Battery, Method for Selecting Electrolyte, Energy Storage Device, and Electrical Equipment

Abstract

The present application relates to a battery, a method for selecting an electrolyte, an energy storage device, and an electrical equipment. The battery includes an electrode assembly and an electrolyte. The electrode assembly includes a positive electrode sheet, a separator, and a negative electrode sheet that are sequentially stacked; at least a part of the electrode assembly is infiltrated by the electrolyte, and the electrolyte includes 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 linear sweep voltammetry testing is performed on the button cell 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<supgt;‑2< / supgt; ≤ a1 ≤ 3 mA cm<supgt;‑2< / supgt>. The battery has excellent cycle performance and overcharge performance.

Description

Technical Field

[0001] The present application relates to the technical field of energy storage, and particularly relates to a battery, a method for selecting an electrolyte, an energy storage device, and an electrical equipment. Background Art

[0002] With the development of the energy storage industry, the lithium-ion battery technology has been continuously evolving. For other user scenarios on the side of wind and solar power generation, there are requirements for lower life attenuation and longer service life for lithium-ion energy storage batteries. At the same time, as the bottom line of energy storage operation, cell safety has put forward higher requirements for the safety performance of batteries with the large-scale and centralized development of energy storage cells. However, for current large-scale energy storage batteries, as the energy density gets higher and higher, the cell integration becomes larger and larger, and the heat generated by the cells becomes higher and higher, making it more and more challenging to maintain the safety bottom line. Summary of the Invention

[0003] In view of this, the present application provides a battery, a method for selecting an electrolyte, an energy storage device, and an electrical equipment, and the battery has excellent cycle performance and overcharge performance.

[0004] The present application provides a battery, which includes: an electrode assembly and an electrolyte. The electrode assembly includes a positive electrode tab, a separator, and a negative electrode tab that are sequentially stacked; the electrolyte at least wets part of the electrode assembly, and the electrolyte includes a lithium salt; wherein, the battery in a fully charged state is disassembled to obtain the positive electrode tab, the positive electrode tab and the electrolyte are assembled into a button cell, and linear sweep voltammetry testing is performed on the button cell 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 mAcm -2 ≤a1≤3 mAcm -2 .

[0005] Further, the first peak potential P1 of the button cell satisfies: 4.65 V ≤ P1 ≤ 4.9 V.

[0006] Further, the second peak potential P2 of the button cell satisfies: 3.3 V ≤ P2 ≤ 4.0 V.

[0007] Further, the second peak current density a2 of the button cell satisfies: 0.3 mAcm -2 ≤a2≤5 mAcm -2 .

[0008] Further, the ratio of the second peak current density to the first peak current density of the button cell satisfies: 0.1 ≤ a2 / a1 ≤ 30.

[0009] Further, the electrolyte further includes a film-forming additive. In the electrolyte, the mass fraction g of the film-forming additive satisfies the relational expression: 2% ≤ g ≤ 10%.

[0010] Further, the film-forming additive includes at least one of vinylene carbonate, fluoroethylene carbonate, ethylene sulfate, and 1,3 - propanesultone.

[0011] Further, the positive electrode plate includes an active material layer and a current collector layer. The active material layer is disposed on the outer 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 relational expression: 2% ≤ b ≤ 4%.

[0012] Further, the ratio of the first peak current density a1 of the coin cell to the mass fraction b of the binder satisfies the relational expression: 0.025 mA / cm² -2 ≤ a1 / b ≤ 1 mA / cm² -2 .

[0013] Further, the ratio of the first peak current density a1 of the coin cell to the unit reaction area c of the active material layer satisfies the relational expression: 0.24 mA / m² -2 ≤ a1 / c ≤ 12.32 mA / m² -2 , where the unit reaction area c of the active material layer is the product of the weight g per unit area of the active material layer and the BET specific surface area B of the active material layer.

[0014] Further, the unit reaction area c of the active material layer satisfies the relational expression: 0.1623 m² 2 ·cm² -2 ≤ c ≤ 0.416 m² 2 ·cm² -2 .

[0015] Further, the active material layer further includes an active material. The active material is lithium iron phosphate, and the current collector layer includes aluminum.

[0016] Further, the binder is polyvinylidene fluoride.

[0017] The present application also provides a method for selecting an electrolyte. The method for selecting the electrolyte includes: providing a test battery, where the test battery includes a positive electrode sheet and an electrolyte; charging the test battery to make the test battery in a fully charged state; disassembling the test battery to obtain the positive electrode sheet, using the positive electrode sheet as a working electrode, using lithium metal as a counter electrode, and assembling the positive electrode sheet, lithium metal and the electrolyte into a button cell; performing linear sweep voltammetry testing on the button cell to obtain a first peak potential P1 and a first peak current density a of the button cell; and selecting an electrolyte when the first peak potential P1 satisfies the relationship: 4.65V ≤ P1 ≤ 4.9V and the first peak current density a1 satisfies the relationship: 0.1mAcm -2 ≤ a1 ≤ 3mAcm -2 of the electrolyte.

[0018] Further, the method for selecting the electrolyte further includes: obtaining a second peak potential P2 and a second peak current density a2 of the button cell; selecting an electrolyte when the second peak potential P2 satisfies the relationship: 3.3V ≤ P2 ≤ 4.0V and the second peak current density a2 satisfies the relationship: 0.3mAcm -2 ≤ a2 ≤ 5mAcm -2 of the electrolyte.

[0019] Further, performing linear sweep voltammetry testing on the button cell to obtain the first peak potential P1 and the first peak current density a1 of the button cell includes: performing linear sweep voltammetry testing on the button cell at a potential sweep rate of 0.1mV / s.

[0020] The present application also provides an energy storage device, where the energy storage device includes a plurality of batteries provided by the present application, and the plurality of batteries are electrically connected to each other.

[0021] The present application also provides an electrical equipment, where the electrical equipment includes: an equipment body and the energy storage device provided by the present application, and the energy storage device supplies power to the equipment body.

[0022] In this application, when the battery is in a fully charged state, the positive electrode plate and the negative electrode plate will continuously generate heat. By assembling the positive electrode plate in a fully de-lithiated state and the electrolyte into 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 reactions to form a passivation film that adheres to the surface of the positive electrode plate, passivating the high-valence transition metal oxides on the positive electrode plate. In other words, the electrolyte has the function of passivating the positive electrode plate. When the electrolyte and the positive electrode plate are assembled in the battery and the battery is in an overcharged state, the electrolyte generates a passivation film and passivates the interface between the positive electrode plate and the electrolyte, preventing the solvent molecules in the electrolyte from directly contacting the transition metal oxides on the positive electrode plate and continuing to react, thereby reducing the generation of reaction heat and avoiding thermal runaway of the battery during overcharging, reducing the risk of thermal runaway, ignition, or explosion of the battery due to overcharging, and improving the safety performance of the battery. Among them, the passivation film is an electrochemical interface film (Chemical Electrochemical Interface, CEI film). The generated CEI film will prevent the reaction between the electrolyte and the positive electrode plate and avoid the generation of more reaction heat, which is beneficial to improving the overcharging performance of the battery. When the first peak current density a1 of the button cell satisfies the relationship: 0.1 mAcm -2 ≤ a1 ≤ 3 mAcm -2 , the first peak current density a1 of the button cell is within a reasonable range, then the thickness of the passivation film generated during the charging process of the battery is within a reasonable range. The passivation film can not only passivate the positive electrode plate but also avoid the passivation film being too thick, which increases the resistance of the active ions moving in the electrolyte and prevents the passivation film from blocking the reaction between the electrolyte and the positive electrode plate, shortening the time of overcharging of the battery, thereby avoiding the generation of more reaction heat and Joule heat and preventing the separator disposed between the positive electrode plate and the negative electrode plate from being melted, thus avoiding thermal runaway of the battery during overcharging. When the first peak current density a1 of the button cell is greater than 3 mAcm -2 , the value of the first peak current density a1 of the button cell is too large, then the thickness of the passivation film generated during the charging process of the battery is too large, and the passivation degree of the electrolyte on the positive electrode plate is too large, resulting in too large an impedance for the movement of active ions in the electrolyte during the continuous charging of the battery, generating Joule heat and increasing the heat generated by the battery during overcharging. When the first peak current density a1 of the button cell is less than 0.1 mAcm -2When the value of the first peak current density a1 of the button cell is too small, the thickness of the passivation film generated during the charging process of the cell is too small, making it difficult for the passivation film to passivate the positive electrode sheet. The positive electrode sheet can still react with the electrolyte continuously to generate more reaction heat. The cell has excellent cycle performance and overcharge performance. Description of the Drawings

[0023] To more clearly illustrate the technical solutions of the embodiments of the present application, the drawings required for the implementation will be briefly introduced below. Obviously, the drawings in the following description are some embodiments of the present application. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0024] Figure 1 Structural schematic diagram of a battery according to an embodiment of the present application;

[0025] Figure 2 Exploded structural schematic diagram of a battery according to an embodiment of the present application;

[0026] Figure 3 Cross-sectional view of a battery according to an embodiment of the present application;

[0027] Figure 4 Cross-sectional view of a positive electrode sheet according to an embodiment of the present application;

[0028] Figure 5 Cross-sectional view of a negative electrode sheet according to an embodiment of the present application;

[0029] Figure 6 Flow schematic diagram of a method for selecting an electrolyte according to an embodiment of the present application;

[0030] Figure 7 Flow schematic diagram of a method for selecting an electrolyte according to another embodiment of the present application;

[0031] Figure 8 Structural schematic diagram of an energy storage device according to an embodiment of the present application;

[0032] Figure 9 Circuit block diagram of an electrical device according to an embodiment of the present application;

[0033] Figure 10 Structural schematic diagram of an electrical device according to an embodiment of the present application.

[0034] Description of the reference numerals:

[0035] 100 - Battery, 110 - Electrode assembly, 111 - Positive electrode tab, 1111 - Active material layer, 1112 - Current collector layer, 1113 - Single-sided area, 112 - Separator, 113 - Negative electrode tab, 1131 - Negative electrode material layer, 1132 - Negative current collector layer, 120 - End cap assembly, 130 - Electrical connector, 140 - Housing, 141 - Receiving cavity, 150 - Electrolyte, 200 - Energy storage device, 210 - Box body, 211 - Accommodating cavity, 300 - Electrical equipment, 310 - Equipment body. Detailed implementation manners

[0036] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present application. Apparently, the described embodiments are only a part rather than all of the embodiments of the present application. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present application without creative efforts shall fall within the protection scope of the present application.

[0037] The terms "first", "second", etc. in the specification and claims of the present application and the above-mentioned drawings are used to distinguish different objects, rather than to describe a specific order. In addition, the terms "comprising" and "having" and any variations thereof are intended to cover non-exclusive inclusion. For example, a process, method, system, product or device that includes a series of steps or units is not limited to the listed steps or units, but optionally further includes steps or units not listed, or optionally further includes other steps or units inherent to these processes, methods, products or devices.

[0038] Referring to "embodiment" or "implementation manner" herein means that a specific feature, structure or characteristic described in connection with the embodiment or implementation manner can be included in at least one embodiment of the present application. The phrase appears in various places in the specification and does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment mutually exclusive with other embodiments. Those skilled in the art will explicitly and implicitly understand that the embodiments described herein can be combined with other embodiments.

[0039] Lithium-ion energy storage batteries mostly use lithium iron phosphate as the positive electrode active material. Lithium iron phosphate has the advantages of not easy to release oxygen, good electrochemical performance and good thermal stability, but its energy density is low. In order to improve the energy density of lithium-ion energy storage batteries with lithium iron phosphate as the positive electrode active material, in the related technology, the energy density of lithium-ion energy storage batteries is improved by higher electrode coating, higher cold pressing density and larger battery cell capacity. The above strategies make the safety issues of lithium-ion energy storage batteries increasingly prominent. The larger battery cell capacity increases the heat generation of the battery cell, and during the overcharging process, the heat generated by the battery cell will continue to accumulate, which is very likely to cause a chain reaction in the chemical system. The reaction heat continues to accumulate, increasing the risk of thermal runaway, fire and even explosion of lithium-ion energy storage batteries. In addition, with the continuous accumulation of reaction heat, the diaphragm between the positive electrode plate and the negative electrode plate is easy to melt and break, causing the positive electrode plate and the negative electrode plate to short-circuit and connect, thereby causing the battery to thermal runaway, fire and even explosion.

[0040] See also 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 in a button cell, and a linear sweep voltammetry (LSV) test is performed at a potential scanning rate of 0.1 mV / s, and the first peak current density a1 of the button cell satisfies the relationship: 0.1 mAcm -2 ≤a1≤3mAcm -2 .

[0041] It can be understood that the positive electrode plate 111 is disposed on one side of the diaphragm 112 , and the negative electrode plate 113 is disposed on the side of the diaphragm 112 away from the positive electrode plate 111 .

[0042] 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.

[0043] Optionally, the positive electrode tab 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 tab 111, move through the electrolyte 150 to the negative electrode tab 113, and are intercalated into the negative electrode tab 113 to achieve the charging process of the battery 100. During the discharging process of the battery 100, the lithium ions are deintercalated from the negative electrode tab 113, move through the electrolyte 150 to the positive electrode tab 111, and are intercalated into the positive electrode tab 111.

[0044] It can be understood that the battery 100 is in a fully charged state, which can be achieved by charging the battery 100 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 tab 111 of the battery 100 is in a fully de-lithiated state.

[0045] It can be understood that when the battery 100 is in a fully charged state, the positive electrode tab 111 is disassembled, and the positive electrode tab 111 and the electrolyte 150 are assembled in a coin cell, and linear sweep voltammetry testing is performed at a potential sweep rate of 0.1 mV / s. It can be, when the battery 100 is in a fully charged state, the positive electrode tab 111 is in a fully de-lithiated state. The battery 100 is disassembled, the single-sided area 1113 of the positive electrode tab 111 and the electrolyte 150 are assembled in a coin cell, and linear sweep voltammetry testing is performed at a potential sweep rate of 0.1 mV / s. Specifically, in the linear sweep voltammetry testing, the coin cell includes a working electrode, a counter electrode, and the electrolyte 150. The single-sided area 1113 of the positive electrode tab 111 is used as the working electrode. At this time, the working electrode is in a fully de-lithiated state. A lithium metal is used as the counter electrode, and the electrolyte 150 wets the working electrode and the counter electrode. A voltage is applied to the coin cell by an electrochemical workstation, and linear sweep voltammetry testing is performed on the coin cell at a potential sweep rate of 0.1 mV / s to obtain the first peak potential P1 and the first peak current density a1 of the coin cell.

[0046] It can be understood that the positive electrode tab 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 area 1113 of the positive electrode tab 111 refers to the area of the positive electrode tab 111 where the current collector layer 1112 has an active material layer 1111 disposed on only one surface.

[0047] Understandably, the button cell 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 a polymerization reaction to generate a flexible organic polymer and form a passivation film attached to the surface of the positive electrode plate 111, passivating the high-valence transition metal oxides on the positive electrode plate 111 and preventing the electrolyte 150 from reacting further with the positive electrode plate 111, thereby reducing the generation of reaction heat.

[0048] Understandably, the first peak current density a1 of the button cell can characterize the passivation degree of the electrolyte 150 on the positive electrode plate 111 when the battery 100 is in a fully charged state, and also characterize the amount of the generated flexible organic polymer. The larger the value of a1, the more flexible organic polymer is generated, making the formed passivation film denser and the passivation degree of the electrolyte 150 on the positive electrode plate 111 greater.

[0049] Specifically, the value of the first peak current density a1 of the button cell can be, but is not limited to, 0.1 mAcm -2 , 0.2 mAcm -2 , 0.5 mAcm -2 , 0.7 mAcm -2 , 0.9 mAcm -2 , 1.0 mAcm -2 , 1.2 mAcm -2 , 1.3 mAcm -2 , 1.5 mAcm -2 , 1.7 mAcm -2 , 1.9 mAcm -2 , 2.0 mAcm -2 , 2.1 mAcm -2 , 2.3 mAcm -2 , 2.4 mAcm -2 , 2.6 mAcm -2 , 2.7 mAcm -2 , 2.8 mAcm -2 , 2.9 mAcm -2 and 3 mAcm -2 etc.

[0050] 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 continuously generate heat. By assembling the positive electrode plate 111 in a fully de-lithiated state and the electrolyte 150 into a coin cell and performing linear sweep voltammetry, a characteristic first peak can be obtained, indicating that 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-valence transition metal oxides 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 into the battery 100 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 the transition metal oxides on the positive electrode plate 111 and continuing to react, thereby reducing the generation of reaction heat and avoiding thermal runaway of the battery 100 during overcharging, reducing the risk of thermal runaway, ignition, or explosion of the battery 100 due to overcharging, and improving the safety performance of the battery 100. Among them, the passivation film is a chemical electrochemical interface (CEI) film. The generated CEI film will prevent the reaction between the electrolyte 150 and the positive electrode plate 111 and avoid the generation of more reaction heat, which is beneficial to improving the overcharge performance of the battery 100. When the first peak current density a1 of the coin cell satisfies the relationship: 0.1 mA cm -2 ≤ a1 ≤ 3 mA cm -2 , the first peak current density a1 of the coin cell is within a reasonable range, and the thickness of the passivation film generated by the electrolyte 150 during charging is within a reasonable range. The passivation film can passivate the positive electrode plate 111 and avoid the passivation film being too thick, which increases the resistance of the active ions to move in the electrolyte 150 and prevents the passivation film from preventing the reaction between the electrolyte 150 and the positive electrode plate 111, shortening the overcharge time of the battery 100, 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, thus avoiding thermal runaway of the battery 100 during overcharging. In addition, the amount of flexible organic polymer generated by the electrolyte 150 is sufficient, making the formed passivation film dense enough, which is beneficial to enhancing the passivation effect of the passivation film on the high-valence transition metal oxides on the positive electrode plate 111. When the first peak current density a1 of the coin cell is greater than 3 mA cm -2When the value of the first peak current density a1 of the button cell 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 electrolyte 150 on the positive electrode plate 111 is too large. As a result, during the continuous charging process of the battery 100, the impedance of the active ions moving in the electrolyte 150 is too large, which generates Joule heat and increases the heat generated by the battery 100 during overcharging. When the first peak current density a1 of the button cell is less than 0.1 mAcm -2 When the value of the first peak current density a1 of the button cell is too small, 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 plate 111, and the positive electrode plate 111 can still react with the electrolyte 150 to generate more reaction heat. The battery 100 has excellent cycle performance and overcharge performance.

[0051] In the terms of this application, "reaction heat" refers to the heat released or absorbed during the chemical reaction between the active ions in the battery 100 and the transition metal oxide during the charging or discharging process of the battery 100. "Joule heat" refers to the heat generated when the active ions and / or electrons move inside the battery 100, that is, the heat generated by the current flowing inside the battery 100.

[0052] Optionally, in some embodiments, the battery 100 is a cylindrical battery 100; in other embodiments, the battery 100 is a square column battery 100.

[0053] Optionally, the battery 100 further includes an end cap assembly 120, an electrical connector 130, and a housing 140. The housing 140 encloses a receiving cavity 141 to receive 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 housing 140 to close the receiving cavity 141.

[0054] In this embodiment, the housing 140 encloses the accommodation cavity 141 to accommodate the electrode assembly 110 and the electrolyte 150. The electrolyte 150 is injected into the accommodation cavity 141 so that the electrolyte 150 wets the electrode assembly 110. The electrode assembly 110 reacts with the electrolyte 150 to achieve the extraction or insertion of active ions, and then realizes 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 electrical energy from the outside can also be transmitted to the electrode assembly 110 through the end cap assembly 120 and the electrical connector 130, ultimately realizing the discharging and charging processes of the battery 100.

[0055] In some embodiments, the first peak potential P1 of the button cell satisfies: 4.65V ≤ P1 ≤ 4.9V. Specifically, the value of the first peak potential P1 of the button cell can be, but is not limited to, 4.65V, 4.68V, 4.69V, 4.7V, 4.72V, 4.74V, 4.76V, 4.79V, 4.8V, 4.82V, 4.84V, 4.85V, 4.86V, 4.87V, 4.88V, 4.89V, and 4.9V, etc.

[0056] 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 in an overcharged state, functional groups in the electrolyte 150, such as double bonds and cyclic structures, undergo a polymerization reaction to generate a flexible organic polymer and form a passivation film, which adheres to the surface of the positive electrode plate 111 and passivates the high-valent transition metal oxide on the positive electrode plate 111. Further, the transition metal oxide on the positive electrode plate 111 and the lithium salt in the electrolyte 150 cannot react due to the blocking of the passivation film, thereby reducing the generation of reaction heat and being beneficial to improving the thermal runaway situation of the battery 100 in the overcharged state. In the battery 100, when the battery 100 is in an overcharged state, the electrolyte 150 can generate a passivation film to reduce the generation of reaction heat, avoid heat accumulation and cause thermal runaway of the battery 100, reduce the risk of the battery 100 catching fire or exploding, and improve the safety performance of the battery 100.

[0057] In some embodiments, the second peak potential P2 of the button cell 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, 4.0V, etc.

[0058] It can be understood that the button cell has a second characteristic peak, indicating that when the battery 100 is in a fully charged state, 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-valence transition metal oxides on the positive electrode plate 111 and preventing the electrolyte 150 from continuing to react with the positive electrode plate 111, thereby reducing the generation of reaction heat.

[0059] It can be understood that the peak potential of the second characteristic peak is different from that of the first characteristic peak.

[0060] 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 undergoes an oxidation reaction with the positive electrode plate 111 in an overcharged state, 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-valence transition metal oxides on the positive electrode plate 111 and preventing the electrolyte 150 from continuing to react with the positive electrode plate 111, thereby reducing the generation of reaction heat. Further, the combination of the flexible organic polymer and the rigid inorganic salt compound makes the passivation film have both high density and good structural strength, which can better block the reaction between the transition metal oxides of the positive electrode plate 111 and the lithium salt in the electrolyte 150, thereby greatly reducing the generation of reaction heat and being beneficial to further improving the thermal runaway situation of the battery 100 in an overcharged state. In the battery 100, when the battery 100 is in an overcharged state, the electrolyte 150 can generate a passivation film with better structural strength and density to reduce the generation of reaction heat, avoid heat accumulation and cause thermal runaway of the battery 100, reduce the risk of the battery 100 catching fire or exploding, and improve the safety performance of the battery 100.

[0061] In some embodiments, the second peak current density a2 of the button cell satisfies: 0.3mAcm -2 ≤ a2 ≤ 5mAcm -2. Specifically, the value of the second peak current density a2 of the button cell can be, but is not limited to, 0.3 mA / cm² -2 , 0.5 mA / cm² -2 , 0.8 mA / cm² -2 , 1.0 mA / cm² -2 , 1.2 mA / cm² -2 , 1.5 mA / cm² -2 , 1.8 mA / cm² -2 , 2.0 mA / cm² -2 , 2.3 mA / cm² -2 , 2.7 mA / cm² -2 , 3.0 mA / cm² -2 , 3.2 mA / cm² -2 , 3.4 mA / cm² -2 , 3.8 mA / cm² -2 , 4.0 mA / cm² -2 , 4.5 mA / cm² -2 and 5 mA / cm² -2 etc.

[0062] It can be understood that the second peak current density a2 of the button cell can characterize the passivation degree of the electrolyte 150 on the positive electrode plate 111 when the battery 100 is fully charged, and also characterize the amount of the generated rigid inorganic salt compound. The larger the value of a2, the more the amount of the generated rigid inorganic salt compound. The rigid inorganic salt compound combines with the flexible organic polymer, which is beneficial to improving the structural strength of the formed passivation film, and then the passivation degree of the electrolyte 150 on the positive electrode plate 111 is greater.

[0063] In this embodiment, when the second peak current density a2 of the button cell satisfies 0.3 mA / cm² -2 ≤ a2 ≤ 5 mA / cm² -2When the second peak current density a2 of the button cell 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 formed 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 avoid increasing the resistance of the active ions moving in the electrolyte 150 due to the over-thick passivation film; on the other hand, the passivation film has high structural strength and can avoid the rupture of the passivation film due to 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 in an overcharged state, the electrolyte 150 can form a passivation film and prevent the reaction between the electrolyte 150 and the positive electrode plate 111, shortening the overcharging time of the battery 100, thereby avoiding the generation of more reaction heat and Joule heat, and avoiding the melting of the separator 112 disposed between the positive electrode plate 111 and the negative electrode plate 113, thus avoiding the thermal runaway of the battery 100 during overcharging. When the second peak current density a2 of the button cell is too large, the amount of the rigid inorganic salt compound generated by the electrolyte 150 under overcharge is too much. When the rigid inorganic salt compound combines with the flexible organic polymer to form a passivation film, the formed 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. When the second peak current density a2 of the button cell is too small, the amount of the rigid inorganic salt compound generated by the electrolyte 150 under overcharge is too little. When the rigid inorganic salt compound combines with the flexible organic polymer to form a passivation film, the structural strength of the formed passivation film is low, increasing the risk of rupture of the passivation film during subsequent charge and discharge cycles, so that the passivation film cannot guarantee the passivation effect on the positive electrode plate 111, increasing the risk of thermal runaway of the battery 100 in an overcharged state.

[0064] In some embodiments, the ratio of the second peak current density to the first peak current density of the button cell satisfies: 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, etc.

[0065] In this embodiment, when the ratio of the second peak current density to the first peak current density of the button cell satisfies 0.1 ≤ a2 / a1 ≤ 30, the ratio of the second peak current density to the first peak current density of the button cell is within a reasonable range. When the electrolyte 150 is in an overcharged state, the amounts of the flexible organic polymer and the rigid inorganic salt compound generated by the electrolyte 150 are both within reasonable ranges, such that the formed passivation film has both high density and good structural strength, and has a good passivation effect on the positive electrode sheet 111, thereby preventing the solvent molecules in the electrolyte 150 from directly contacting the transition metal oxide on the positive electrode sheet 111 and continuing to react, thereby reducing the generation of reaction heat and preventing the battery 100 from experiencing thermal runaway during overcharging, reducing the risk of the battery 100 catching fire or exploding due to overcharging, and improving the safety performance of the battery 100. When the value of a2 / a1 is too large, the amount of the rigid inorganic salt compound generated by the electrolyte 150 in the overcharged state is much larger than the amount of the flexible organic polymer generated, such that the formed passivation film is too rough and not dense, reducing the passivation effect of the passivation film on the positive electrode sheet 111, and thus reducing the overcharge performance of the electrolyte 150. When the value of a2 / a1 is too small, the amount of the rigid inorganic salt compound generated by the electrolyte 150 in the overcharged state is much smaller than the amount of the flexible organic polymer generated, such that the structural strength of the formed passivation film is low, increasing the risk of the passivation film cracking during subsequent charge and discharge cycles, and thus the passivation film cannot ensure the passivation effect on the positive electrode sheet 111, increasing the risk of the battery 100 experiencing thermal runaway in the overcharged state.

[0066] In some embodiments, the electrolyte further includes a film-forming additive. In the electrolyte, the mass fraction g of the film-forming additive satisfies the relational expression: 2% ≤ g ≤ 10%. Specifically, the value of 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%, etc.

[0067] In this embodiment, the electrolyte further includes a film-forming additive, and the mass fraction g of the film-forming additive satisfies the range of 2% ≤ g ≤ 10%. Then, the mass fraction of the film-forming additive is within a reasonable range. The film-forming additive is conducive to promoting the generation of the passivation film and maintaining the stability of the passivation film, so that the passivation film 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 and preventing the battery 100 from experiencing thermal runaway during overcharging, reducing the risk of thermal runaway, ignition, or explosion of the battery 100 due to overcharging, and improving the safety performance of the battery 100.

[0068] Optionally, in some embodiments, the film-forming additive includes at least one of vinylene carbonate, fluoroethylene carbonate, ethylene sulfate, and 1,3-propane sultone.

[0069] In this embodiment, at least one of vinylene carbonate, fluoroethylene carbonate, ethylene sulfate, and 1,3-propane sultone can be used as the film-forming additive to promote the generation of the 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 and preventing the battery 100 from experiencing thermal runaway during overcharging, and enhancing the safety performance of the battery 100.

[0070] In some embodiments, the positive electrode plate 111 includes an active material layer 1111 and a current collector layer 1112. The active material layer 1111 is disposed on the outer 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 value of 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%, and 4%, etc.

[0071] It can be understood that the active material layer 1111 is disposed on the outer periphery of the current collector layer 1112. It can be that 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.

[0072] Understandably, the mass fraction b of the binder can be the ratio of the mass of the binder in the active material layer 1111 to the mass of the active material layer 1111.

[0073] In this embodiment, the binder improves the adhesive 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 relational expression 2% ≤ b ≤ 4%, the mass fraction of the binder is within a reasonable range, and the mass proportion of the binder in the active material layer 1111 is relatively high, so that the contact area between the transition metal oxide in the active material layer 1111 and the electrolyte 150 is reduced, and then the reaction heat between the positive electrode plate 111 and the electrolyte 150 in the overcharge state is further reduced. In addition, by providing more binder in the active material layer 1111, the reaction between the electrolyte 150 and the positive electrode plate 111 in the overcharge state can be further accelerated, which is beneficial to shortening the reaction time of the battery 100 in the overcharge state, and then reducing the Joule heat generated in the overcharge state, and further improving the overcharge performance of the battery 100. When the value of 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 relatively large proportion of the mass in 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 for active ions to be deintercalated from the active material layer 1111, and then increasing the Joule heat of the battery 100, increasing the heat generated by the battery 100 in the overcharge state, and increasing the risks of thermal runaway, fire or explosion of the battery 100 due to excessive heat. When the value of the mass fraction b of the binder is less than 2%, the mass fraction of the binder is too small, and the proportion of the mass of the binder in the active material layer 1111 is too small. Then, there is still a large contact area between the transition metal oxide in the active material layer 1111 and the electrolyte 150, and the binder is difficult to prevent the reaction between the positive electrode plate 111 and the electrolyte 150 in the overcharge state. The longer the reaction time of the battery 100 in the overcharge state, the more Joule heat and reaction heat are generated, increasing the risks of thermal runaway, fire or explosion of the battery 100 due to excessive heat.

[0074] In some embodiments, the binder is polyvinylidene fluoride (PVDF).

[0075] In this embodiment, the binder is polyvinylidene fluoride, which has high oxidation resistance. The binder can not only improve the 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 sheet 111, thereby extending the service life of the positive electrode sheet 111.

[0076] 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.

[0077] 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 of the positive electrode sheet 111 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 are intercalated into the negative electrode sheet 113 to realize the charging process of the battery 100. The current collector layer 1112 includes aluminum, which can collect the current generated by the active material in the active material layer 1111 to generate a larger output current. The active material being lithium iron phosphate enables the positive electrode sheet 111 to have the advantages of being not easily oxygen-releasing, having good electrochemical stability and good thermal stability, thereby improving the safety performance of the battery 100.

[0078] Optionally, the active material layer 1111 further includes a conductive agent. The conductive agent enables the positive electrode sheet 111 to have good charge and discharge performance, which is beneficial to the movement of electrons in the active material layer 1111 and is beneficial to reducing the movement rate of electrons in the active material layer 1111.

[0079] Optionally, the conductive agent includes one or more of acetylene black, conductive carbon black, carbon nanotubes, carbon fibers, graphene, etc.

[0080] In some embodiments, the ratio of the first peak current density a1 of the coin cell to the mass fraction b of the binder satisfies the relationship: 0.025 mA / cm -2 ≤a1 / b≤1 mA / cm -2 . Specifically, the ratio of the first peak current density a1 of the coin cell to the mass fraction b of the binder can be, but is not limited to, 0.025 mA / cm -2 、0.03 mA / cm -2 、0.05 mA / cm -2 、0.08 mA / cm -2 、0.1 mA / cm -2 、0.15 mA / cm -2 、0.18 mA / cm -2 、0.2 mA / cm-2 , 0.25 mA / cm -2 , 0.28 mA / cm -2 , 0.35 mA / cm -2 , 0.38 mA / cm -2 , 0.42 mA / cm -2 , 0.50 mA / cm -2 , 0.55 mA / cm -2 , 0.58 mA / cm -2 , 0.62 mA / cm -2 , 0.68 mA / cm -2 , 0.72 mA / cm -2 , 0.86 mA / cm -2 , 0.89 mA / cm -2 , 0.92 mA / cm -2 , 0.95 mA / cm -2 , 0.97 mA / cm -2 and 1 mA / cm -2 etc.

[0081] 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 ≤ 1 mA / cm -2 , the values of the first peak current density a1 of the button cell and the mass fraction b of the binder are both within reasonable ranges. The thickness of the passivation film generated during the charging process of the battery 100 is within a reasonable range. The passivation film generated by the electrolyte 150 prevents the continuous reaction between the electrolyte 150 and the positive electrode plate 111. Moreover, 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, and then further reducing the reaction heat between the positive electrode plate 111 and the electrolyte 150 in the overcharged state. By selecting the electrolyte 150 with a suitable first peak current density and the positive electrode plate 111 with a suitable mass fraction of the binder, the time for the continuous reaction between the electrolyte 150 and the positive electrode plate 111 in the overcharged state of the battery 100 is shortened, the Joule heat generated by the battery 100 in the overcharged state is reduced, and further the overcharge performance of the battery 100 is improved. When the value of a1 / b is greater than 1 mA / cm -2When, in the battery 100, the value of the first peak current density a1 of the button cell is too large, or the value of the mass fraction b of the binder is too small. When the first peak current density a1 of the button cell is too large, the thickness of the passivation film generated during the charging process of the battery 100 is too large, such that during the continued charging process of the battery 100, the impedance of the movement of active ions in the electrolyte 150 is too large, resulting in the generation of Joule heat, and increasing the heat generated by the battery 100 during overcharging. When the value of the mass fraction b of the binder is too small, there is still a large contact area between the transition metal oxide in the active material layer 1111 and the electrolyte 150, and it is difficult for the binder to prevent the reaction between the positive electrode plate 111 and the electrolyte 150 in the overcharged state. The longer the reaction time of the battery 100 in the overcharged state, the more Joule heat and reaction heat are generated, increasing the risks of thermal runaway, fire, or explosion of the battery 100 due to excessive heat. When the value of a1 / b is less than 0.025 mA cm -2 When, in the battery 100, the value of the first peak current density a1 of the button cell is too small, or the value of the mass fraction b of the binder is too large. When the first peak current density a1 of the button cell is too small, the thickness of the passivation film generated during the charging process of the battery 100 is too small, such that it is difficult for the passivation film to passivate the positive electrode plate 111, and the positive electrode plate 111 can still continue to react with the electrolyte 150 to generate more reaction heat. When the value of 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 and the heat generated by the battery 100 in the overcharged state, increasing the risks of thermal runaway, fire, or explosion of the battery 100 due to excessive heat.

[0082] 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 m -2 ≤ a1 / c ≤ 12.32 mA m -2 wherein, the unit reaction area c of the active material layer 1111 is the product of the weight g per unit area of the active material layer 1111 and the BET specific surface area 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 mA m -2 、0.35 mA m -2 、0.4 mA m -2 、0.48 mA m -2 、1.2 mA m-2 , 1.98 mAm -2 , 2.47 mAm -2 , 3.65 mAm -2 , 4.23 mAm -2 , 5.67 mAm -2 , 5.93 mAm -2 , 6.23 mAm -2 , 6.79 mAm -2 , 7.45 mAm -2 , 7.98 mAm -2 , 8.56 mAm -2 , 8.99 mAm -2 , 9.14 mAm -2 , 10.23 mAm -2 , 11.94 mAm -2 and 12.32 mAm -2 etc.

[0083] It can be understood that the value of a1 / c can be the degree to which the active material layer 1111 per unit reaction area can be passivated by the electrolyte 150 in the overcharged state.

[0084] It can be understood that the weight g of the active material layer 1111 per unit area can be the weight of the active material layer 1111 per unit area provided on the surface of the current collector layer 1112, and the weight of this part of the active material layer 1111 is g.

[0085] It can be understood that the BET specific surface area of the active material layer 1111 can be the total area possessed by the active material layer 1111.

[0086] 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 mAm -2 ≤ a1 / c ≤ 12.32 mAm -2 When, the passivation film formed by the electrolyte 150 on the active material layer 1111 per unit reaction area is within a reasonable range. The passivation film can passivate the positive electrode plate 111 and avoid the passivation film being too thick to increase the resistance of the active ions moving 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 avoiding 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. When the value of a1 / c is greater than 12.32 mAm -2When the degree to which the electrolyte 150 can passivate the active material layer 1111 per unit reaction area is too large in the overcharged state, when the battery 100 is in the overcharged state, 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 and an increase in the heat generated by the battery 100 during overcharging. When the value of a1 / c is less than 0.24 mA / m -2 When the degree to which the electrolyte 150 can passivate the active material layer 1111 per unit reaction area is too small in the overcharged state, it is difficult for the passivation film to passivate the positive electrode plate 111, and the positive electrode plate 111 can still react with the electrolyte 150 to generate more reaction heat.

[0087] In some embodiments, the unit reaction area c of the active material layer 1111 satisfies the relationship: 0.1623 m 2 ·cm -2 ≤ c ≤ 0.416 m 2 ·cm -2 . Specifically, the value of the unit reaction area c of the active material layer 1111 can be, but is not limited to, 0.1623 m 2 ·cm -2 , 0.17 m 2 ·cm -2 , 0.175 m 2 ·cm -2 , 0.18 m 2 ·cm -2 , 0.185 m 2 ·cm -2 , 0.2 m 2 ·cm -2 , 0.22 m 2 ·cm -2 , 0.24 m 2 ·cm -2 , 0.26 m 2 ·cm -2 , 0.28 m 2 ·cm -2 , 0.32 m 2 ·cm -2 , 0.34 m 2 ·cm -2 , 0.36 m 2 ·cm -2 , 0.38 m 2 ·cm -2 , 0.40 m 2 ·cm -2 , and 0.416 m 2 ·cm -2 etc.

[0088] In this embodiment, when the unit reaction area c of the active material layer 1111 satisfies the relational expression 0.1623 m 2 ·cm -2 ≤ c ≤ 0.416 m 2 ·cm -2 the unit reaction area c of the active material layer 1111 is within a reasonable range, such that during the charging or discharging process of the battery 100, active ions can freely escape from or be embedded in the active material layer 1111, avoiding excessive impedance and generating too much Joule heat. 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 generated by the electrolyte 150 can prevent the active material layer 1111 from continuing to react with the electrolyte 150, avoiding the generation of more reaction heat between the active material layer 1111 and the electrolyte 150 in the overcharged state and increasing the risks 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 m 2 ·cm -2 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, accelerating the reaction rate between the active material layer 1111 and the electrolyte 150, resulting in the generation of more reaction heat between the active material layer 1111 and the electrolyte 150 in the overcharged state and increasing the risks 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 m 2 ·cm -2 the unit reaction area c of the active material layer 1111 is too small. Then, when the positive electrode plate 111 is assembled into the battery 100, it is difficult for the active ions to be deintercalated from the active material layer 1111, increasing the impedance of the active ions moving inside the battery 100 and reducing the cycle performance of the battery 100.

[0089] 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 disposed on the outer periphery of the negative electrode current collector layer 1132, and the negative electrode material layer 1131 includes a negative electrode active material, a negative electrode conductive agent, a thickening agent, and a negative electrode binder.

[0090] Understandably, the negative electrode material layer 1131 is disposed on the outer periphery of the negative electrode current collector layer 1132. It can be that the negative electrode material layer 1131 is disposed on one surface of the negative electrode current collector layer 1132. Alternatively, the negative electrode material layer 1131 is disposed on two opposite surfaces of the negative electrode current collector layer 1132.

[0091] In this embodiment, the negative electrode current collector layer 1132 is used to collect the current generated by the negative electrode active material in the negative electrode material layer 1131 to generate a larger output current. The negative electrode binder in the negative electrode current collector layer 1132 is used to bond and hold 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 thickening agent is used to improve the uniformity of the components in the negative electrode plate 113, bond the negative electrode active material, the negative electrode conductive agent, and the thickening agent, and is conducive to maintaining the integrity of the structure of the negative electrode plate 113.

[0092] Optionally, the negative electrode active material includes one or more of artificial graphite, natural graphite, petroleum coke, carbon fiber, etc.

[0093] 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.

[0094] Optionally, the negative electrode conductive agent includes one or more of acetylene black, conductive carbon black, carbon nanotubes, carbon fiber, graphene, etc.

[0095] Optionally, the thickening agent includes one or more of styrene-butadiene rubber (SBR), carboxymethyl cellulose (CMC), etc.

[0096] Please refer to Figure 6 , this application also provides a method for selecting an electrolyte 150. The method for selecting the electrolyte 150 includes:

[0097] S101, providing a test battery, where the test battery includes a positive electrode plate 111 and an electrolyte 150.

[0098] S102, charging the test battery so that the test battery is in a fully charged state.

[0099] Understandably, the test battery is charged so that the test battery is in a fully charged state, and the positive electrode sheet 111 is in a fully de-lithiated state.

[0100] S103. Disassemble the test battery to obtain the positive electrode sheet 111. Using the positive electrode sheet 111 as the working electrode and lithium metal as the counter electrode, assemble the positive electrode sheet 111, lithium metal, and the electrolyte 150 into a button cell.

[0101] Understandably, when the positive electrode sheet 111, lithium metal, and the electrolyte 150 are assembled into the button cell, the electrolyte 150 is used to infiltrate the lithium metal and the positive electrode sheet 111. By applying a voltage to the button cell through an electrochemical workstation, the button cell can be tested.

[0102] Furthermore, select the single-sided area 1113 of the positive electrode sheet 111 to be assembled into the button cell. The single-sided area 1113 of the positive electrode sheet 111 refers to the area of the positive electrode sheet 111 where the current collector layer 1112 has an active material layer 1111 disposed on only one surface.

[0103] S104. Perform a linear sweep voltammetry test on the button cell to obtain the first peak potential P1 and the first peak current density a1 of the button cell.

[0104] Understandably, by performing a linear sweep voltammetry test on the button cell, the characteristic first peak of the button cell can be obtained, and the first peak potential P1 and the first peak current density a1 of the button cell can be obtained. Among them, the first peak current density a1 of the button cell can characterize the passivation degree of the electrolyte 150 on the positive electrode sheet 111 when the test battery is in a fully charged state.

[0105] S105. Select the electrolyte 150 when the first peak potential P1 satisfies the relational expression: 4.65V ≤ P1 ≤ 4.9V, and the first peak current density a1 satisfies the relational expression: 0.1mAcm -2 ≤ a1 ≤ 3mAcm -2 of the electrolyte 150.

[0106] Understandably, when the first peak potential P1 of the button cell satisfies the relation 4.65V ≤ P1 ≤ 4.9V, it indicates that when the test cell is in a fully charged state, functional groups such as double bonds and cyclic structures in the electrolyte 150 undergo a polymerization reaction to form a passivation film that adheres to the surface of the positive electrode plate 111, passivating the high-valence transition metal oxide on the positive electrode plate 111 and preventing the electrolyte 150 from reacting further with the positive electrode plate 111, thereby reducing the generation of reaction heat, demonstrating that the electrolyte 150 in the test cell 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.

[0107] Understandably, when the first peak current density a1 of the button cell satisfies the relation: 0.1mAcm -2 ≤ a1 ≤ 3mAcm -2 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, which increases the resistance to the movement of active ions 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 undergo overcharging, thereby avoiding the generation of more reaction heat and Joule heat, and thus preventing the battery 100 containing the electrolyte 150 from experiencing thermal runaway during overcharging.

[0108] In the method for selecting the positive electrode plate 111 provided in this embodiment, the test cell is charged to make the test cell in a fully charged state, and the test cell is disassembled to obtain the positive electrode plate 111. By assembling the positive electrode plate 111 and the electrolyte 150 into a button cell and performing linear sweep voltammetry testing on the button cell, the first peak potential P1 and the first peak current density a1 of the button cell are obtained. By determining whether the first peak potential P1 satisfies the relation: 4.65V ≤ P1 ≤ 4.9V, and whether the first peak current density a1 satisfies the relation: 0.1mAcm -2 ≤ a1 ≤ 3mAcm -2 it is obtained whether the electrolyte 150 can generate a flexible organic polymer to form a passivation film and the thickness of the generated passivation film is within a reasonable range when the battery 100 is in a fully charged state, thereby enabling the battery containing the electrolyte 150 to have good overcharge performance and cycling performance. When it is measured that the first peak potential P1 of the button cell satisfies the relation: 4.65V ≤ P1 ≤ 4.9V, and the first peak current density a1 satisfies the relation: 0.1mAcm -2 ≤ a1 ≤ 3mAcm -2When the electrolyte 150 is selected as the electrolyte 150 with excellent performance, the passivation film is relatively dense; when the electrolyte 150 is assembled into 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, avoiding the direct contact between the solvent molecules in the electrolyte 150 and the transition metal oxide on the positive electrode plate 111 and continuing to react, thereby reducing the generation of reaction heat, avoiding the thermal runaway of the battery 100 during overcharging, and reducing the risk of thermal runaway, ignition or explosion of the battery 100 due to overcharging, thereby assembling a battery 100 with high safety performance, cycle performance and overcharge performance.

[0109] Please refer to Figure 7 , optionally, in some embodiments, the method for selecting the electrolyte further includes:

[0110] S106, obtaining the second peak potential P2 and the second peak current density a2 of the button cell; when the second peak potential P2 satisfies the relational expression: 3.3V ≤ P2 ≤ 4.0V, the second peak current density a2 satisfies the relational expression: 0.3mAcm -2 ≤ a2 ≤ 5mAcm -2 of the electrolyte.

[0111] In the method for selecting the positive electrode plate 111 provided in this embodiment, the test battery is charged to make the test battery in a fully charged state, and the test battery is disassembled to obtain the positive electrode plate 111. By assembling the positive electrode plate 111 and the electrolyte 150 into a button cell and performing linear sweep voltammetry testing on the button cell, 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 cell are obtained. After determining the first peak potential and the first peak current density, it is further determined whether the second peak potential P2 satisfies the relational expression: 3.3V ≤ P2 ≤ 4.0V, and whether the second peak current density a2 satisfies the relational expression: 0.3mAcm -2 ≤ a2 ≤ 5mAcm -2 to obtain whether a rigid inorganic salt compound is generated in the overcharged state of the battery 100 containing the electrolyte 150, so that the inorganic salt compound combines with the organic polymer to form a passivation film with better structural strength, and the thickness of the passivation film is within a reasonable range, thereby enabling the battery containing the electrolyte 150 to have better overcharge performance and cycle performance. When the second peak potential P2 of the button cell is measured to satisfy the relational expression: 3.3V ≤ P2 ≤ 4.0V, and the second peak current density a2 satisfies the relational expression: 0.3mAcm -2 ≤ a2 ≤ 5mAcm -2When selecting the electrolyte 150 with excellent performance, when the electrolyte 150 is assembled into the battery 100, the electrolyte 150 can generate a passivation film with good structural strength and passivate the interface between the positive electrode plate 111 and the electrolyte 150 when the battery is in an overcharged state, avoiding direct contact between the solvent molecules in the electrolyte 150 and the transition metal oxide on the positive electrode plate 111 and continuing to react, thereby reducing the generation of reaction heat, avoiding the occurrence of thermal runaway during the overcharging of the battery 100, and reducing the risk of thermal runaway, ignition or explosion of the battery 100 due to overcharging. Thus, a battery 100 with high safety performance, cycle performance and overcharging performance is assembled.

[0112] Optionally, in some embodiments, the linear sweep voltammetry test on the coin cell to obtain the first peak potential P1 and the first peak current density a1 of the coin cell includes: performing a linear sweep voltammetry test on the coin cell at a potential sweep rate of 0.1 mV / s.

[0113] In this embodiment, when performing a linear sweep voltammetry test on the coin 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 coin cell.

[0114] The technical solution of the present application will be further described in multiple embodiments below.

[0115] Examples 1 to 23, Comparative Examples 1 to 4:

[0116] 1. Preparation of the positive electrode plate 111:

[0117] The positive active material lithium iron phosphate, the conductive agent (conductive carbon black, SP), and the binder (polyvinylidene fluoride, PVDF) are dispersed in the solvent N-methylpyrrolidone (NMP) according to a certain mass ratio and mixed evenly to obtain a positive electrode paste; the positive electrode paste is coated on the positive electrode current collector aluminum foil to form an active material layer 1111. After drying, cold pressing, slitting, and cutting, the positive electrode plate 111 is obtained. Among them, 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 in Examples 1 to 23 and Comparative Examples 1 to 4 are shown in Table 1. Among them, 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.

[0118] 2. Preparation of the negative electrode plate 113:

[0119] Disperse artificial graphite as the negative electrode active material, a negative electrode conductive agent (conductive carbon black, SP), a thickening agent (carboxymethyl cellulose, CMC), and a negative electrode binder (styrene-butadiene rubber, SBR) in deionized water at a mass ratio of 96.5:0.5:1:2, and obtain a negative electrode slurry by mixing evenly. Coat the negative electrode slurry on an aluminum foil negative electrode current collector to form a negative electrode material layer 1131. After drying, cold pressing, slitting, and cutting, obtain the negative electrode plate 113.

[0120] 3. Preparation of the separator 112:

[0121] Use a 16-μm polyethylene film as the separator 112.

[0122] 4. Preparation of the electrolyte 150:

[0123] In an argon atmosphere glove box with a water content less than or equal to 1 ppm, mix ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) at a mass ratio of 1:(0.5 - 2):(0.5 - 2). Then dissolve dry lithium hexafluorophosphate (LiPF6) electrolyte into the solvent, stir until completely dissolved and homogeneous, and add at least one of vinylene carbonate (VC), fluoroethylene carbonate (FEC), divinyl sulfite (DTD), and 1,3 - propane sultone (PST) and mix evenly to obtain the electrolyte 150. Among them, the raw material components of the electrolyte 150 in Examples 1 to 23 and Comparative Examples 1 to 4 are shown in Table 2.

[0124] 5. Preparation of the battery 100:

[0125] Stack the prepared positive electrode plate 111, separator 112, and negative electrode plate 113 in sequence. The separator 112 is disposed between the positive electrode plate 111 and the negative electrode plate 113. After winding, obtain the electrode assembly 110. Assemble the electrode assembly 110 into the accommodation cavity 141, and realize the electrical connection between the electrode assembly 110 and the end cover assembly 120 through the electrical connector 130. After drying, inject the prepared electrolyte 150 into the accommodation cavity 141, and perform encapsulation, standing, formation, shaping, capacity testing, etc. on the electrode assembly 110, and finally prepare the battery 100.

[0126] Prepare the batteries 100 of Examples 1 to 23 and Comparative Examples 1 to 4 according to the above method. Among them, the capacities of the electrode assemblies 110 of the batteries 100 in Examples 1 to 23 and Comparative Examples 1 to 4 are shown in Table 1.

[0127] Performance test of the battery 100:

[0128] 1. The positive electrode sheets 111 and the electrolytes 150 of Examples 1 to 23 and Comparative Examples 1 to 4 were assembled into coin cells, and linear sweep voltammetry tests were performed on the coin cells. The specific operations are as follows:

[0129] (1) In the battery 100, the battery 100 was 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 was 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 was in a fully charged state. Here, C represents the designed capacity of the battery 100. A current of 1C refers to the current intensity when the full capacity of the battery 100 is discharged in 1 hour. 0.5C refers to the current intensity when the full capacity of the battery 100 is discharged in 2 hours. 0.05C refers to the current intensity when the full capacity of the battery 100 is discharged within 20 hours.

[0130] (2) When the battery 100 was in the fully charged state, the battery 100 was disassembled, and the single-sided area 1113 of the positive electrode sheet 111 and the electrolyte 150 were assembled into a coin cell. The coin cell includes a working electrode, a counter electrode, and the electrolyte 150. The electrolyte 150 wets the working electrode and the counter electrode. Taking the single-sided area 1113 of the positive electrode sheet 111 as the working electrode and lithium metal as the counter electrode, a voltage was applied to the coin cell by an electrochemical workstation. The open-circuit voltage of the coin cell was 7V.

[0131] (3) At 25°C, linear sweep voltammetry tests were performed on the coin cell at a rate of 0.1 mV / s to obtain the first peak potential and the first peak current density of the coin cell.

[0132] The values of the first peak current density a1 of the coin cells 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 coin cells are shown in Table 1.

[0133] 2. The capacities of Examples 1 to 23 and Comparative Examples 1 to 4 were tested. The specific operations are as follows:

[0134] (1) The battery 100 was charged at a constant power of 0.5P to the charging cut-off voltage of the battery 100, the initial charging capacity was recorded, and the battery 100 was left standing for 10 minutes.

[0135] (2) The battery 100 is discharged at a constant power of 0.5P until the discharge cut-off voltage of a single cell of the battery 100, and the discharge capacity of the battery 100 is recorded. Herein, P refers to the rated charging or discharging power of the battery, and its value is the nominal voltage U of the battery multiplied by the current density of 1C. Among them, the nominal voltage of the lithium iron phosphate battery is 3.2V, and 0.5P refers to 0.5 times the rated power.

[0136] The capacity values of the battery 100 in Examples 1 to 23 and Comparative Examples 1 to 4 are shown in Table 1.

[0137] The performance parameters of the battery 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 plate 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 recorded in Table 1.

[0138] Table 1: Performance parameter table of the battery 100 in Examples 1 to 23 and Comparative Examples 1 to 4.

[0139]

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

[0141] Examples and Comparative Examples Raw Material Components of the Electrolyte Example 1 <![CDATA[12.5% LiPF6; EC∶DMC∶EMC = 2∶1∶1; 2% VC + 2% FEC + 1% DTD + 0.3% PST]]> Example 2 <![CDATA[12.5% LiPF6; EC∶DMC∶EMC = 2∶1∶2; 1% VC + 0.5% FEC + 2% DTD + 0.3% PST]]> Example 3 <![CDATA[12.5% LiPF6; EC∶DMC∶EMC = 2∶1∶4; 0.5% VC + 0.5% FEC + 1.5% DTD + 1% PST]]> Example 4 <![CDATA[12.5% LiPF6; EC∶DMC∶EMC = 2∶2∶1; 1% VC + 0.5% FEC + 2% DTD + 0.5% PST]]> Example 5 <![CDATA[12.5% LiPF6; EC∶DMC∶EMC = 2∶4∶1; 1% VC + 1% FEC + 2% DTD + 2% PST]]> Example 6 <![CDATA[12.5% LiPF6; EC∶DMC∶EMC = 1∶2∶2; 1% VC + 0.5% FEC + 1% DTD + 1.2% PST <!-- 17 -->]]> Example 7 <![CDATA[12.5% LiPF6; EC∶DMC∶EMC = 1∶2∶3; 1% VC + 1% FEC + 1% DTD + 1.5% PST]]> Example 8 <![CDATA[12.5% LiPF6; EC∶DMC∶EMC = 2∶3∶1; 1.5% VC + 1.5% FEC + 1% DTD + 1.5% PST]]> Example 9 <![CDATA[12.5% LiPF6; EC∶DMC∶EMC = 2∶3∶2; 2% VC + 1.5% FEC + 2% DTD + 0.5% PST]]> Example 10 <![CDATA[12.5% LiPF6; EC∶DMC∶EMC = 1∶1∶1; 4% VC + 2.5% FFC + 2% DTD + 0.5% PST]]> Example 11 <![CDATA[12.5% LipF6; EC∶DMC∶EMC = 1∶2∶2; 1% VC + 0.5% FEC + 1% DTD + 1.2% PST]]> Example 12 <![CDATA[12.5% LiPF6; EC∶DMC∶EMC = 1∶2∶2; 1% VC + 0.5% FEC + 1% DTD + 1.2% PST]]> Example 13 <![CDATA[12.5% LiPF6; EC∶DMC∶EMC = 1∶2∶2; 1% VC + 0.5% FEC + 1% DTD + 1.2% PST]]> Example 14 <![CDATA[12.5% LiPF6; EC∶DMC∶EMC = 1∶2∶2; 1% VC + 0.5% FEC + 1% DTD + 1.2% PST]]> Example 15 <![CDATA[12.5% LiPF6; EC∶DMC∶EMC = 1∶2∶2; 1% VC + 0.5% FEC + 1% DTD + 1.2% PST]]> Example 16 <![CDATA[12.5% LiPF6; EC∶DMC∶EMC = 1∶2∶2; 1% VC + 0.5% FEC + 1% DTD + 1.2% PST]]> Example 17 <![CDATA[12.5% LiPF6; EC∶DMC∶EMC = 1∶1∶1; 2% VC + 1.5% FEC + 2% DTD + 0.5% PST]]> Example 18 <![CDATA[12.5% LiPF6; EC∶DMC∶EMC = 1∶1∶1; 2% VC + 1.5% FEC + 2% DTD + 0.5% PST]]> Example 19 <![CDATA[12.5% LiPF6; EC∶DMC∶EMC = 1∶1∶1; 1% VC + 1% DTD + 1.2% PST]]> Example 20 <![CDATA[12.5% LiPF6; EC∶DMC∶EMC = 1∶2∶2; 1% VC + 0.5% FEC + 1% DTD + 1.2% PST]]> Example 21 <![CDATA[12.5% LiPF6; EC∶DMC∶EMC = 1∶2∶2; 1% VC + 0.5% FEC + 1% DTD + 1.2% PST]]> Example 22 <![CDATA[12.5% LiPF6; EC∶DMC∶EMC = 1∶1∶1; 2.5% VC + 2% DTD + 0.5% PST]]> Example 23 <![CDATA[12.5% LiPF6; EC∶DMC∶EMC = 1∶1∶1; 2.5% VC + 2% DTD + 0.5% PST]]> Comparative Example 1 <![CDATA[12.5% LiPF6; EC∶DMC∶EMC = 1∶1∶1]]> Comparative Example 2 <![CDATA[12.5% LiPF6; EC∶DMC∶EMC = 1∶1∶1]]> Comparative Example 3 <![CDATA[12.5% LiPF6; EC∶DMC∶EMC = 1∶1∶1]]> Comparative Example 4 <![CDATA[12.5% LiPF6; EC∶DMC∶EMC = 1∶1∶1]]>

[0142] Among them, 2% VC + 2% FEC + 1% DTD + 0.3% PST means 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%.

[0143] Electrochemical performance test of the battery 100:

[0144] 1. Cycle performance test:

[0145] The battery 100 is subjected to charge and discharge cycle tests on a charge and discharge instrument. The test temperature is 25 °C, the cycle rate is 1C (that is, both the charge rate and the discharge rate are 1C), and the charge voltage is from 2.5V to 3.65V. The capacity retention rate after cycling is calculated. The formula for the capacity retention rate of the battery 100 cycled at 25 °C is: Capacity retention rate after the nth cycle = (Discharge capacity after the nth cycle / Discharge capacity in the first cycle) × 100%.

[0146] For Examples 1 to 23 and Comparative Examples 1 to 4, the capacity retention rates of Battery 100 after 1000 cycles at 25°C are shown in Table 3. Among them, the capacity retention rate of Battery 100 after 1000 cycles at 25°C = (discharge capacity after the 1000th cycle / discharge capacity in the first cycle) × 100%.

[0147] 2. Overcharge safety test:

[0148] Battery 100 was tested on a charge and discharge instrument and left to stand for 5 h within the temperature range of 23°C to 27°C (such as 23°C, 25°C, 2°C, 27°C, etc.); discharged at 1C to 2.5V, charged at 1C to 3.65V and left to stand for 10 minutes. Then, Battery 100 was transferred to an overcharge test instrument for testing, and charged at a constant current of 1C until the voltage of the device reached 5.475V or the charging time reached 1 h. Observe for 1 h and record whether there are phenomena such as swelling, leakage, smoking, fire, and explosion. The overcharge performance standard for Battery 100 is as follows: If there is no leakage in Battery 100, it meets the first-level standard; if there is leakage in Battery 100 but no smoking and thermal runaway occur, it meets the second-level standard; if there is leakage, smoking, and thermal runaway in Battery 100, but there is no fire or explosion, it meets the third-level standard; if there is fire or explosion in Battery 100, it is at the fourth level, that is, it does not meet the standard;

[0149] Among them, the judgment criteria for thermal runaway are as follows: 1) The voltage of the test object is less than or equal to 1.0V; 2) The temperature monitoring sampling frequency is 1 s, and the temperature rise rate at the monitoring point is greater than or equal to 5°C / s for three consecutive times. When both situation 1) and situation 2) occur in Battery 100, it is determined that Battery 100 has experienced thermal runaway.

[0150] The overcharge performance of Batteries 100 of Examples 1 to 23 and Comparative Examples 1 to 4 is shown in Table 3.

[0151] The capacity retention rates of Batteries 100 of Examples 1 to 23 and Comparative Examples 1 to 4 measured above after 1000 cycles at 25°C and the overcharge performance of Battery 100 are shown in Table 3.

[0152] Table 3: Electrochemical performance of Batteries 100 of Examples 1 to 23 and Comparative Examples 1 to 4.

[0153]

[0154] 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, please refer to Examples 2, 4 and 5. Under the condition that 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, and the overcharge performance of the battery 100 of Examples 2, 4 and 5 is 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 5mAcm -2 , the value of a2 / a1 is greater than 30. In other words, the values of a2 and a2 / a1 are both too large, so that the amount of rigid inorganic salt compounds generated by the electrolyte 150 under overcharge is too much, and the amount of flexible organic polymer generated is too little. When the rigid inorganic salt compound combines with the flexible organic polymer to form a passivation film, the generated passivation film is too rough and not dense, which reduces 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 generated passivation film 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 moving 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 avoiding the diaphragm 112 disposed between the positive electrode plate 111 and the negative electrode plate 113 from being melted, thereby avoiding the thermal runaway of the battery 100 during the overcharging process, and finally making the capacity retention rate of the battery 100 at 25° C. for 1000 cycles higher and the overcharging performance better, that is, the cycle performance and safety performance of the battery 100 are better.

[0155] From the performance parameters and electrochemical performance parameters of the battery 100 in Example 3, Examples 6 to 10, it can be seen that on the premise that other conditions remain unchanged, as the value of the first peak current density a1 continuously increases, the value of a2 / a1 continuously decreases. On the premise that the unit reaction area c of the active material layer 1111 remains unchanged, the value of a1 / c continuously increases, causing the capacity retention rate of the battery 100 to increase first and then decrease after 1000 cycles at 25°C. The overcharge performance of the battery 100 first improves and then deteriorates. The overcharge performances of the batteries 100 in Example 3, Examples 6 to 10 are respectively three-level pass, three-level pass, two-level pass, two-level pass, three-level pass and fail. This is because in the batteries 100 of Example 3, Examples 6 to 9, the values of the first peak current density a1 of the button cell all satisfy the relationship: 0.1 mA cm -2 ≤a1≤3 mA cm -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 cells in Example 3, Examples 6 to 9 are within a reasonable range, making the thickness of the passivation film generated during the charging process of the battery 100 within a reasonable range and the value of a1 increases in sequence. The passivation film can passivate the positive electrode plate 111 and avoid the resistance of the passivation film being too thick to increase the movement resistance of the active ions 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 experience overcharge, thereby avoiding the generation of more reaction heat and Joule heat, and avoiding the diaphragm 112 disposed between the positive electrode plate 111 and the negative electrode plate 113 from being melted, thus avoiding the occurrence of thermal runaway during the overcharge process of the battery 100. Finally, the capacity retention rate and overcharge performance of the battery 100 after 1000 cycles at 25°C are gradually improved, that is, the cycle performance and safety performance of the battery 100 are improved. 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 generated by the battery 100 during charging is too large, and the degree of passivation of the electrolyte 150 on the positive electrode plate 111 is too large, so that during the continuous charging of the battery 100, the impedance of the movement of active ions in the electrolyte 150 is too large, resulting in Joule heat, increasing the heat generated by the battery 100 during overcharging, and reducing the capacity retention rate and overcharging performance of the battery 100 after 1000 cycles at 25°C, that is, reducing the cycling performance and safety performance of the battery 100. In addition, no characteristic first peak appears in the tests of the linear sweep voltammetry of the batteries 100 in Comparative Examples 1 to 4, so that when the battery 100 is in the overcharged state, the electrolyte 150 cannot form a passivation film, and thus cannot prevent the continuous reaction of the electrolyte 150 with the positive electrode plate 111, resulting in more reaction heat and Joule heat generated by the battery 100 in the overcharged state. In Comparative Examples 1 to 4, as the capacity of the battery 100 continuously increases, the heat generated by the battery 100 in the overcharged state continuously increases, and the electrolyte 150 in Comparative Examples 1 to 4 also cannot prevent the reaction of the battery 100 in the overcharged state, resulting in a continuous decrease in the capacity retention rate and overcharging performance of the battery 100 after 1000 cycles at 25°C, that is, the cycling performance and safety performance of the batteries 100 in Comparative Examples 1 to 4 decrease in turn.

[0156] Furthermore, from the performance parameters and electrochemical performance parameters of the battery 100 in Examples 6, 11 to 16, it can be seen that, on the premise that other conditions remain unchanged, as the mass fraction b of the binder in the active material layer 1111 continuously increases, the value of a1 / b also continuously increases. The capacity retention rate of the battery 100 after 1000 cycles at 25°C first increases and then decreases. The overcharge performance of the battery 100 first improves and then deteriorates. The overcharge performances of the batteries 100 in Examples 6, 11 to 16 are respectively passed at level three, passed at level three, passed at level two, passed at level two, passed at level one, passed at level two, and passed at level two. In Examples 12 to 15, the mass fraction b of the binder in the active material layer 1111 satisfies the relational expression 2% ≤ b ≤ 4%. The mass fraction of the binder is within a reasonable range. And as the mass ratio 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, thereby further reducing the reaction heat between the positive electrode plate 111 and the electrolyte 150 in the overcharged state. In addition, by setting more binders in the active material layer 1111, the reaction between the electrolyte 150 and the positive electrode plate 111 in the overcharged state can be further accelerated to be blocked, which is beneficial to shortening the reaction time of the battery 100 in the overcharged state, thereby reducing the Joule heat generated in the overcharged state and further improving the overcharge performance of the battery 100. Finally, the capacity retention rate and overcharge performance of the battery 100 after 1000 cycles at 25°C are gradually improved, that is, the cycle performance and safety performance of the battery 100 are improved. 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 there is still a large contact area between the transition metal oxide in the active material layer 1111 and the electrolyte 150. The binder is difficult to block the reaction between the positive electrode plate 111 and the electrolyte 150 in the overcharged state. The longer the reaction time of the battery 100 in the overcharged state, the more Joule heat and reaction heat are generated, resulting in poorer capacity retention rate and overcharge performance of the battery 100 in Example 6 and the battery 100 in Example 11 compared with the batteries 100 in Examples 12 to 15 after 1000 cycles at 25°C. Furthermore, the mass fraction b of the binder in the battery 100 in Example 16 is greater than 4%, increasing the impedance of the active material layer 1111, 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 overcharged state, and reducing the cycle performance and overcharge performance of the battery 100.In Comparative Examples 1 to 4, no binder was provided in the active material layer 1111 of the battery 100, and the reaction time of the battery 100 in the overcharged state could not be further shortened, resulting in poor cycling performance and overcharge performance of the batteries 100 in Comparative Examples 1 to 4.

[0157] Furthermore, from the performance parameters and electrochemical performance parameters of the batteries 100 in 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 batteries 100 in Examples 18, 20, and 21 all satisfy the range 0.1623m 2 ·cm -2 ≤c≤0.416m 2 ·cm -2 ,the values of a1 / b all satisfy the range 0.025mAcm -2 ≤a1 / b≤1mAcm -2 ,and the values of a1 / c all satisfy the range 0.24mAm -2 ≤a1 / c≤12.32mAm -2, such 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 passes the first level. 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 relatively large, the mass proportion of the binder in the active material layer 1111 is relatively high, which reduces the contact area between the transition metal oxide in the active material layer 1111 and the electrolyte 150, and then further reduces the reaction heat between the positive electrode sheet 111 and the electrolyte 150 in the overcharged state. In addition, if the value of a1 / c is relatively large, the first peak current density is relatively large, which is beneficial to improving the passivation degree of the electrolyte 150 in the overcharged state, so that the batteries of Example 17 and Example 18 both have a high capacity retention rate. From the data of Example 19 to Example 21, it can be seen that as the unit reaction area c of the active material layer 1111 continuously increases, the capacity retention rate of the battery 100 after 1000 cycles at 25 °C decreases. This is because when the battery 100 is in the 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, resulting in more reaction heat generated between the active material layer 1111 and the electrolyte 150 in the overcharged state, increasing the risks of thermal runaway, fire or explosion of the battery 100 in the overcharged state, thereby reducing the capacity retention rate of the battery 100. From the data of Example 22 and Example 23, it can be seen that when the mass proportion of the binder is too low, 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 sheet 111. The positive electrode sheet 111 can still react with the electrolyte 150 to generate more reaction heat, and the lower the capacity retention rate of the battery 100 after 1000 cycles at 25 °C, and the worse the cycling performance of the battery 100.

[0158] In summary, when the battery 100 satisfies one or more of the following conditions, the battery 100 has good cycling performance and overcharge performance. Among them, the value of the first peak current density a1 satisfies the range 0.1 mAcm -2 ≤a1≤3 mAcm -2 , the second peak current density a2 of the coin cell satisfies: 0.3 mAcm -2 ≤a2≤5 mAcm -2 , the ratio of the second peak current density to the first peak current density of the coin cell satisfies: 0.1 ≤ a2 / a1 ≤ 30, the mass fraction b of the binder in the active material layer 1111 satisfies the range 2% ≤ b ≤ 4%, and the value of a1 / b satisfies the range 0.025 mAcm -2≤a1 / b≤1 mA / cm -2 and the value of a1 / c satisfies the range of 0.24 mA / m -2 ≤a1 / c≤12.32 mA / m -2 When this is the case, the battery 100 has a high capacity retention rate and good overcharge performance after 1000 cycles at 25 °C, that is, the battery 100 has good cycling performance and overcharge performance.

[0159] 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 only examples of the electrolyte 150 in each embodiment, and should not be construed as a limitation on the raw material components of the electrolyte 150.

[0160] Please refer to Figure 8 , the embodiments of the present application further provide an energy storage device 200, and the energy storage device 200 includes a plurality of batteries 100 provided by the present application, and the plurality of batteries 100 are electrically connected to each other.

[0161] In the embodiments of the present application, the plurality of batteries 100 are electrically connected in series, parallel or in a hybrid connection. The battery 100 can reduce heat generation, and the battery 100 has excellent cycling performance and overcharge performance. The plurality of batteries 100 are arranged in the energy storage device 200, which is beneficial to improving the cycling performance of the energy storage device 200, reducing the reaction heat or Joule heat generated by the energy storage device 200 in the overcharged state, and avoiding the phenomenon that the energy storage device 200 undergoes thermal runaway, fire or explosion due to excessive heat, thereby improving the cycling performance and safety performance of the energy storage device 200.

[0162] Optionally, the energy storage device 200 includes a box body 210, and the box body 210 encloses an accommodation cavity 211 for accommodating the plurality of batteries 100.

[0163] Please refer to Figure 9 and Figure 10 , the embodiments of the present application further provide an electrical equipment 300, and the electrical equipment 300 includes: an equipment body 310 and the energy storage device 200 provided by the present application, and the energy storage device 200 supplies power to the equipment body 310. In other words, the energy storage device 200 is electrically connected to the equipment body 310.

[0164] In this embodiment, the energy storage device 200 has both high cycling performance and safety performance, so that the energy storage device 200 can provide a stable power supply for the equipment body 310, enabling the equipment body 310 to work stably.

[0165] The electrical device 300 according to the embodiments of the present application may be, but is not limited to, portable electronic devices such as mobile phones, tablet computers, laptop computers, desktop computers, smart bracelets, smart watches, e-readers, game consoles, etc. It may also be transportation means such as cars, trucks, sedans, freight trucks, bullet trains, high-speed rails, electric scooters, etc. In addition, it may also be various household appliances, etc.

[0166] It can be understood that the electrical device 300 described in this embodiment is only one form of the electrical device 300 to which the energy storage device 200 is applied, and should not be construed as a limitation on the electrical device 300 provided in the present application, nor should it be construed as a limitation on the electrical device 300 provided in each embodiment of the present application. In the present application Figure 9 In the embodiment, the electrical device 300 is an energy storage battery cabinet.

[0167] The mention of "embodiment" and "embodiment mode" in the present application means that the specific features, structures or characteristics described in connection with the embodiment may be included in at least one embodiment of the present application. The appearance of the phrase at various positions in the specification does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment mutually exclusive with other embodiments. Those skilled in the art explicitly and implicitly understand that the embodiments described in the present application may be combined with other embodiments. In addition, it should also be understood that the features, structures or characteristics described in each embodiment of the present application can be combined arbitrarily without contradiction to form another embodiment that does not deviate from the spirit and scope of the technical solution of the present application.

[0168] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present application and not to limit them. Although the present application has been described in detail with reference to the above preferred embodiments, those of ordinary skill in the art should understand that the technical solutions of the present application can be modified or equivalently replaced without departing from the spirit and scope of the technical solutions of the present application.

Claims

1. A battery, characterized in that, The battery includes: An electrode assembly, which includes a positive electrode tab, a separator, and a negative electrode tab stacked in sequence; the positive electrode tab includes an active material layer and a current collector layer, the active material layer is disposed on the outer 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 relation: 2% ≤ b ≤ 4%; the active material layer further includes an active material, and the active material is lithium iron phosphate; and An electrolyte, which at least wets part of the electrode assembly, and the electrolyte includes a lithium salt, and the lithium salt is lithium hexafluorophosphate; Among them, the battery in the fully charged state is disassembled to obtain the positive electrode sheet. The positive electrode sheet and the electrolyte are assembled into a coin cell, and linear sweep voltammetry testing is performed on the coin cell at a potential sweep rate of 0.1 mV / s. The first peak current density a1 of the coin cell satisfies the relationship: 0.1 mAcm -2 ≤ a1 ≤ 3 mAcm -2 ; The ratio of the first peak current density a1 of the button cell to the mass fraction b of the binder satisfies the relation: 0.025 ≤ a1 / b ≤ 1; 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 relation: 0.24 mA / m -2 ≤ a1 / c ≤ 12.32 mA / m -2 , where 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.

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

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

4. The battery according to claim 3, characterized in that, The second peak current density a2 of the button cell satisfies: 0.3 mA / cm -2 ≤ a2 ≤ 5 mA / cm -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 cell satisfies: 0.1 ≤ a2 / a1 ≤ 30.

6. The battery according to any one of claims 1 to 5, characterized in that, The electrolyte further includes a film-forming additive, and in the electrolyte, the mass fraction g of the film-forming additive satisfies the relation: 2% ≤ g ≤ 10%.

7. The battery according to claim 6, characterized in that, The film-forming additive includes at least one of vinylene carbonate, fluoroethylene carbonate, ethylene sulfate, and 1,3-propane sultone.

8. The battery according to claim 1, characterized in that, The unit reaction area c of the active material layer satisfies the relationship: 0.1623 m 2 ·cm -2 ≤ c ≤ 0.416 m 2 ·cm -2 .

9. The battery according to claim 1, wherein The current collector layer includes aluminum.

10. The battery according to claim 1, characterized in that, The binder is polyvinylidene fluoride.

11. A method for selecting an electrolyte, characterized in that, The method for selecting the electrolyte includes: Providing a test battery, which includes a positive electrode tab and an electrolyte, the positive electrode tab includes an active material layer and a current collector layer, the active material layer is disposed on the outer 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 relation: 2% ≤ b ≤ 4%; the active material layer further includes an active material, and the active material is lithium iron phosphate; the electrolyte includes a solvent, a lithium salt, and an additive, the solvent includes at least one of ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate, the lithium salt is lithium hexafluorophosphate, and the additive includes at least one of vinylene carbonate, fluoroethylene carbonate, ethylene sulfate, and 1,3-propane sultone; charging the test battery to make the test battery in a fully charged state; Disassembling the test battery to obtain the positive electrode tab, using the positive electrode tab as a working electrode, using lithium metal as a counter electrode, and assembling the positive electrode tab, lithium metal, and the electrolyte into a button cell; Performing a linear sweep voltammetry test on the button cell to obtain the first peak potential P1 and the first peak current density a1 of the button cell; and When the first peak potential P1 satisfies the relationship: 4.65 V ≤ P1 ≤ 4.9 V, the first peak current density a1 satisfies the relationship: 0.1 mA / cm² -2 ≤ a1 ≤ 3 mA / cm² -2 The ratio of the first peak current density a1 to the mass fraction b of the binder satisfies the relationship: 0.025 ≤ a1 / b ≤ 1, and the ratio of the first peak current density a1 to the unit reaction area c of the active material layer satisfies the relationship: 0.24 mA / m² -2 ≤ a1 / c ≤ 12.32 mA / m² -2 for the electrolyte, where 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.

12. The method for selecting an electrolyte according to claim 11, wherein The method for selecting the electrolyte further includes: Obtain the second peak potential P2 and the second peak current density a2 of the button cell; when the second peak potential P2 satisfies the relational expression: 3.3 V ≤ P2 ≤ 4.0 V, the second peak current density a2 satisfies the relational expression: 0.3 mA / cm -2 ≤ a2 ≤ 5 mA / cm -2 of the electrolyte solution.

13. The method for selecting an electrolyte according to claim 11, wherein The performing a linear sweep voltammetry test on the button cell to obtain the first peak potential P1 and the 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 0.1mV / s.

14. An energy storage device, characterized in that, The energy storage device includes a plurality of batteries as described in any one of claims 1-10, and the plurality of batteries are electrically connected to each other.

15. An electrical device, characterized in that, The electrical equipment includes: An equipment body; and The energy storage device as described in claim 14, and the energy storage device supplies power to the equipment body.

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