 , 2.7mAcm -2 , 2.8mAcm -2 , 2.9mAcm -2 and 3mAcm -2 wait.

[0052] In this embodiment, when the battery 100 is in a fully charged state, the positive electrode plate 111 and the negative electrode plate 113 will continue to generate heat. By assembling the positive electrode plate 111 and the electrolyte 150 in a fully delithiated state into a button cell and performing linear sweep voltammetry, a characteristic first peak can be obtained, indicating that the functional groups in the electrolyte 150, such as double bonds and cyclic structures, undergo polymerization reactions to generate flexible organic polymers and form a passivation film that adheres to the surface of the positive electrode plate 111, passivating the high-valent transition metal oxide on the positive electrode plate 111. In other words, the electrolyte 150 has the function of passivating the positive electrode plate 111. When the electrolyte 150 and the positive electrode plate 111 are assembled When the battery 100 is equipped and the battery 100 is in an overcharged state, the electrolyte 150 generates a passivation film and passivates the interface between the positive electrode plate 111 and the electrolyte 150, preventing the solvent molecules in the electrolyte 150 from directly contacting and continuing to react with the transition metal oxide on the positive electrode plate 111, thereby reducing the generation of reaction heat and preventing the battery 100 from experiencing thermal runaway during overcharging. This reduces the risk of thermal runaway, fire or explosion of the battery 100 due to overcharging, and improves the safety performance of the battery 100. The passivation film is an electrochemical interface film (CEI film). The generated CEI film will prevent the electrolyte 150 from reacting with the positive electrode plate 111 and avoid generating more reaction heat, which is beneficial to improving the overcharge performance of the battery 100. When the first peak current density a1 of the button battery satisfies the relationship: 0.1 mAcm -2≤a1≤3mAcm -2 If the first peak current density a1 of the button battery is within a reasonable range, then the thickness of the passivation film formed by the electrolyte 150 during the charging process is within a reasonable range. The passivation film can both passivate the positive electrode plate 111 and prevent the passivation film from being too thick, which would increase the resistance to the movement of active ions in the electrolyte 150. This prevents the passivation film from blocking the reaction between the electrolyte 150 and the positive electrode plate 111, shortening the time it takes for the battery 100 to overcharge, thereby avoiding the generation of additional reaction heat and Joule heat, and preventing the separator 112 disposed between the positive electrode plate 111 and the negative electrode plate 113 from melting and rupturing, thereby preventing the battery 100 from experiencing thermal runaway during overcharging. In addition, the amount of flexible organic polymer generated by the electrolyte 150 is sufficient, making the formed passivation film sufficiently dense, which is conducive to improving the passivation effect of the passivation film on the high-valent transition metal oxide on the positive electrode plate 111. When the first peak current density a1 of the button battery is greater than 3 mA cm -2 When the first peak current density a1 of the button battery is too large, the thickness of the passivation film generated during the charging process of the battery 100 is too large, and the degree of passivation of the positive electrode plate 111 by the electrolyte 150 is too large. As the battery 100 continues to charge, the impedance of the movement of active ions in the electrolyte 150 is too large, resulting in Joule heat generation, which increases the heat generated by the battery 100 during overcharging. When the first peak current density a1 of the button battery is less than 0.1 mA cm -2 When the first peak current density a1 of the button battery is too small, the thickness of the passivation film formed during the charging process of the battery 100 is too small, making it difficult for the passivation film to passivate the positive electrode plate 111. The positive electrode plate 111 can continue to react with the electrolyte 150, generating a large amount of reaction heat. The battery 100 has excellent cycle performance and overcharge performance.

[0053] In the terminology of this application, "reaction heat" refers to the heat released or absorbed by the chemical reaction between active ions and transition metal oxides within the battery 100 during the charge or discharge process of the battery 100. "Joule heat" refers to the heat generated by the movement of active ions and / or electrons within the battery 100, that is, the heat generated by the flow of current within the battery 100.

[0054] Optionally, in some embodiments, the battery 100 is a cylindrical battery 100 ; in other embodiments, the battery 100 is a square column battery 100 .

[0055] Optionally, the battery 100 also includes an end cap assembly 120, an electrical connector 130 and a shell 140, the shell 140 enclosing a receiving cavity 141 to accommodate the electrode assembly 110 and the electrolyte 150, the end cap assembly 120 is electrically connected to the electrode assembly 110 through the electrical connector 130, and the end cap assembly 120 is connected to the shell 140 to close the receiving cavity 141.

[0056] In this embodiment, the housing 140 encloses the receiving cavity 141 to accommodate the electrode assembly 110 and the electrolyte 150. The electrolyte 150 is injected into the receiving cavity 141 so that the electrolyte 150 infiltrates the electrode assembly 110. The electrode assembly 110 reacts with the electrolyte 150 to achieve the release or insertion of active ions, thereby achieving the charging or discharging process of the battery 100. The opposite ends of the electrical connector 130 are electrically connected to the end cap assembly 120 and the electrode assembly 110, respectively, so that the electrical energy generated by the electrode assembly 110 is transmitted to the outside through the electrical connector 130 and the end cap assembly 120, and the external electrical energy can also be transmitted to the electrode assembly 110 through the end cap assembly 120 and the electrical connector 130, ultimately achieving the discharge and charging process of the battery 100.

[0057] In some embodiments, the first peak potential P1 of the button battery satisfies: 4.65 V ≤ P1 ≤ 4.9 V. Specifically, the value of the first peak potential P1 of the button battery can be, but is not limited to, 4.65 V, 4.68 V, 4.69 V, 4.7 V, 4.72 V, 4.74 V, 4.76 V, 4.79 V, 4.8 V, 4.82 V, 4.84 V, 4.85 V, 4.86 V, 4.87 V, 4.88 V, 4.89 V, and 4.9 V.

[0058] In this embodiment, when the first peak potential P1 of the button cell satisfies 4.65V≤P1≤4.9V, it indicates that when the battery 100 is overcharged, functional groups in the electrolyte 150, such as double bonds and cyclic structures, undergo polymerization reactions, generating flexible organic polymers that form a passivation film that adheres to the surface of the positive electrode plate 111, passivating the high-valent transition metal oxide on the positive electrode plate 111. Furthermore, the passivation film prevents the transition metal oxide on the positive electrode plate 111 from reacting with the lithium salt in the electrolyte 150, thereby reducing the generation of reaction heat and facilitating thermal runaway of the battery 100 when overcharged. In the battery 100, when the battery 100 is overcharged, the electrolyte 150 can form a passivation film to reduce the generation of reaction heat, preventing heat accumulation from causing thermal runaway of the battery 100, reducing the risk of fire or explosion of the battery 100, and improving the safety performance of the battery 100.

[0059] In some embodiments, the second peak potential P2 of the button battery satisfies: 3.3V≤P2≤4.0V. Specifically, the value of the second peak potential P2 can be, but is not limited to, 3.3V, 3.35V, 3.4V, 3.45V, 3.5V, 3.55V, 3.6V, 3.65V, 3.7V, 3.75V, 3.8V, 3.85V, 3.9V, 3.95V, and 4.0V.

[0060] It can be understood that the button battery has a second characteristic peak, indicating that when the battery 100 is fully charged, the electrolyte 150 undergoes an oxidation reaction with the positive electrode plate 111, thereby generating an inorganic salt compound with better rigidity. The generated inorganic salt compound combines with the flexible organic polymer to form a passivation film with better structural strength and adheres to the surface of the positive electrode plate 111, passivating the high-valent transition metal oxide on the positive electrode plate 111, preventing the electrolyte 150 from continuing to react with the positive electrode plate 111, thereby reducing the generation of reaction heat.

[0061] It can be understood that the peak potential of the second characteristic peak is different from that of the first characteristic peak.

[0062] In this embodiment, when the second peak potential P2 of the button cell satisfies 3.3V≤P2≤4.0V, it indicates that the electrolyte 150 in the battery 100, under overcharge, undergoes an oxidation reaction with the positive electrode plate 111, thereby generating a rigid inorganic salt compound. This inorganic salt compound then combines with the flexible organic polymer to form a passivation film with enhanced structural strength, which adheres to the surface of the positive electrode plate 111. This passivation film passesivates the high-valent transition metal oxide on the positive electrode plate 111, preventing the electrolyte 150 from further reacting with the positive electrode plate 111, thereby reducing the generation of reaction heat. Furthermore, the combination of the flexible organic polymer and the rigid inorganic salt compound imparts to the passivation film both high density and excellent structural strength, effectively preventing the transition metal oxide on the positive electrode plate 111 from reacting with the lithium salt in the electrolyte 150. This significantly reduces the generation of reaction heat and further improves the thermal runaway potential of the battery 100 under overcharge. In the battery 100, when the battery 100 is in an overcharged state, the electrolyte 150 can produce a passivation film with good structural strength and good density, so as to reduce the generation of reaction heat, avoid heat accumulation and thermal runaway of the battery 100, reduce the risk of fire or explosion of the battery 100, and improve the safety performance of the battery 100.

[0063] In some embodiments, the second peak current density a2 of the button cell satisfies: 0.3 mA cm -2 ≤a2≤5mAcm -2 Specifically, the second peak current density a2 of the button battery can be, but is not limited to, 0.3 mA cm -2 , 0.5mAcm -2 , 0.8mAcm -2 , 1.0mAcm -2 , 1.2mAcm -2 , 1.5mAcm -2 , 1.8mAcm -2 , 2.0mAcm -2 , 2.3mAcm -2 , 2.7mAcm -2 、3.0mAcm -2 , 3.2mAcm -2 , 3.4mAcm -2 、3.8mAcm -2 , 4.0mAcm -2 , 4.5mAcm -2 and 5mAcm -2 wait.

[0064] It can be understood that the second peak current density a2 of the button battery can represent the degree of passivation of the positive electrode plate 111 by the electrolyte 150 when the battery 100 is fully charged, and also represents the amount of rigid inorganic salt compounds generated. The larger the value of a2, the more rigid inorganic salt compounds are generated. The combination of rigid inorganic salt compounds and flexible organic polymers is beneficial to improving the structural strength of the formed passivation film, and the degree of passivation of the positive electrode plate 111 by the electrolyte 150 is greater.

[0065] In this embodiment, when the second peak current density a2 of the button battery meets 0.3 mA cm -2 ≤a2≤5mAcm -2 When the second peak current density a2 of the button battery is within a reasonable range, the amount of the rigid inorganic salt compound generated by the electrolyte 150 under overcharge is within a reasonable range, so that the thickness of the generated passivation film is within a reasonable range and has good structural strength. On the one hand, the passivation film can passivate the positive electrode plate 111 and prevent the passivation film from being too thick and increasing the resistance to the movement of active ions in the electrolyte 150; on the other hand, the passivation film has a high structural strength, which can prevent the passivation film from breaking due to its low structural strength, thereby ensuring the passivation effect of the passivation film on the positive electrode plate 111. When the electrolyte 150 is applied to the battery 100 and the battery 100 is overcharged, the electrolyte 150 can form a passivation film and prevent the electrolyte 150 from reacting with the positive electrode plate 111, thereby shortening the time it takes for the battery 100 to overcharge, thereby avoiding the generation of additional reaction heat and Joule heat, and preventing the separator 112 disposed between the positive electrode plate 111 and the negative electrode plate 113 from melting and rupturing, thereby preventing the battery 100 from experiencing thermal runaway during overcharging. When the second peak current density a2 of the button cell is too large, the amount of rigid inorganic salt compound generated by the electrolyte 150 during overcharge is excessive. When the rigid inorganic salt compound combines with the flexible organic polymer to form a passivation film, the resulting passivation film is too rough and loose, reducing the passivation effect of the passivation film on the positive electrode plate 111, thereby reducing the overcharge performance of the electrolyte 150. When the second peak current density a2 of the button battery is too small, the amount of rigid inorganic salt compound generated by the electrolyte 150 under overcharge is too small. When the rigid inorganic salt compound combines with the flexible organic polymer to form a passivation film, the structural strength of the generated passivation film is low, which increases the risk of the passivation film rupturing in subsequent charge and discharge cycles. As a result, the passivation film cannot guarantee the passivation effect on the positive electrode plate 111, increasing the risk of thermal runaway of the battery 100 under overcharge.

[0066] In some embodiments, the ratio of the second peak current density to the first peak current density of the button cell satisfies the following: 0.1≤a2 / a1≤30. Specifically, the value of a2 / a1 can be, but is not limited to, 0.1, 0.5, 1, 1.5, 2, 5, 6, 8, 10, 12, 13, 15, 16, 18, 20, 22, 23, 25, 26, 27, 28, 29, and 30.

[0067] In this embodiment, when the ratio of the second peak current density to the first peak current density of the button battery satisfies: 0.1≤a2 / a1≤30, the ratio of the second peak current density to the first peak current density of the button battery is within a reasonable range. When the electrolyte 150 is in an overcharged state, the amount of the flexible organic polymer and the amount of the rigid inorganic salt compound generated by the electrolyte 150 are both within a reasonable range, so that the formed passivation film has both high density and good structural strength, and has a good passivation effect on the positive electrode plate 111, thereby preventing the solvent molecules in the electrolyte 150 from directly contacting and continuing to react with the transition metal oxide on the positive electrode plate 111, thereby reducing the generation of reaction heat, avoiding thermal runaway of the battery 100 during overcharging, reducing the risk of thermal runaway, fire or explosion of the battery 100 due to overcharging, and improving the safety performance of the battery 100. When the value of a2 / a1 is too large, the amount of rigid inorganic salt compounds generated by the electrolyte 150 in an overcharge state is much greater than the amount of flexible organic polymers generated, resulting in a passivation film that is too rough and loose, reducing the passivation effect of the passivation film on the positive electrode plate 111, thereby reducing the overcharge performance of the electrolyte 150. When the value of a2 / a1 is too small, the amount of rigid inorganic salt compounds generated by the electrolyte 150 in an overcharge state is much less than the amount of flexible organic polymers generated, resulting in a weak structural strength of the passivation film, increasing the risk of the passivation film rupturing during subsequent charge and discharge cycles. As a result, the passivation film is unable to maintain its passivation effect on the positive electrode plate 111, increasing the risk of thermal runaway of the battery 100 in an overcharge state.

[0068] In some embodiments, the electrolyte further comprises a film-forming additive, wherein the mass fraction g of the film-forming additive in the electrolyte satisfies the relationship: 2% ≤ g ≤ 10%. Specifically, the mass fraction g of the film-forming additive may be, but is not limited to, 2%, 2.2%, 2.4%, 2.8%, 3%, 3.2%, 3.5%, 3.8%, 4%, 4.2%, 4.5%, 4.6%, 4.8%, 5%, 5.2%, 5.6%, 5.8%, 6%, 6.2%, 6.5%, 6.8%, 7%, 7.2%, 7.5%, 7.8%, 8%, 8.5%, 8.9%, 9%, 9.2%, 9.4%, 9.6%, and 10%.

[0069] In this embodiment, the electrolyte also includes a film-forming additive, and the mass fraction g of the film-forming additive satisfies the range of 2%≤g≤10%. The mass fraction of the film-forming additive is within a reasonable range. The film-forming additive is beneficial to promoting the formation of a passivation film and maintaining the stability of the passivation film, so that the passivation film has a better passivation effect on the positive electrode plate 111, thereby avoiding the solvent molecules in the electrolyte 150 from directly contacting and continuing to react with the transition metal oxide on the positive electrode plate 111, thereby reducing the generation of reaction heat, avoiding thermal runaway of the battery 100 during overcharging, reducing the risk of thermal runaway, fire or explosion of the battery 100 due to overcharging, and improving the safety performance of the battery 100.

[0070] Optionally, in some embodiments, the film-forming additive includes at least one of vinylene carbonate, fluoroethylene carbonate, vinyl sulfate, and 1,3-propylene sultone.

[0071] In this embodiment, at least one of vinylene carbonate, fluoroethylene carbonate, vinyl sulfate, and 1,3-propylene sultone can be used as the film-forming additive to promote the formation of a passivation film, thereby preventing the solvent molecules in the electrolyte 150 from directly contacting and continuing to react with the transition metal oxide on the positive electrode plate 111, thereby reducing the generation of reaction heat, avoiding thermal runaway of the battery 100 during overcharging, and improving the safety performance of the battery 100.

[0072] In some embodiments, the positive electrode sheet 111 includes an active material layer 1111 and a current collector layer 1112. The active material layer 1111 is disposed on the periphery of the current collector layer 1112. The active material layer 1111 includes a binder. In the active material layer 1111, the mass fraction b of the binder satisfies the relationship: 2% ≤ b ≤ 4%. Specifically, the mass fraction b of the binder can be, but is not limited to, 2%, 2.2%, 2.3%, 2.4%, 2.6%, 2.7%, 2.9%, 3%, 3.1%, 3.2%, 3.4%, 3.5%, 3.6%, 3.7%, 3.8%, 3.9%, 4%, etc.

[0073] It can be understood that the active material layer 1111 is arranged on the periphery of the current collector layer 1112. The active material layer 1111 can be arranged on one surface of the current collector layer 1112, or the active material layer 1111 can be arranged on two opposite surfaces of the current collector layer 1112.

[0074] It can be understood that the mass fraction b of the binder may be the ratio of the mass of the binder to the mass of the active material layer 1111 in the active material layer 1111 .

[0075] In this embodiment, the binder improves the bonding adhesion of other substances in the active material layer 1111 within the active material layer 1111. When the mass fraction b of the binder satisfies the relationship 2% ≤ b ≤ 4%, the mass fraction of the binder is within a reasonable range, and the binder mass ratio in the active material layer 1111 is relatively high, thereby reducing the contact area between the transition metal oxide in the active material layer 1111 and the electrolyte 150, thereby further reducing the heat of reaction between the positive electrode plate 111 and the electrolyte 150 in an overcharge state. In addition, by providing a larger amount of binder in the active material layer 1111, the reaction between the electrolyte 150 and the positive electrode plate 111 in an overcharge state can be further accelerated, thereby shortening the reaction time of the battery 100 in an overcharge state, thereby reducing the Joule heat generated in an overcharge state, and further improving the overcharge performance of the battery 100. When the mass fraction b of the binder is greater than 4%, the mass fraction of the binder is too large and the conductivity of the binder is poor. When the mass of the binder accounts for a large proportion of the mass of the active material layer 1111, the impedance of the active material layer 1111 is increased, making it difficult for electrons to move in the active material layer 1111 and difficult for active ions to be deintercalated from the active material layer 1111, thereby increasing the Joule heat of the battery 100 and the heat generated by the battery 100 in an overcharged state, thereby increasing the risk of thermal runaway, fire or explosion of the battery 100 due to excessive heat. When the mass fraction b of the binder is less than 2%, the mass fraction of the binder is too small, and the mass of the binder accounts for too small a proportion in the active material layer 1111. Then, the transition metal oxide in the active material layer 1111 still has a large contact area with the electrolyte 150. The binder is difficult to prevent the reaction between the positive electrode sheet 111 and the electrolyte 150 in an overcharged state. The longer the battery 100 continues to react in an overcharged state, the more Joule heat and reaction heat are generated, thereby increasing the risk of thermal runaway, fire or explosion of the battery 100 due to excessive heat.

[0076] In some embodiments, the binder is polyvinylidene fluoride (PVDF).

[0077] In this embodiment, the binder is polyvinylidene fluoride, which has high oxidation resistance. The binder can not only improve the bonding adhesion of other substances in the active material layer 1111 within the active material layer 1111, but also improve the oxidation resistance of the positive electrode plate 111, thereby extending the service life of the positive electrode plate 111.

[0078] In some embodiments, the active material layer 1111 further includes an active material, the active material is lithium iron phosphate, and the current collector layer 1112 includes aluminum.

[0079] In this embodiment, the active material is lithium iron phosphate. When the electrode assembly 110 and the electrolyte 150 are assembled in the battery 100, the active material lithium iron phosphate in the positive electrode plate 111 reacts with the electrolyte 150 to generate lithium ions. The lithium ions are deintercalated from the positive electrode plate 111, move through the electrolyte 150 to the negative electrode plate 113, and then intercalate into the negative electrode plate 113 to realize the charging process of the battery 100. The current collector layer 1112 includes aluminum and can collect the current generated by the active material in the active material layer 1111 to generate a larger output current. The active material is lithium iron phosphate, which makes the positive electrode plate 111 have the advantages of being difficult to release oxygen, having good electrochemical stability and good thermal stability, thereby improving the safety performance of the battery 100.

[0080] Optionally, the active material layer 1111 further includes a conductive agent, which enables the positive electrode sheet 111 to have good charge and discharge performance, facilitates the movement of electrons in the active material layer 1111 , and helps reduce the movement rate of electrons in the active material layer 1111 .

[0081] Optionally, the conductive agent includes one or more of acetylene black, conductive carbon black, carbon nanotubes, carbon fibers, graphene, and the like.

[0082] In some embodiments, the ratio of the first peak current density a1 of the button cell to the mass fraction b of the binder satisfies the relationship: 0.025 mA cm -2 ≤a1 / b≤1mAcm -2 Specifically, the ratio of the first peak current density a1 of the button cell to the mass fraction b of the binder may be, but is not limited to, 0.025 mA cm -2 , 0.03mAcm -2 , 0.05mAcm -2 , 0.08mAcm -2 , 0.1mAcm -2 , 0.15mAcm -2 , 0.18mAcm -2 , 0.2mAcm-2 , 0.25mAcm -2 , 0.28mAcm -2 、 0.35mAcm -2 , 0.38mAcm -2 , 0.42mAcm -2 , 0.50mAcm -2 , 0.55mAcm -2 , 0.58mAcm -2 , 0.62mAcm -2 , 0.68mAcm -2 , 0.72mAcm -2 , 0.86mAcm -2 , 0.89mAcm -2 , 0.92mAcm -2 , 0.95mAcm -2 , 0.97mAcm -2 and 1mAcm -2 wait.

[0083] In this embodiment, when the ratio of the first peak current density a1 of the button cell to the mass fraction b of the binder satisfies the relationship: 0.025 mA cm -2 ≤a1 / b≤1mAcm -2 When the value of the first peak current density a1 of the button battery and the value of the mass fraction b of the binder are both within a reasonable range, the thickness of the passivation film generated by the battery 100 during the charging process is within a reasonable range, the passivation film generated by the electrolyte 150 prevents the electrolyte 150 from continuing to react with the positive electrode plate 111, and the mass proportion of the binder in the active material is within a reasonable range, reducing the contact area between the transition metal oxide in the active material layer 1111 and the electrolyte 150, thereby further reducing the reaction heat between the positive electrode plate 111 and the electrolyte 150 in the overcharge state. By selecting an electrolyte 150 with a suitable first peak current density and a positive electrode plate 111 with a suitable mass fraction of the binder, the time for the electrolyte 150 to continue to react with the positive electrode plate 111 in the overcharge state of the battery 100 is shortened, reducing the Joule heat generated by the battery 100 in the overcharge state, and further improving the overcharge performance of the battery 100. When the value of a1 / b is greater than 1 mAcm -2When the first peak current density a1 of the button cell is too large, or the mass fraction b of the binder is too small, the thickness of the passivation film formed during the charging process of the battery 100 is too large. This increases the impedance to the movement of active ions in the electrolyte 150 during continued charging, resulting in Joule heat and increasing the amount of heat generated by the battery 100 during overcharging. When the mass fraction b of the binder is too small, the transition metal oxide in the active material layer 1111 still has a large contact area with the electrolyte 150, making it difficult for the binder to prevent the reaction between the positive electrode sheet 111 and the electrolyte 150 during overcharging. The longer the battery 100 continues to react during overcharging, the more Joule heat and reaction heat are generated, increasing the risk of thermal runaway, fire, or explosion in the battery 100 due to excessive heat. When the value of a1 / b is less than 0.025 mAcm -2 When the first peak current density a1 of the button cell is too small, or the mass fraction b of the binder is too large in the battery 100, the thickness of the passivation film generated during the charging process of the battery 100 is too small, making it difficult for the passivation film to passivate the positive electrode sheet 111. The positive electrode sheet 111 can still continue to react with the electrolyte 150 and generate a large amount of reaction heat. When the mass fraction b of the binder is too large, the impedance of the active material layer 1111 is increased, making it difficult for electrons to move in the active material and for active ions to be deintercalated from the active material layer 1111, thereby increasing the Joule heat of the battery 100, increasing the heat generated by the battery 100 in the overcharge state, and increasing the risk of thermal runaway, fire, or explosion of the battery 100 due to excessive heat.

[0084] In some embodiments, the ratio of the first peak current density a1 of the button cell to the unit reaction area c of the active material layer 1111 satisfies the relationship: 0.24 mA -2 ≤a1 / c≤12.32mAm -2 , wherein the unit reaction area c of the active material layer 1111 is the product of the weight g of the active material layer 1111 per unit area and the specific surface area BET of the active material layer 1111. Specifically, the ratio of the first peak current density a1 of the button cell to the unit reaction area c of the active material layer 1111 can be, but is not limited to, 0.24 mAm -2 、0.35mAm -2 、0.4mAm -2 、0.48mAm -2 、1.2mAm-2 、1.98mAm -2 、2.47mAm -2 、3.65mAm -2 、4.23mAm -2 、5.67mAm -2 、5.93mAm -2 、6.23mAm -2 、6.79mAm -2 、7.45mAm -2 、7.98mAm -2 、8.56mAm -2 、8.99mAm -2 、9.14mAm -2 、10.23mAm -2 、11.94mAm -2 and 12.32mAm -2 wait.

[0085] It can be understood that the value of a1 / c may be the degree to which the electrolyte 150 can passivate the active material layer 1111 per unit reaction area in an overcharged state.

[0086] It can be understood that the weight g of the active material layer 1111 per unit area can be obtained by taking the active material layer 1111 per unit area disposed on the surface of the current collector layer 1112, and the weight of this part of the active material layer 1111 is g.

[0087] It can be understood that the specific surface area BET of the active material layer 1111 can be the total area of ​​the active material layer 1111 .

[0088] In this embodiment, when the ratio of the first peak current density a1 of the button cell to the unit reaction area c of the active material layer 1111 satisfies the relationship: 0.24 mA -2 ≤a1 / c≤12.32mAm -2 When the electrolyte 150 forms a passivation film on the active material layer 1111 per unit reaction area within a reasonable range, the passivation film can both passivate the positive electrode plate 111 and prevent the passivation film from being too thick, thereby increasing the resistance of the active ions to move in the electrolyte 150. The passivation film prevents the electrolyte 150 from reacting with the positive electrode plate 111, shortening the time for the battery 100 to overcharge, thereby avoiding the generation of more reaction heat and Joule heat, and preventing the separator 112 disposed between the positive electrode plate 111 and the negative electrode plate 113 from being melted, thereby preventing the battery 100 from experiencing thermal runaway during overcharging. When the value of a1 / c is greater than 12.32 mAm -2When the electrolyte 150 is overcharged, the degree to which the active material layer 1111 per unit reaction area can be passivated is too great. When the battery 100 is overcharged, the passivation film formed by the electrolyte 150 on the active material layer 1111 per unit reaction area is too thick, and the impedance of the movement of active ions in the electrolyte 150 is too large, resulting in the generation of Joule heat, which increases the heat generated by the battery 100 during the overcharge process. When the value of a1 / c is less than 0.24 mA -2 When the electrolyte 150 is in an overcharged state, the degree to which the active material layer 1111 per unit reaction area can be passivated is too small, and the passivation film is difficult to passivate the positive electrode plate 111. The positive electrode plate 111 can still continue to react with the electrolyte 150 and generate more reaction heat.

[0089] In some embodiments, the unit reaction area c of the active material layer 1111 satisfies the relationship: 0.1623 m2·cm -2 ≤c≤0.416m2·cm -2 Specifically, the unit reaction area c of the active material layer 1111 may be, but is not limited to, 0.1623 m2·cm -2 , 0.17m2·cm -2 , 0.175m2·cm -2 , 0.18m2·cm -2 , 0.185m2·cm -2 , 0.2m2·cm -2 , 0.22m2·cm -2 , 0.24m2·cm -2 , 0.26m2·cm -2 , 0.28m2·cm -2 , 0.32m2·cm -2 , 0.34m2·cm -2 , 0.36m2·cm -2 , 0.38m2·cm -2 , 0.40m2·cm -2 , and 0.416m2·cm -2 wait.

[0090] In this embodiment, when the unit reaction area c of the active material layer 1111 satisfies the relationship 0.1623 m2·cm -2 ≤c≤0.416m2·cm -2When the unit reaction area c of the active material layer 1111 is within a reasonable range, the active ions can be freely released from or embedded in the active material layer 1111 during the process of charging or discharging the battery 100, thus avoiding excessive Joule heat due to excessive impedance. When the battery 100 is in an overcharged state, the contact area between the active material layer 1111 and the electrolyte 150 is within a reasonable range, and the passivation film produced by the electrolyte 150 can prevent the active material layer 1111 from continuing to react with the electrolyte 150, thus avoiding the active material layer 1111 and the electrolyte 150 from generating more reaction heat in the overcharged state, thereby increasing the risk of thermal runaway, fire or explosion of the battery 100 in the overcharged state. When the value of the unit reaction area c of the active material layer 1111 is greater than 0.416 m2·cm -2 When the unit reaction area c of the active material layer 1111 is too large, then when the battery 100 is in an overcharged state, the contact area between the active material layer 1111 and the electrolyte 150 is too large, which accelerates the reaction rate between the active material layer 1111 and the electrolyte 150, causing the active material layer 1111 and the electrolyte 150 to generate more reaction heat in the overcharged state, increasing the risk of thermal runaway, fire or explosion of the battery 100 in the overcharged state. When the value of the unit reaction area c of the active material layer 1111 is less than 0.1623 m2·cm -2 When the unit reaction area c of the active material layer 1111 is too small, when the positive electrode sheet 111 is assembled in the battery 100, the active ions are difficult to be deintercalated from the active material layer 1111, which increases the impedance of the active ions moving inside the battery 100 and reduces the cycle performance of the battery 100.

[0091] Please refer to Figures 1 to 5. Optionally, the negative electrode plate 113 includes a negative electrode material layer 1131 and a negative electrode current collector layer 1132. The negative electrode material layer 1131 is arranged on the periphery of the negative electrode current collector layer 1132. The negative electrode material layer 1131 includes a negative electrode active material, a negative electrode conductor, a thickener and a negative electrode binder.

[0092] It can be understood that the negative electrode material layer 1131 is arranged on the periphery of the negative electrode current collector layer 1132. The negative electrode material layer 1131 can be arranged on one surface of the negative electrode current collector layer 1132, or the negative electrode material layer 1131 can be arranged on two opposite surfaces of the negative electrode current collector layer 1132.

[0093] In this embodiment, the negative electrode current collector layer 1132 is used to collect the current generated by the negative active material in the negative electrode material layer 1131 to generate a higher output current. The negative electrode binder in the negative electrode current collector layer 1132 is used to bond and maintain the negative electrode current collector layer 1132, enhance the electronic contact between the negative electrode material layer 1131 and the negative electrode current collector layer 1132, and better stabilize the structure of the negative electrode plate 113. The negative electrode conductive agent enables the positive electrode plate 111 to have good charge and discharge performance, reduces the contact resistance of the negative electrode plate 113, and accelerates the movement rate of electrons in the negative electrode material layer 1131, thereby improving the charge and discharge performance of the negative electrode plate 113. The thickener is used to improve the uniformity of the various components in the negative electrode plate 113, bonding the negative electrode active material, negative electrode conductive agent, and the thickener, which is conducive to maintaining the structural integrity of the negative electrode plate 113.

[0094] Optionally, the negative electrode active material includes one or more of artificial graphite, natural graphite, petroleum coke, carbon fiber, and the like.

[0095] Optionally, the negative electrode binder includes one or more of asphalt binder, styrene-butadiene rubber (SBR), polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyvinyl alcohol (PVA), polyacrylonitrile (PAN), polyacrylic acid (PAA), polyacrylate, carboxymethyl cellulose (CMC), sodium alginate, etc.

[0096] Optionally, the negative electrode conductive agent includes one or more of acetylene black, conductive carbon black, carbon nanotubes, carbon fibers, graphene, and the like.

[0097] Optionally, the thickener includes one or more of styrene-butadiene rubber (SBR), carboxymethyl cellulose (CMC), and the like.

[0098] Referring to FIG. 6 , the present application further provides a method for selecting an electrolyte 150 , which includes:

[0099] S101 , providing a test battery, wherein the test battery includes a positive electrode sheet 111 and an electrolyte 150 .

[0100] S102: Charge the test battery to fully charge the test battery.

[0101] It can be understood that the test battery is charged so that the test battery is in a fully charged state, so that the positive electrode plate 111 is in a fully delithiation state.

[0102] S103, disassembling the test battery to obtain the positive electrode sheet 111, using the positive electrode sheet 111 as a working electrode and lithium metal as a counter electrode, and assembling the positive electrode sheet 111, lithium metal and the electrolyte 150 into a button battery.

[0103] It can be understood that the positive electrode plate 111, lithium metal and the electrolyte 150 are assembled in the button battery, and the electrolyte 150 is used to infiltrate the lithium metal and the positive electrode plate 111. The button battery can be tested by applying voltage to the button battery through an electrochemical workstation.

[0104] Furthermore, the single-sided area 1113 of the positive electrode sheet 111 is selected to be assembled in a button battery. The single-sided area 1113 of the positive electrode sheet 111 refers to an area in the positive electrode sheet 111 where the active material layer 1111 is provided on only one surface of the current collector layer 1112 .

[0105] S104 , performing a linear sweep voltammetry test on the button cell to obtain a first peak potential P1 and a first peak current density a1 of the button cell.

[0106] It can be understood that by performing a linear sweep voltammetry test on the button cell, a characteristic first peak of the button cell can be obtained, as well as a first peak potential P1 and a first peak current density a1 of the button cell. The first peak current density a1 of the button cell can represent the degree of passivation of the positive electrode plate 111 by the electrolyte 150 when the test cell is fully charged.

[0107] S105, select the first peak potential P1 that satisfies the relationship: 4.65V≤P1≤4.9V, and the first peak current density a1 that satisfies the relationship: 0.1mAcm -2 ≤a1≤3mAcm -2 of the electrolyte 150.

[0108] It can be understood that when the first peak potential P1 of the button battery satisfies the relationship 4.65V≤P1≤4.9V, it indicates that when the test battery is in a fully charged state, the functional groups in the electrolyte 150, such as double bonds and cyclic structures, undergo polymerization reactions to generate a passivation film and adhere to the surface of the positive electrode plate 111, passivating the high-valent transition metal oxide on the positive electrode plate 111, preventing the electrolyte 150 from continuing to react with the positive electrode plate 111, thereby reducing the generation of reaction heat, proving that the electrolyte 150 in the test battery can generate a passivation film and adhere to the surface of the positive electrode plate 111 when the battery 100 is in a fully charged state, and has good performance.

[0109] It can be understood that when the first peak current density a1 of the button battery satisfies the relationship: 0.1 mA cm-2 ≤a1≤3mAcm -2 When , it indicates that the thickness of the passivation film generated by the electrolyte 150 during the charging process is within a reasonable range. The passivation film can not only passivate the positive electrode plate 111, but also prevent the passivation film from being too thick and increasing the resistance of the active ions to move in the electrolyte 150. The passivation film prevents the reaction between the electrolyte 150 and the positive electrode plate 111, shortens the time for the battery 100 to be overcharged, thereby avoiding the generation of more reaction heat and Joule heat, and thus avoiding the battery 100 containing the electrolyte 150 from thermal runaway during the overcharging process.

[0110] In the method for selecting the positive electrode sheet 111 provided in this embodiment, the positive electrode sheet 111 is obtained by charging a test battery to fully charge the test battery and disassembling the test battery. The positive electrode sheet 111 and the electrolyte 150 are assembled into a button battery and the button battery is subjected to a linear sweep voltammetry test to obtain the first peak potential P1 and the first peak current density a1 of the button battery. The first peak potential P1 is determined by determining whether it satisfies the relationship: 4.65V≤P1≤4.9V and whether the first peak current density a1 satisfies the relationship: 0.1mAcm -2 ≤a1≤3mAcm -2 , in order to determine whether the electrolyte 150 can produce a flexible organic polymer to form a passivation film when the battery 100 is in a fully charged state and whether the thickness of the passivation film is within a reasonable range, thereby making the battery containing the electrolyte 150 have better overcharge performance and cycle performance. When the first peak potential P1 of the button battery is measured to meet the relationship: 4.65V≤P1≤4.9V, the first peak current density a1 meets the relationship: 0.1mAcm -2 ≤a1≤3mAcm -2 When the electrolyte 150 is selected as the electrolyte 150 with excellent performance and a dense passivation film, when the electrolyte 150 is assembled in the battery 100, the electrolyte 150 can generate a passivation film when the battery is in an overcharged state and passivate the interface between the positive electrode plate 111 and the electrolyte 150, thereby preventing the solvent molecules in the electrolyte 150 from directly contacting and continuing to react with the transition metal oxide on the positive electrode plate 111, thereby reducing the generation of reaction heat, avoiding thermal runaway of the battery 100 during overcharging, and reducing the risk of thermal runaway, fire or explosion of the battery 100 due to overcharging, thereby assembling a battery 100 with high safety performance, cycle performance and overcharge performance.

[0111] Referring to FIG. 7 , optionally, in some embodiments, the method for selecting the electrolyte further includes:

[0112] S106, obtaining the second peak potential P2 and the second peak current density a2 of the button battery; when the second peak potential P2 satisfies the relationship: 3.3V≤P2≤4.0V, the second peak current density a2 satisfies the relationship: 0.3mAcm -2 ≤a2≤5mAcm -2 of the electrolyte.

[0113] In the method for selecting the positive electrode sheet 111 provided in this embodiment, the positive electrode sheet 111 is obtained by charging a test battery to fully charge the test battery and disassembling the test battery. The positive electrode sheet 111 and the electrolyte 150 are assembled into a button battery and the button battery is subjected to a linear sweep voltammetry test to obtain the first peak potential P1, the first peak current density a1, the second peak potential P2, and the second peak current density a2 of the button battery. After determining the first peak potential and the first peak current density, it is further determined whether the second peak potential P2 satisfies the relationship: 3.3V≤P2≤4.0V, and whether the second peak current density a2 satisfies the relationship: 0.3mAcm -2 ≤a2≤5mAcm -2 The battery 100 containing the electrolyte 150 is tested to determine whether a rigid inorganic salt compound is generated in an overcharge state, thereby allowing the inorganic salt compound to combine with the organic polymer to form a passivation film with good structural strength, and the thickness of the passivation film is within a reasonable range, thereby enabling the battery containing the electrolyte 150 to have good overcharge performance and cycle performance. When the second peak potential P2 of the button battery is measured to satisfy the relationship: 3.3V≤P2≤4.0V, and the second peak current density a2 satisfies the relationship: 0.3mAcm -2 ≤a2≤5mAcm -2 When the electrolyte 150 is selected as the electrolyte 150 with excellent performance, when the electrolyte 150 is assembled in the battery 100, the electrolyte 150 can generate a passivation film with good structural strength when the battery is in an overcharge state and passivate the interface between the positive electrode plate 111 and the electrolyte 150, thereby preventing the solvent molecules in the electrolyte 150 from directly contacting and continuing to react with the transition metal oxide on the positive electrode plate 111, thereby reducing the generation of reaction heat, avoiding thermal runaway of the battery 100 during overcharging, and reducing the risk of thermal runaway, fire or explosion of the battery 100 due to overcharging, thereby assembling a battery 100 with high safety performance, cycle performance and overcharge performance.

[0114] Optionally, in some embodiments, performing a linear sweep voltammetry test on the button battery to obtain the first peak potential P1 and the first peak current density a1 of the button battery includes: performing a linear sweep voltammetry test on the button battery at a potential sweep rate of 0.1 mV / s.

[0115] In this embodiment, when the linear sweep voltammetry test is performed on the button cell at a potential sweep rate of 0.1 mV / s, the potential sweep rate is within a reasonable range, which is beneficial to improving the accuracy of the test on the button cell.

[0116] The technical solution of this application is further described below with reference to a number of embodiments.

[0117] Examples 1 to 23, Comparative Examples 1 to 4:

[0118] 1. Preparation of positive electrode sheet 111:

[0119] The positive electrode active material lithium iron phosphate, a conductive agent (conductive carbon black, SP), and a binder (polyvinylidene fluoride, PVDF) are dispersed in a solvent N-methylpyrrolidone (NMP) according to a certain mass ratio and uniformly mixed to obtain a positive electrode slurry. The positive electrode slurry is coated on a positive electrode current collector aluminum foil to form an active material layer 1111. After drying, cold pressing, slitting, and cutting, a positive electrode sheet 111 is obtained. The weight of the active material layer 1111 per unit area, the specific surface area of ​​the active material layer 1111, the unit reaction area c of the active material layer 1111, and the mass fraction b of the binder of the positive electrode sheets 111 in Examples 1 to 23 and Comparative Examples 1 to 4 are shown in Table 1. The unit reaction area c of the active material layer 1111 is the product of the weight g of the active material layer 1111 per unit area and the BET specific surface area of ​​the active material layer 1111.

[0120] 2. Preparation of negative electrode sheet 113:

[0121] The negative electrode active material artificial graphite, the negative electrode conductive agent (conductive carbon black, SP), the thickener (carboxymethyl cellulose, CMC) and the negative electrode binder (styrene-butadiene rubber, SBR) are dispersed in deionized water at a mass ratio of 96.5:0.5:1:2. The negative electrode slurry is obtained by uniform mixing. The negative electrode slurry is coated on the negative electrode current collector aluminum foil to form a negative electrode material layer 1131. After drying, cold pressing, slitting and cutting, the negative electrode sheet 113 is obtained.

[0122] 3. Preparation of diaphragm 112:

[0123] A 16 μm polyethylene film is used as the separator 112 .

[0124] 4. Preparation of electrolyte 150:

[0125] In an argon atmosphere glove box with a moisture content of less than or equal to 1 ppm, ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) are mixed in a mass ratio of 1:(0.5-2):(0.5-2), and then the dried electrolyte lithium hexafluorophosphate (LiPF6) is dissolved in the solvent and stirred until completely dissolved. At least one of vinylene carbonate (VC), fluoroethylene carbonate (FEC), vinyl sulfate (DTD), and 1,3-propane sultone (PST) is added and mixed uniformly to obtain an electrolyte 150. The raw material components of the electrolyte 150 in Examples 1 to 23 and Comparative Examples 1 to 4 are shown in Table 2.

[0126] 5. Preparation of Battery 100:

[0127] The prepared positive electrode sheet 111, separator 112, and negative electrode sheet 113 are stacked in order, and the separator 112 is arranged between the positive electrode sheet 111 and the negative electrode sheet 113. The electrode assembly 110 is obtained after winding, and the electrode assembly 110 is assembled in the receiving cavity 141. The electrode assembly 110 is electrically connected to the end cover assembly 120 through the electrical connector 130. After drying, the prepared electrolyte 150 is injected into the receiving cavity 141. The electrode assembly 110 is packaged, allowed to stand, formed, shaped, and capacity tested, and finally the battery 100 is prepared.

[0128] The batteries 100 of Examples 1 to 23 and Comparative Examples 1 to 4 were prepared according to the above method. The capacities of the electrode assemblies 110 of the batteries 100 of Examples 1 to 23 and Comparative Examples 1 to 4 are shown in Table 1.

[0129] Battery 100 performance test:

[0130] 1. The positive electrode sheets 111 and electrolyte 150 of Examples 1 to 23 and Comparative Examples 1 to 4 were assembled into button cells, and the button cells were subjected to linear sweep voltammetry testing. The specific operation was as follows:

[0131] (1) In the battery 100, the battery 100 is charged at a constant current of 0.5C to make the voltage of the battery 100 reach the rated voltage of 3.65V, and then the battery 100 is charged at a constant voltage of 3.65V to make the current of the battery 100 reach the rated current of 0.05C, so that the battery 100 is in a fully charged state. Wherein, C represents the design capacity of the battery 100, the current of 1C refers to the current intensity when the full capacity of the battery 100 is discharged in 1 hour, the current of 0.5C refers to the current intensity when the full capacity of the battery 100 is discharged in 2 hours, and the current of 0.05C refers to the current intensity when the full capacity of the battery 100 is discharged in 20 hours.

[0132] (2) When the battery 100 is fully charged, the battery 100 is disassembled, and the single-sided area 1113 of the positive electrode sheet 111 and the electrolyte 150 are assembled into a button cell. The button cell includes a working electrode, a counter electrode, and the electrolyte 150. The electrolyte 150 is soaked in the working electrode and the counter electrode. A voltage is applied to the button cell using an electrochemical workstation, with the single-sided area 1113 of the positive electrode sheet 111 serving as the working electrode and lithium metal serving as the counter electrode. The open circuit voltage of the button cell is 7 V.

[0133] (3) At 25° C., the button cell was subjected to a linear sweep voltammetry test at 0.1 mV / s to obtain a first peak potential and a first peak current density of the button cell.

[0134] The values ​​of the first peak current density a1 of the button-type batteries in Examples 1 to 23 and Comparative Examples 1 to 4 are shown in Table 1, and the values ​​of the first peak potential P1 of the button-type batteries are shown in Table 1.

[0135] 2. The capacity of Examples 1 to 23 and Comparative Examples 1 to 4 was tested. The specific operation was as follows:

[0136] (1) The battery 100 is charged at a constant power of 0.5 P to the charging cut-off voltage of the battery 100 , the initial charging capacity is recorded, and the battery 100 is left to stand for 10 minutes.

[0137] (2) The battery 100 is discharged at a constant power of 0.5P to the discharge cut-off voltage of the battery 100, and the discharge capacity of the battery 100 is recorded. P refers to the rated charge or discharge power of the battery, which is the nominal voltage U of the battery multiplied by the current density of 1C. The nominal voltage of the iron phosphate battery is 3.2V, and 0.5P refers to 0.5 times the rated power.

[0138] The capacity values ​​of the batteries 100 in Examples 1 to 23 and Comparative Examples 1 to 4 are shown in Table 1. Various performance parameters of the batteries 100 prepared in Examples 1 to 23 and Comparative Examples 1 to 4, such as the weight of the active material layer 1111 per unit area of ​​the positive electrode sheet 111, the specific surface area of ​​the active material layer 1111, the unit reaction area c of the active material layer 1111, the mass fraction b of the binder, the capacity of the electrode assembly 110, the first peak current density a1 of the button cell, the first peak potential P1 of the button cell, and the capacity of the battery 100 are also shown in Table 1.

[0139] Table 1: Performance parameter table of the battery 100 of Examples 1 to 23 and Comparative Examples 1 to 4.

[0140] Table 2: Raw material components of the electrolyte 150 of Examples 1 to 23 and Comparative Examples 1 to 4.

[0141] 2% VC+2% FEC+1% DTD+0.3% PST indicates that in the electrolyte 150 , the mass fraction of VC is 2%, the mass fraction of FEC is 2%, the mass fraction of DTD is 1%, and the mass fraction of PST is 0.3%.

[0142] Electrochemical performance test of battery 100:

[0143] 1. Cycle performance test:

[0144] Battery 100 was subjected to a charge-discharge cycle test on a charge-discharge instrument at a test temperature of 25°C, a cycle rate of 1C (i.e., both the charge rate and discharge rate were 1C), and a charging voltage of 2.5V to 3.65V. The capacity retention rate after cycling was calculated. The capacity retention rate of battery 100 cycled at 25°C was calculated as follows: Capacity retention rate after the nth cycle = (discharge capacity after the nth cycle / discharge capacity at the first cycle) × 100%.

[0145] The capacity retention rates of the batteries 100 of Examples 1 to 23 and Comparative Examples 1 to 4 after 1000 cycles at 25°C are shown in Table 3. Capacity retention rate of the battery 100 after 1000 cycles at 25°C = (discharge capacity after the 1000th cycle / discharge capacity at the first cycle) × 100%.

[0146] 2.Safety overcharge test:

[0147] The battery 100 is tested on a charge and discharge instrument, and allowed to stand for 5 hours in a temperature range of 23°C to 27°C (for example, 23°C, 25°C, 2°C, 27°C, etc.); discharged to 2.5V at 1C, charged to 3.65V at 1C and allowed to stand for 10 minutes. The battery 100 is then transferred to an overcharge test instrument for testing, and charged at a constant current of 1C until the voltage of the device reaches 5.475V or the charging time reaches 1 hour. Observe for 1 hour and record whether there is swelling, leakage, smoking, fire or explosion. The overcharge performance standards for the battery 100 are: if the battery 100 does not leak, it is a first-level standard; if the battery 100 leaks but does not smoke or thermal runaway, it is a second-level standard; if the battery 100 leaks, smokes, and has thermal runaway, but does not catch fire or explode, it is a third-level standard; if the battery 100 catches fire or explodes, it is a fourth-level standard, i.e., it does not meet the standard;

[0148] The criteria for determining thermal runaway are: 1) the test object voltage is less than or equal to 1.0V; 2) the temperature monitoring sampling frequency is 1s, and the temperature rise rate at the monitoring point is greater than or equal to 5°C / s for three consecutive times. If the battery 100 encounters both condition 1) and condition 2), the battery 100 is considered to have experienced thermal runaway.

[0149] The overcharge performance of the batteries 100 of Examples 1 to 23 and Comparative Examples 1 to 4 is shown in Table 3.

[0150] The capacity retention rates of the batteries 100 of Examples 1 to 23 and Comparative Examples 1 to 4 after 1000 cycles at 25° C. and the overcharge performance of the batteries 100 measured above are shown in Table 3.

[0151] Table 3: Electrochemical properties of the battery 100 of Examples 1 to 23 and Comparative Examples 1 to 4.

[0152] Please refer to Tables 1 to 3. It can be seen from the performance parameters and electrochemical performance parameters of the battery 100 of Examples 1 to 5, especially referring to Examples 2, 4 and 5, that when other conditions remain unchanged, as the value of the second peak current density a2 continues to increase, the value of a2 / a1 continues to increase, and the value of a1 / c continues to increase, the capacity retention rate of the battery 100 after 1000 cycles at 25°C decreases. The overcharge performance of the battery 100 of Examples 2, 4 and 5 are three-level pass, three-level pass and fail, respectively. This is because: in the batteries 100 of Examples 2 and 4, the values ​​of a2 and a2 / a1 are both within a reasonable range, while in the battery 100 of Example 5, the value of a2 is greater than 5 mA cm -2, the value of a2 / a1 is greater than 30. In other words, the values ​​of a2 and a2 / a1 are both too large, resulting in an excessive amount of rigid inorganic salt compounds generated by the electrolyte 150 under overcharge, and an excessive amount of flexible organic polymers generated. When the rigid inorganic salt compounds combine with the flexible organic polymers to form a passivation film, the generated passivation film is too rough and not dense, reducing the passivation effect of the passivation film on the positive electrode plate 111, thereby reducing the overcharge performance of the electrolyte 150, and ultimately making the capacity retention rate and overcharge performance of the battery 100 of Example 5 lower than the capacity retention rate and overcharge performance of the battery 100 of Example 2 and Example 4. It can be seen from the data of Example 1 and Example 3 that the first peak current density a1 in the battery 100 of Example 1 is 3 mA cm -2 , the value of a2 / a1 is 0.1; the first peak current density a1 in the battery 100 of Example 3 is 0.1 mA cm -2 , the value of a2 / a1 is 30.0, so that the thickness of the passivation film generated by the battery 100 of Example 1 and Example 3 during the charging process is within a reasonable range, and the structural strength, density and thickness of the passivation film generated are all within a reasonable range. The passivation film can not only passivate the positive electrode plate 111, but also prevent the passivation film from being too thick and increasing the resistance of the active ions to move in the electrolyte 150. The passivation film prevents the reaction between the electrolyte 150 and the positive electrode plate 111, shortens the time for the battery 100 to be overcharged, thereby avoiding the generation of more reaction heat and Joule heat, and preventing the separator 112 disposed between the positive electrode plate 111 and the negative electrode plate 113 from being melted, thereby avoiding the situation of thermal runaway of the battery 100 during the overcharging process, ultimately making the capacity retention rate of the battery 100 high after 1000 cycles at 25°C and the overcharge performance good, that is, the cycle performance and safety performance of the battery 100 are good.

[0153] From the performance parameters and electrochemical performance parameters of the battery 100 of Examples 3, 6 to 10, it can be seen that, under the premise that other conditions remain unchanged, as the value of the first peak current density a1 continues to increase, the value of a2 / a1 continues to decrease. Under the premise that the unit reaction area c of the active material layer 1111 remains unchanged, the value of a1 / c continues to increase, so that the capacity of the battery 100 after 1000 cycles at 25°C first increases and then decreases. The overcharge performance of the battery 100 first increases and then decreases. The overcharge performance of the battery 100 of Examples 3, 6 to 10 is three-level pass, three-level pass, two-level pass, two-level pass, three-level pass and fail, respectively. This is because, in the batteries 100 of Examples 3, 6 to 9, the values ​​of the first peak current density a1 of the button battery all satisfy the relationship: 0.1 mA cm -2 ≤a1≤3mAcm-2 , and the values ​​of a2 / a1 all satisfy 0.1≤a2 / a1≤30, the values ​​of the first peak current density a1 of the button batteries of Examples 3, 6 to 9 are within a reasonable range, so that the thickness of the passivation film generated by the battery 100 during the charging process is within a reasonable range and the values ​​of a1 increase successively, the passivation film can passivate the positive electrode sheet 111, and can also prevent the passivation film from being too thick and increasing the resistance of the active ions to move in the electrolyte 150, and the passivation film prevents the electrolyte 1 50 reacts with the positive electrode plate 111, shortening the time for the battery 100 to be overcharged, thereby avoiding the generation of more reaction heat and Joule heat, preventing the separator 112 disposed between the positive electrode plate 111 and the negative electrode plate 113 from being melted, thereby avoiding the situation of thermal runaway of the battery 100 during overcharging, and ultimately gradually improving the capacity retention rate and overcharge performance of the battery 100 after 1000 cycles at 25°C, that is, improving the cycle performance and safety performance of the battery 100. The value of the first peak current density a1 in Example 10 is greater than 3 mA cm -2 , the thickness of the passivation film formed on the battery 100 during charging is too great, and the degree of passivation of the positive electrode plate 111 by the electrolyte 150 is too great. As the battery 100 continues to charge, the impedance to the movement of active ions in the electrolyte 150 is too great, resulting in the generation of Joule heat. This increases the heat generated by the battery 100 during overcharging, reduces the capacity retention rate and overcharge performance of the battery 100 after 1000 cycles at 25°C, and thus reduces the cycle performance and safety performance of the battery 100. In addition, the batteries 100 in Comparative Examples 1 to 4 do not exhibit the characteristic first peak in the linear sweep voltammetry test. This means that when the battery 100 is overcharged, the electrolyte 150 is unable to form a passivation film, and thus cannot prevent the electrolyte 150 from continuing to react with the positive electrode plate 111, resulting in the battery 100 generating a large amount of reaction heat and Joule heat when overcharged. In Comparative Examples 1 to 4, as the capacity of the battery 100 continues to increase, the heat generated by the battery 100 in the overcharge state continues to increase, and the electrolyte 150 in Comparative Examples 1 to 4 is unable to prevent the reaction of the battery 100 in the overcharge state, causing the capacity retention rate and overcharge performance of the battery 100 after 1000 cycles at 25°C to continue to decrease. That is, the cycle performance and safety performance of the batteries 100 in Comparative Examples 1 to 4 decrease successively.

[0154] Furthermore, from the performance parameters and electrochemical performance parameters of the battery 100 of Examples 6 and 11 to 16, it can be seen that, under the premise that other conditions remain unchanged, as the mass fraction b of the binder in the active material layer 1111 continues to increase, the value of a1 / b also continues to increase, and the capacity of the battery 100 after 1000 cycles at 25°C first increases and then decreases, and the overcharge performance of the battery 100 first improves and then decreases. The overcharge performance of the battery 100 of Examples 6 and 11 to 16 are three-level pass, three-level pass, two-level pass, two-level pass, one-level pass, two-level pass and two-level pass, respectively. In Examples 12 to 15, the mass fraction b of the binder in the active material layer 1111 satisfies the relationship 2% ≤ b ≤ 4%. The mass fraction of the binder is within a reasonable range. As the mass fraction of the binder in the active material layer 1111 gradually increases, the contact area between the transition metal oxide in the active material layer 1111 and the electrolyte 150 gradually decreases, further reducing the heat of reaction between the positive electrode plate 111 and the electrolyte 150 in an overcharged state. Furthermore, by providing a larger amount of binder in the active material layer 1111, the reaction between the electrolyte 150 and the positive electrode plate 111 in an overcharged state can be further accelerated and prevented, thereby shortening the duration of the reaction in the overcharged state of the battery 100. This reduces the Joule heat generated in the overcharged state, further improving the overcharge performance of the battery 100, and ultimately gradually improving the capacity retention rate and overcharge performance of the battery 100 after 1000 cycles at 25°C. This improves the cyclability and safety of the battery 100. There is no binder in the active material layer 1111 in Example 6, and the mass fraction b of the binder in Example 11 is less than 2%, so that the transition metal oxide in the active material layer 1111 and the electrolyte 150 still have a large contact area. The binder can hardly prevent the reaction between the positive electrode plate 111 and the electrolyte 150 in the overcharge state. The longer the battery 100 continues to react in the overcharge state, the more Joule heat and reaction heat are generated. As a result, the capacity retention rate and overcharge performance of the battery 100 in Example 6 and Example 11 after 1000 cycles at 25°C are poorer than those of the battery 100 in Examples 12 to 15. Furthermore, the mass fraction b of the binder in the battery 100 of Example 16 is greater than 4%, which increases the impedance of the active material layer 1111, making it difficult for electrons to move in the active material and difficult for active ions to be deintercalated from the active material layer 1111, thereby increasing the Joule heat of the battery 100 and the heat generated by the battery 100 in an overcharge state, thereby reducing the cycle performance and overcharge performance of the battery 100.In Comparative Examples 1 to 4, no binder is provided in the active material layer 1111 of the battery 100, and the reaction time of the battery 100 in the overcharge state cannot be further shortened, resulting in poor cycle performance and overcharge performance of the batteries 100 in Comparative Examples 1 to 4.

[0155] Furthermore, from the performance parameters and electrochemical performance parameters of the battery 100 of Examples 17 to 23, it can be seen that the values ​​of the first peak current density a1, the second peak current density a2, and the value of a2 / a1 in Examples 17 to 13 are all within a reasonable range, and the values ​​of c of the battery 100 of Examples 18, 20, and 21 all meet the range of 0.1623 m2·cm -2 ≤c≤0.416m2·cm -2 , the values ​​of a1 / b all meet the range of 0.025mAcm -2 ≤a1 / b≤1mAcm -2 , and the values ​​of a1 / c all meet the range of 0.24mAm -2 ≤a1 / c≤12.32mAm -2, so that the capacity retention rate of the battery 100 of Example 18 and Example 20 after 1000 cycles at 25°C, and the overcharge performance of the battery 100 of Example 21 are passed at level 1, then the battery 100 of Example 21 has good overcharge performance. From the data of Example 17 and Example 18, it can be seen that when the mass fraction of the binder is large, the mass proportion of the binder in the active material layer 1111 is high, which reduces the contact area between the transition metal oxide in the active material layer 1111 and the electrolyte 150, and further reduces the reaction heat between the positive electrode plate 111 and the electrolyte 150 in the overcharge state. In addition, if the value of a1 / c is large, the first peak current density is large, which is conducive to improving the passivation degree of the electrolyte 150 in the overcharge state, thereby making the batteries of Example 17 and Example 18 have a high capacity retention rate. It can be seen from the data of Examples 19 to 21 that as the unit reaction area c of the active material layer 1111 continues to increase, the capacity retention rate of the battery 100 after 1000 cycles at 25°C decreases. This is because: when the battery 100 is in an overcharged state, the contact area between the active material layer 1111 and the electrolyte 150 is too large, which accelerates the reaction rate between the active material layer 1111 and the electrolyte 150, causing the active material layer 1111 and the electrolyte 150 to generate more reaction heat in the overcharged state, increasing the risk of thermal runaway, fire or explosion of the battery 100 in the overcharged state, thereby reducing the capacity retention rate of the battery 100. It can be seen from the data of Example 22 and Example 23 that when the mass proportion of the binder is too low, the thickness of the passivation film generated by the battery 100 during the charging process is too small, making it difficult for the passivation film to passivate the positive electrode plate 111. The positive electrode plate 111 can still continue to react with the electrolyte 150 to generate more reaction heat. The lower the capacity retention rate of the battery 100 after 1000 cycles at 25°C, the worse the cycle performance of the battery 100.

[0156] In summary, when the battery 100 satisfies one or more of the following conditions, the battery 100 has good cycle performance and overcharge performance, wherein the value of the first peak current density a1 satisfies the range of 0.1 mA cm -2 ≤a1≤3mAcm -2 The second peak current density a2 of the button battery satisfies: 0.3 mA cm -2 ≤a2≤5mAcm -2 The ratio of the second peak current density to the first peak current density of the button battery satisfies: 0.1≤a2 / a1≤30, the mass fraction b of the binder in the active material layer 1111 satisfies the range of 2%≤b≤4%, and the value of a1 / b satisfies the range of 0.025 mA cm -2≤a1 / b≤1mAcm -2 And the value of a1 / c satisfies the range of 0.24mAm -2 ≤a1 / c≤12.32mAm -2 When the battery 100 is cycled 1000 times at 25° C., it has a high capacity retention rate and good overcharge performance, that is, the battery 100 has good cycle performance and overcharge performance.

[0157] It can be understood that the examples of the raw material components of the electrolyte 150 in Examples 1 to 23 and Comparative Examples 1 to 4 in the embodiments of the present application are merely examples of the electrolyte 150 in each embodiment and should not be understood as limitations on the raw material components of the electrolyte 150.

[0158] Please refer to Figure 8. An embodiment of the present application further provides an energy storage device 200. The energy storage device 200 includes a plurality of batteries 100 provided in the present application, and the plurality of batteries 100 are electrically connected to each other.

[0159] In the embodiment of the present application, multiple batteries 100 are electrically connected in series, parallel, or hybrid. The batteries 100 can reduce heat generation and have excellent cycle performance and overcharge performance. The multiple batteries 100 are arranged in the energy storage device 200, which is conducive to improving the cycle performance of the energy storage device 200, reducing the reaction heat or Joule heat generated by the energy storage device 200 in the overcharge state, and avoiding thermal runaway, fire, or explosion of the energy storage device 200 due to excessive heat, thereby improving the cycle performance and safety performance of the energy storage device 200.

[0160] Optionally, the energy storage device 200 includes a box body 210 , and the box body 210 encloses a receiving cavity 211 for receiving a plurality of the batteries 100 .

[0161] 9 and 10 , an embodiment of the present application further provides an electrical device 300, comprising: a device body 310 and an energy storage device 200 provided in the present application, wherein the energy storage device 200 supplies power to the device body 310. In other words, the energy storage device 200 is electrically connected to the device body 310.

[0162] In this embodiment, the energy storage device 200 has both high cycle performance and safety performance, so that the energy storage device 200 can provide a stable power supply for the device body 310, so that the device body 310 can work stably.

[0163] The power-consuming device 300 in the embodiment of the present application may be, but is not limited to, a portable electronic device such as a mobile phone, tablet computer, laptop computer, desktop computer, smart bracelet, smart watch, e-reader, game console, or the like. It may also be a vehicle such as a car, truck, sedan, van, freight train, high-speed train, electric vehicle, or various household appliances.

[0164] It is understood that the electrical device 300 described in this embodiment is merely one form of electrical device 300 used by the energy storage device 200 and should not be construed as limiting the electrical device 300 provided herein, nor should it be construed as limiting the electrical device 300 provided in the various embodiments of this application. In the embodiment shown in FIG. 9 of this application, the electrical device 300 is an energy storage battery cabinet.

[0165] Mentioning "embodiments" and "implementation methods" in this application means that the specific features, structures or characteristics described in conjunction with the embodiments may be included in at least one embodiment of the present application. The appearance of the phrases in various places in the specification does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment that is mutually exclusive with other embodiments. It is explicitly and implicitly understood by those skilled in the art that the embodiments described in this application can be combined with other embodiments. In addition, it should be understood that the features, structures or characteristics described in the various embodiments of the present application can be arbitrarily combined to form another embodiment that does not deviate from the spirit and scope of the technical solution of the present application, unless there is a contradiction between them.

[0166] Finally, it should be noted that the above implementation modes are only used to illustrate the technical solutions of the present application and are not limiting. Although the present application has been described in detail with reference to the above preferred implementation modes, ordinary technicians in this field should understand that the technical solutions of the present application can be modified or replaced by equivalents without departing from the spirit and scope of the technical solutions of the present application.

Claims

1. A battery, wherein: The battery comprises: An electrode assembly, the electrode assembly comprising a positive electrode sheet, a separator and a negative electrode sheet stacked in sequence; and An electrolyte, wherein the electrolyte at least partially soaks the electrode assembly, and the electrolyte includes a lithium salt; The battery in a fully charged state is disassembled to obtain the positive electrode sheet, the positive electrode sheet and the electrolyte are assembled into a button cell, and the button cell is subjected to a linear scanning voltammetry test at a potential scanning rate of 0.1 mV / s. The first peak current density a1 of the button cell satisfies the relationship: 0.1 mA cm -2 ≤a1≤3mAcm -2 .

2. The battery according to claim 1, wherein The first peak potential P1 of the button battery satisfies: 4.65V≤P≤4.9V.

3. The battery according to claim 2, wherein The second peak potential P2 of the button battery satisfies: 3.3V≤P2≤4.0V.

4. The battery according to claim 3, wherein The second peak current density a2 of the button cell satisfies: 0.3 mA cm -2 ≤a2≤5mAcm -2 .

5. The battery according to claim 1, wherein The ratio of the second peak current density to the first peak current density of the button battery satisfies: 0.1≤a2 / a1≤30.

6. The battery according to any one of claims 1 to 5, wherein: The electrolyte further comprises a film-forming additive. In the electrolyte, the mass fraction g of the film-forming additive satisfies the relationship: 2%≤g≤10%.

7. The battery according to claim 6, wherein The film-forming additive includes at least one of vinylene carbonate, fluoroethylene carbonate, vinyl sulfate, and 1,3-propylene sultone.

8. The battery according to claim 1, wherein The positive electrode sheet includes an active material layer and a current collector layer. The active material layer is arranged on the periphery of the current collector layer. The active material layer includes a binder. In the active material layer, the mass fraction b of the binder satisfies the relationship: 2%≤b≤4%.

9. The battery according to claim 8, wherein The ratio of the first peak current density a1 of the button cell to the mass fraction b of the binder satisfies the relationship: 0.025 mA cm -2 ≤a1 / b≤1mAcm -2 .

10. The battery according to claim 8, wherein The ratio of the first peak current density a1 of the button cell to the unit reaction area c of the active material layer satisfies the relationship: 0.24mAm -2 ≤a1 / c≤12.32mAm -2 , wherein the unit reaction area c of the active material layer is the product of the weight g of the active material layer per unit area and the specific surface area BET of the active material layer.

11. The battery according to claim 9, wherein The unit reaction area c of the active material layer satisfies the relationship: 0.1623m 2 cm -2 ≤c≤0.416m 2 cm -2 .

12. The battery according to claim 8, wherein The active material layer further includes an active material, the active material is lithium iron phosphate, and the current collector layer includes aluminum.

13. The battery according to claim 8, wherein The binder is polyvinylidene fluoride.

14. A method for selecting an electrolyte, wherein: The method for selecting the electrolyte comprises: Providing a test battery, the test battery comprising a positive electrode plate and an electrolyte; Charging the test battery so that the test battery is in a fully charged state; Disassembling the test battery to obtain the positive electrode sheet, using the positive electrode sheet as a working electrode and lithium metal as a counter electrode, and assembling the positive electrode sheet, lithium metal and the electrolyte into a button battery; Performing a linear sweep voltammetry test on the button cell to obtain a first peak potential P1 and a first peak current density a1 of the button cell; and When the first peak potential P1 satisfies the relationship: 4.65V≤P1≤4.9V, the first peak current density a1 satisfies the relationship: 0.1mAcm -2 ≤a1≤3mAcm -2 of the electrolyte.

15. The method for selecting an electrolyte according to claim 14, wherein: The method for selecting the electrolyte further comprises: The second peak potential P2 and the second peak current density a2 of the button battery are obtained; when the second peak potential P2 satisfies the relationship: 3.3V≤P2≤4.0V, the second peak current density a2 satisfies the relationship: 0.3mAcm -2 ≤a2≤5mAcm -2 of the electrolyte.

16. The method for selecting an electrolyte according to claim 14, wherein: The performing a linear scanning voltammetry test on the button cell to obtain a first peak potential P1 and a first peak current density a1 of the button cell includes: performing a linear scanning voltammetry test on the button cell at a potential scanning rate of 0.1 mV / s.

17. An energy storage device, wherein: The energy storage device comprises a plurality of batteries as described in any one of claims 1 to 13, and the plurality of batteries are electrically connected to each other.

18. An electrical device, wherein: The electrical equipment includes: The device itself; and The energy storage device of claim 17, wherein the energy storage device supplies power to the device body.

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