WO2024012166A1 - Rechargeable battery and electric apparatus - Google Patents

Abstract

The present application relates to a rechargeable battery and an electric apparatus. The rechargeable battery comprises a negative electrode plate, which comprises a negative current collector, a first negative active coating, and a second negative active coating, wherein the first negative active coating is arranged on at least one surface of the negative current collector, the second negative active coating is arranged between the first negative active coating and the negative current collector, the impedance of the first negative active coating is less than the impedance of the second negative active coating, and the capacity of the first negative active coating is denoted as C₁. The rechargeable battery is subjected to rapid heating charging at a charging rate of 0.3-5 C from an initial temperature T₀ until the temperature is increased by ΔT, and the capacity of the rechargeable battery is denoted as C₀ when the rapid heating charging ends; T₀ ranges from -20°C to 0°C, and ΔT ≥ 5℃; and the rechargeable battery satisfies C₁ ≥ C₀.

Description

Secondary batteries and electrical devices

This application claims priority to the Chinese patent application filed with the China Patent Office on July 11, 2022, with the application number 2022108092862 and the invention name "Second Battery and Electric Device", the entire content of which is incorporated into this application by reference. .

Technical field

The present invention relates to the field of battery technology, and in particular to a secondary battery and an electrical device.

Background technique

Secondary batteries are widely used in various consumer electronics and electric vehicles due to their outstanding characteristics such as light weight, no pollution, and no memory effect.

Taking lithium-ion batteries as an example, secondary batteries generally have problems such as increased battery internal resistance, reduced discharge performance, and significantly reduced capacity retention at low temperatures, especially when the temperature is below 0°C. In order to improve the low-temperature performance of secondary batteries, there are currently mainly the following technical means. One method is to improve low-temperature performance by increasing the ambient temperature, such as adding a heating module to the secondary battery. However, this will increase the size of the secondary battery. Another method is to improve the low-temperature charging method of batteries. However, this method is difficult to balance the safety performance and energy density of secondary batteries in low-temperature environments.

Contents of the invention

Based on this, it is necessary to provide a secondary battery and an electrical device.

A first aspect of the present application provides a secondary battery, including a negative electrode sheet. The negative electrode sheet includes a negative electrode current collector, a first negative electrode active coating, and a second negative electrode active coating. The first negative electrode active coating Disposed on at least one surface of the negative electrode current collector, the second negative electrode active coating is provided between the first negative electrode active coating and the negative electrode current collector, and the impedance of the first negative electrode active coating Less than the impedance of the second negative active coating, the capacity of the first negative active coating Denoted as C ₁ ;

The secondary battery is rapidly thermally charged from the initial temperature T ₀ at a charging rate of 0.3C to 5C until the temperature rises ΔT. The capacity of the secondary battery at the end of the rapid thermal charging is recorded as C ₀ ; T ₀ is - 20℃～0℃, ΔT≥5℃;

The secondary battery satisfies: C ₁ ≥ _{C 0} .

In any embodiment of the present application, the secondary battery satisfies: 2C ₀ ≥ C ₁ ≥ _{C 0} .

In any embodiment of the present application, 1.5C ₀ ≥ C ₁ ≥ _{C 0} .

In any embodiment of the present application, the temperature of the secondary battery is increased by ΔT to the target temperature T ₁ , and T ₁ is -5°C to 15°C.

In any embodiment of the present application, T ₁ is -10°C to 5°C.

In any embodiment of the present application, T ₀ is -20°C to -10°C.

In any embodiment of the present application, ΔT≥10°C.

In any embodiment of the present application, the first negative active coating includes a first negative active material, and the total mass of the first negative active material is recorded as m ₁ in g; The gram capacity is recorded as a, and the unit is A·h/g;

Then m ₁ =C ₁ /a.

In any embodiment of the present application, the total capacity of the secondary battery is recorded as C _Z , and the unit is A·h;

C ₁ /C _Z =30% to 60%, optionally, C ₁ /C _Z = 30% to 40%.

In any embodiment of the present application, the capacity of the second negative active coating is recorded as C ₂ , and the unit is A·h;

The second negative active coating includes a second negative active material. The total mass of the second negative active material is m ₂ in g. The gram capacity of the second negative active material is b in unit. A·h/g;

Then C ₂ =C _Z -C ₁ ; m ₂ =C ₂ /b.

In any embodiment of the present application, the first negative active material is selected from natural graphite, soft At least one of carbon, hard carbon and coated graphite, the coating layer of the coated graphite contains at least one of soft carbon and hard carbon, the second negative active material is selected from artificial graphite.

In any embodiment of the present application, the average volume particle diameter Dv50 of the first negative active material is smaller than the average volume particle diameter Dv50 of the second negative active material.

In any embodiment of the present application, the average volume particle size Dv50 of the first negative active material is 3 to 12 μm, optionally 6 to 12 μm.

In any embodiment of the present application, the average volume particle size Dv50 of the second negative active material is 9 to 17 μm.

In any embodiment of the present application, the porosity of the first negative active coating is greater than the porosity of the second negative active coating.

In any embodiment of the present application, the porosity of the first negative active coating is 25% to 40%.

In any embodiment of the present application, the porosity of the second negative active coating is 20% to 30%.

In any embodiment of the present application, the charging method of the secondary battery at temperature T ₀ includes the following steps S10-S20:

Step S10: The secondary battery is charged rapidly from the initial temperature T ₀ at a charging rate of 0.3C to 5C until the temperature rises ΔT, so that the temperature reaches the target temperature T ₁ ;

Step S20: The secondary battery continues to be charged from the target temperature T ₁ to 80% SOC to 100% SOC at a charging rate of 0.5C to 5C.

In any embodiment of the present application, the unit of C ₁ is A·h;

The theoretical heat required for the rapid thermal charging is recorded as Q ₁ , and the unit of Q ₁ is J;

The polarization voltage of the secondary battery in the rapid thermal charging is U _J , and the balance voltage of the secondary battery is _UP ; the units of U _J and _UP are V; the rapid thermal charging charges The capacity of the above-mentioned secondary battery is recorded as C ₀ ';

C ₀ '=Q ₁ /(3600U _J -3600U _P ).

In any embodiment of the present application, the mass of the secondary battery is denoted as m, and the average specific heat capacity of the secondary battery is denoted as C, then Q ₁ =m*C*ΔT.

A second aspect of the present application provides an electrical device, including the secondary battery of the first aspect of the present application.

The negative electrode plate of the secondary battery of the present application is provided with a first negative electrode active coating and a second negative electrode active coating with different impedances, and the first negative electrode active coating with smaller impedance is arranged between the second negative electrode active coating. above, and further control the capacity C ₁ of the first negative electrode active coating to be greater than or equal to the capacity C ₀ of the secondary battery at the end of rapid thermal charging at the low ambient temperature T ₀ through the above-mentioned specific large charging rate, so that the first The negative active coating meets the capacity requirements of rapid thermal charging and increases the temperature of the secondary battery by ΔT from the lower initial temperature T ₀ , thus improving the low-temperature lithium evolution window, thus reducing the lithium evolution problem under traditional low-temperature charging and improving safety. performance; at the same time, the second negative electrode active coating meets the overall energy density demand of the secondary battery in a low-temperature environment. In this way, the above-mentioned secondary battery can take into account both safety performance and energy density in low-temperature environments.

Description of drawings

FIG. 1 is a schematic diagram of a secondary battery according to an embodiment of the present application.

Figure 2 is a schematic cross-sectional structural view of the negative electrode tab in the secondary battery according to an embodiment of the present application shown in Figure 1;

FIG. 3 is an exploded view of the secondary battery according to the embodiment of the present application shown in FIG. 1 .

Figure 4 is a schematic diagram of a battery module according to an embodiment of the present application.

Figure 5 is a schematic diagram of a battery pack according to an embodiment of the present application.

FIG. 6 is an exploded view of the battery pack according to an embodiment of the present application shown in FIG. 5 .

FIG. 7 is a schematic diagram of a power consumption device using a secondary battery as a power source according to an embodiment of the present application.

Explanation of reference symbols:
1 battery pack; 2 upper box; 3 lower box; 4 battery module; 5 secondary battery; 51 shell;
52 electrode assembly; 53 cover plate; 6 electrical device; 7 negative electrode piece; 71 first negative active material; 72 second negative electrode active material; 73 negative electrode current collector.

Detailed ways

Hereinafter, embodiments in which the secondary battery and the power consumption device of the present application are specifically disclosed will be described in detail with reference to the drawings as appropriate. However, unnecessary detailed explanations may be omitted. For example, detailed descriptions of well-known matters may be omitted, or descriptions of substantially the same structure may be repeated. This is to prevent the following description from becoming unnecessarily lengthy and to facilitate understanding by those skilled in the art. In addition, the drawings and the following description are provided for those skilled in the art to fully understand the present application, and are not intended to limit the subject matter described in the claims.

"Ranges" disclosed herein are defined in terms of lower and upper limits. A given range is defined by selecting a lower limit and an upper limit that define the boundaries of the particular range. Ranges defined in this manner may be inclusive or exclusive of the endpoints, and may be arbitrarily combined, that is, any lower limit may be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a particular parameter, understand that ranges of 60-110 and 80-120 are also expected. Furthermore, if the minimum range values 1 and 2 are listed, and if the maximum range values 3, 4, and 5 are listed, then the following ranges are all expected: 1-3, 1-4, 1-5, 2- 3, 2-4 and 2-5. In this application, unless stated otherwise, the numerical range "a-b" represents an abbreviated representation of any combination of real numbers between a and b, where a and b are both real numbers. For example, the numerical range "0-5" means that all real numbers between "0-5" have been listed in this article, and "0-5" is just an abbreviation of these numerical combinations. In addition, when stating that a certain parameter is an integer ≥ 2, it is equivalent to disclosing that the parameter is an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

If there is no special description, all embodiments and optional embodiments of the present application can be combined with each other to form new technical solutions.

If there is no special description, all technical features and optional technical features of the present application can be combined with each other to form new technical solutions.

If there is no special instructions, all steps of this application can be performed sequentially or randomly. Carry out, preferably sequentially. For example, the method includes steps (a) and (b), which means that the method may include steps (a) and (b) performed sequentially, or may include steps (b) and (a) performed sequentially. For example, mentioning that the method may also include step (c) means that step (c) may be added to the method in any order. For example, the method may include steps (a), (b) and (c). , may also include steps (a), (c) and (b), may also include steps (c), (a) and (b), etc.

If there is no special explanation, the words "include" and "include" mentioned in this application represent open expressions, which may also be closed expressions. For example, "comprising" and "comprising" may mean that other components not listed may also be included or included, or only the listed components may be included or included.

In this application, the term "or" is inclusive unless otherwise specified. For example, the phrase "A or B" means "A, B, or both A and B." More specifically, condition "A or B" is satisfied by any of the following conditions: A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists) ; Or both A and B are true (or exist).

In one embodiment of the present application, a secondary battery is provided.

Typically, a secondary battery includes a positive electrode plate, a negative electrode plate, an electrolyte and a separator. During the charging and discharging process of the battery, active ions are inserted and detached back and forth between the positive and negative electrodes. The electrolyte plays a role in conducting ions between the positive and negative electrodes. The isolation film is placed between the positive electrode piece and the negative electrode piece. It mainly prevents the positive and negative electrodes from short-circuiting and allows ions to pass through.

FIG. 1 shows a square-structured secondary battery 5 as an example.

Negative pole piece

The negative electrode sheet includes a negative electrode current collector, a first negative electrode active coating and a second negative electrode active coating. The first negative active coating is disposed on at least one surface of the negative current collector, and the second negative active coating is disposed between the first negative active coating and the negative current collector. In other words, the first negative electrode active coating layer is disposed on the surface of the second negative electrode active coating layer away from the negative electrode current collector.

The resistance of the first negative active coating is less than the resistance of the second negative active coating, and the capacity of the first negative active coating is recorded as C ₁ .

The secondary battery is rapidly charged from the initial temperature T ₀ at a charging rate of 0.3C to 5C until the temperature rises ΔT. The capacity of the secondary battery at the end of the rapid thermal charge is recorded as C ₀ ; T ₀ is -20°C to 0°C. ΔT≥5℃;

The secondary battery satisfies: C ₁ ≥ _{C 0} .

It should be noted that in an environment where T ₀ is -20°C ~ 0°C, the general charging rate is 0.02C and below; in this application, in an environment where T ₀ is -20°C ~ 0°C, the charging rate is controlled at 0.3 C~5C is a relatively large charging rate.

It can be understood that the capacity of the secondary battery charged by rapid thermal charging is recorded as C ₀ ', and the capacity of the secondary battery at the beginning of rapid thermal charging is C _Q , then C ₀ =C ₀ '+C _Q .

Without wishing to be limited to any theory, the negative electrode plate of the secondary battery of the present application is provided with a first negative electrode active coating and a second negative electrode active coating with different impedances, and the first negative electrode active coating with smaller impedance is arranged on the third negative electrode active coating. above the two negative electrode active coatings, and further controls the capacity C ₁ of the first negative electrode active coating to be greater than or equal to the capacity C of the secondary battery at the end of rapid thermal charging at the low temperature ambient temperature T ₀ through the above-mentioned specific large charging rate. ₀ , thus enabling the first negative electrode active coating to meet the capacity requirements of rapid thermal charging, and increasing the temperature of the secondary battery by ΔT from the lower initial temperature T ₀ , thereby improving the low-temperature lithium evolution window, thereby reducing the risk of lithium evolution under traditional low-temperature charging. It eliminates the problem of lithium precipitation and improves safety performance; at the same time, the second negative electrode active coating is used to meet the overall energy density demand of secondary batteries in low-temperature environments. In this way, the above-mentioned secondary battery can take into account both safety performance and energy density in low-temperature environments.

It can be understood that the negative electrode current collector has two opposite surfaces in its own thickness direction, and the second negative electrode active coating is disposed on any one or both of the two opposite surfaces of the negative electrode current collector. For example, in some examples, the second negative electrode active coating layer may be provided on two opposite surfaces of the negative electrode current collector; the first negative electrode active material may also be provided on the two second negative electrode active coating layers on both surfaces thereof. As shown in FIG. 2 , the negative electrode sheet 7 includes a negative electrode current collector 73 , a first negative electrode active coating 71 and a second negative electrode active coating 72 . The first negative active coating 71 is provided on a surface of the negative current collector 73 , and the second negative active coating 72 is provided between the first negative active coating 71 and the negative current collector 73 .

In some embodiments, the secondary battery satisfies: 2C ₀ ≥ C ₁ ≥ _{C 0} . In some examples, C ₁ can be C ₀ , 1.3C ₀ , 1.5C ₀ , 2C ₀ . Further, 1.5C ₀ ≥C ₁ ≥C ₀ ; further, 1.3C ₀ ≥C ₁ ≥C ₀ .

It is understood that T ₀ can be -20°C, -15°C, -10°C, -5°C, -2°C, or 0°C. Further, T ₀ is -20°C to -10°C. It can be understood that ΔT can be 5°C, 6°C, 8°C, 10°C, 15°C, 18°C, 20°C, 23°C, or 25°C. In some embodiments, ΔT≥10°C; further, 35°C≥ΔT≥10°C.

In some embodiments, the temperature of the secondary battery is increased by ΔT to the target temperature T ₁ , where T ₁ is -10°C to 15°C. Optionally, T ₁ is -10°C to 5°C. Further optionally, T ₁ is -5°C to 5°C. The target temperature can reach the normal charging rate requirement within this temperature range.

In some embodiments, the above-mentioned charging method of the secondary battery at temperature T ₀ includes the following steps S10-S20:

Step S10: The secondary battery is rapidly charged from the initial temperature T ₀ at a charging rate of 0.3C to 5C until the temperature rises ΔT, so that the temperature reaches the target temperature T ₁ ; T ₀ is -20°C to 0°C, ΔT≥5 ℃. The charging rate of 0.3C to 5C at the initial temperature T ₀ is a relatively large charging rate.

Step S20: The secondary battery continues to be charged from the target temperature _T1 to 80% SOC to 100% SOC (fully charged) at a charging rate of 0.5C to 5C. When the temperature rises to the target temperature T ₁ , the charging window is relaxed, and the charging rate of 0.5C to 5C is a relatively conventional charging rate.

It can be understood that the charging rate in step S20 can be 0.5C, 1C, 1.5C, 1.7C, 2.9C, 3C, 4C, 5C; further, the charging rate in step S20 is 0.5C˜3C.

The above-mentioned secondary battery is subjected to high-rate rapid thermal charging at low temperature through step S10. The time required for rapid thermal charging is short. At the same time, the charging curve of the secondary battery during rapid thermal charging is deviated from the equilibrium potential as much as possible to generate as much energy as possible. More polarization heat is used to increase the temperature rise of the battery core, thereby improving the low-temperature lithium evolution window. However, you cannot use high-rate continuous charging to 80% SOC ~ 100% SOC, because the battery charging window is narrow at this time. If you continue to use high-rate rapid thermal charging strategy to charge to 80% SOC ~ 100% SOC, the secondary battery will be easily analyzed. Lithium, causing safety accidents. Therefore, step S20 uses the normal charging rate to charge when the target temperature T ₁ is reached to ensure safety.

The above-mentioned secondary battery of the present application adopts the above-mentioned charging method and at the same time optimizes the negative electrode plate to match Equipped with this charging method, the above-mentioned secondary battery can take into account both safety performance and energy density in low-temperature environments.

In some embodiments, the unit of C ₁ is A·h; the theoretical heat required for rapid thermal charging is denoted as Q ₁ , and the unit of Q ₁ is J. The mass of the secondary battery is denoted by m, and the average specific heat capacity of the secondary battery is denoted by C, then Q ₁ =m*C*ΔT.

The polarization voltage of the secondary battery during rapid thermal charging is U _J , and the equilibrium voltage of the secondary battery is _UP ; the units of U _J and _UP are V; in this way, the first negative active material of the secondary battery during rapid thermal charging The polarization heat generated during the process Q ₂ =(U _{J -UP} )*C ₀ '*3600. As mentioned above, C ₀ ′ refers to the capacity of the secondary battery charged by rapid thermal charging, which is essentially the capacity of the first negative electrode active material. According to Q ₁ = Q ₂ , then there is:

C ₀ '=Q ₁ /(3600U _J -3600U _P )=m*C*ΔT/(3600U _J -3600U _P ).

Among them, the mass m of the secondary battery refers to the total mass including the outer packaging, top cover and bare cells. The average specific heat capacity of a secondary battery is the energy required for every 1°C increase in temperature of the secondary battery as a whole. The average specific heat capacity C of the secondary battery can be tested by the following method: charge and discharge the secondary battery in an accelerated adiabatic calorimeter (ARC) or homemade adiabatic equipment, and record the voltage, temperature, charge and discharge time and other data of the secondary battery. , and then based on the battery thermal theoretical model proposed by Newman et al., the calorific value Q ₂ of the secondary battery was theoretically calculated, and finally the average specific heat capacity C of a single secondary battery was back calculated through the formula Q ₂ =C m△T. Then Q 1 can be obtained through Q ₁ =m*C*ΔT; and C _{0 '} can be obtained according to C ₀ '= Q ₁ / (3600U _J -3600U _P ).

Rapid thermal charging is a polarization process of high-rate charging, and U _J refers to the average voltage during the rapid thermal charging stage.

U _P refers to the voltage charged at 0.05C at 25°C. At this time, the charging rate is small enough and there is no polarization voltage, so it is a balanced voltage.

In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. For example, as the metal foil, copper foil can be used. The composite current collector may include a polymer material base layer and a metal layer formed on at least one surface of the polymer material base material. The composite current collector can be The metal material is formed on the polymer material substrate.

Among them, metal materials include but are not limited to copper, copper alloys, nickel, nickel alloys, titanium, titanium alloys, silver and silver alloys, etc. Polymer material substrates include but are not limited to polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE).

In some embodiments, the first negative active coating includes a first negative active material. The second negative active coating includes a second negative active material. The first negative electrode active material and the second negative electrode active material may adopt negative electrode active materials known in the art for use in batteries.

In some embodiments, the first negative active coating and the second negative active coating optionally further include a binder. The binder can be selected from styrene-butadiene rubber (SBR), polyacrylic acid (PAA), polysodium acrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), poly At least one of methacrylic acid (PMAA) and carboxymethyl chitosan (CMCS).

In some embodiments, the first negative active coating and the second negative active coating optionally further include a conductive agent. The conductive agent may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene and carbon nanofibers.

In some embodiments, the first negative active coating and the second negative active coating optionally include other auxiliaries, such as thickeners (such as sodium carboxymethylcellulose (CMC-Na)) and the like.

In some embodiments, the negative electrode sheet can be prepared by using the above-mentioned components for preparing the negative electrode sheet, such as the first negative active material or the second negative active material, the conductive agent, the binder, and any other components. The particles are dispersed in a solvent (such as deionized water) to form a first negative electrode slurry and a second negative electrode slurry respectively; the second negative electrode slurry and the first negative electrode slurry are coated on the negative electrode current collector, dried, After cold pressing and other processes, the negative electrode piece can be obtained.

The total mass of the first negative active material in the first negative active coating is recorded as m ₁ in g; the gram capacity of the first negative active material is recorded as a in A·h/g. According to the capacity C ₁ of the first negative active coating and the gram capacity a of the first negative active material, m ₁ =C ₁ /a.

Further, based on the total mass m ₁ of the first negative active material in the first negative active coating and the mass content of the first negative active material in the first negative slurry, the coating quality of the first negative slurry can be obtained. That is: the coating mass of the first negative electrode slurry = the total mass m ₁ of the first negative electrode active material in the first negative electrode active coating layer / the mass content of the first negative electrode active material in the first negative electrode slurry.

In some embodiments, the total capacity of the secondary battery is denoted C _Z , and the unit is A·h. Further, C ₁ /C _Z =30% to 60%, such as 30%, 40%, 50%, and 60%. Furthermore, C ₁ /C _Z =30% to 40%.

The capacity of the second negative active coating is recorded as C ₂ , and the unit is A·h.

The total mass of the second negative active material in the second negative active coating is recorded as m ₂ in g; the gram capacity of the second negative active material is recorded as b in A·h/g. According to the total capacity C _Z of the secondary battery and the capacity C ₁ of the first negative electrode active coating, C ₂ =C _Z -C ₁ .

According to the capacity C ₂ of the second negative active coating and the gram capacity b of the second negative active material, m ₂ =C ₂ /b.

Further, based on the total mass m ₂ of the second negative electrode active material in the second negative electrode active coating and the mass content of the second negative electrode active material in the second negative electrode slurry, the coating quality of the second negative electrode slurry can be obtained. That is: the coating mass of the second negative electrode slurry = the total mass m ₂ of the second negative electrode active material in the second negative electrode active coating / the mass content of the second negative electrode active material in the second negative electrode slurry.

In some embodiments, the first negative active material is selected from at least one of natural graphite, soft carbon, hard carbon and coated graphite, and the coating layer of the coated graphite contains at least one of soft carbon and hard carbon. A sort of. In some of these embodiments, the second negative active material is selected from artificial graphite.

In this way, by using a specific type of first negative active material, its resistance is relatively small, so the resistance of the first negative active coating is small; by using a specific type of second negative active material, its resistance is relatively large, Therefore, the resistance of the second negative active coating layer is relatively large, so that the first negative active coating layer can better meet the capacity requirements of rapid thermal charging. In addition, the cost of the secondary battery can also be reduced by matching specific types of the first negative active material and the second negative active material.

In some embodiments, the average volume particle diameter Dv50 of the first negative active material is smaller than the average volume particle diameter Dv50 of the second negative active material. In this way, by defining the relative sizes of the average volume particle diameters of the first and second negative electrode active materials, so that the resistance of the first negative electrode active coating is smaller than the resistance of the second negative electrode active coating, the first negative electrode active coating can be layer to better meet the capacity needs of fast thermal charging.

Among them, Dv50 refers to the particle size corresponding to when the cumulative particle size distribution number of particles reaches 50% in the particle size distribution curve. Its physical meaning is that 50% of the particles have a particle size smaller (or larger) than it. As an example, Dv50 can be easily measured using a laser particle size analyzer, such as the Mastersizer 2000E laser particle size analyzer of Malvern Instruments Co., Ltd. in the United Kingdom, referring to the GB/T 19077-2016 particle size distribution laser diffraction method.

Further, the average volume particle diameter Dv50 of the first negative active material is 3 to 12 μm; optionally, it is 6 to 12 μm.

Further, the average volume particle diameter Dv50 of the second negative electrode active material is 9 to 17 μm.

In some embodiments, the porosity of the first negative active coating is greater than the porosity of the second negative active coating. In this way, by defining the relative sizes of the porosity of the first and second negative electrode active materials, the first negative electrode active coating can better meet the capacity requirements of rapid thermal charging.

Further, the porosity of the first negative active coating layer is 25% to 40%.

Further, the porosity of the second negative active coating layer is 20% to 30%.

Positive electrode piece

The positive electrode sheet includes a positive electrode current collector and a positive electrode film layer disposed on at least one surface of the positive electrode current collector. The positive electrode film layer includes a positive electrode active material.

As an example, the positive electrode current collector has two surfaces facing each other in its own thickness direction, and the positive electrode film layer is disposed on any one or both of the two opposite surfaces of the positive electrode current collector.

In some embodiments, the positive electrode current collector may be a metal foil or a composite current collector. For example, as the metal foil, aluminum foil can be used. The composite current collector may include a polymer material base layer and a metal layer formed on at least one surface of the polymer material base layer. Composite current collectors can be made by adding gold The metal material is formed on the polymer material substrate. Among them, metal materials include but are not limited to aluminum, aluminum alloys, nickel, nickel alloys, titanium, titanium alloys, silver and silver alloys, etc. Polymer material substrates include but are not limited to polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE) at least one.

In some embodiments, the cathode active material may be a cathode active material known in the art for batteries. As an example, the cathode active material may include at least one of the following materials: an olivine-structured lithium-containing phosphate, a lithium transition metal oxide, and their respective modified compounds. However, the present application is not limited to these materials, and other traditional materials that can be used as positive electrode active materials of batteries can also be used. Only one type of these positive electrode active materials may be used alone, or two or more types may be used in combination. Examples of lithium transition metal oxides may include, but are not limited to, lithium cobalt oxides (such as LiCoO ₂ ), lithium nickel oxides (such as LiNiO ₂ ), lithium manganese oxides (such as LiMnO ₂ , LiMn ₂ O ₄ ), lithium Nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide (such as LiNi _1/3 Co _1/3 Mn _1/3 O ₂ (also referred to as NCM ₃₃₃ ), LiNi _0.5 Co _0.2 Mn _0.3 O ₂ (can also be abbreviated to NCM ₅₂₃ ), LiNi _0.5 Co _0.25 Mn _0.25 O ₂ (can also be abbreviated to NCM ₂₁₁ ), LiNi _0.6 Co _0.2 Mn _0.2 O ₂ (can also be abbreviated to NCM ₆₂₂ ), LiNi At least one of _0.8 Co _0.1 Mn _0.1 O ₂ (also referred to as NCM ₈₁₁ ), lithium nickel cobalt aluminum oxide (such as LiNi _0.85 Co _0.15 Al _0.05 O ₂ ) and its modified compounds. The olivine structure contains Examples of lithium phosphates may include, but are not limited to, lithium iron phosphate (such as LiFePO ₄ (also referred to as LFP)), composites of lithium iron phosphate and carbon, lithium manganese phosphate (such as LiMnPO ₄ ), lithium manganese phosphate and carbon. At least one of composite materials, lithium iron manganese phosphate, and composite materials of lithium iron manganese phosphate and carbon.

In some embodiments, the positive electrode film layer optionally further includes a binder. As examples, the binder may include polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene At least one of ethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer and fluorine-containing acrylate resin.

In some embodiments, the positive electrode film layer optionally further includes a conductive agent. As examples, the conductive agent may include superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphite At least one of alkenes and carbon nanofibers.

In some embodiments, the positive electrode sheet can be prepared by dispersing the above-mentioned components for preparing the positive electrode sheet, such as positive active material, conductive agent, binder and any other components in a solvent (such as N -methylpyrrolidone) to form a positive electrode slurry; the positive electrode slurry is coated on the positive electrode current collector, and after drying, cold pressing and other processes, the positive electrode piece can be obtained.

electrolyte

The electrolyte plays a role in conducting ions between the positive and negative electrodes. The type of electrolyte in this application can be selected according to needs. For example, the electrolyte can be liquid, gel, or completely solid.

In some embodiments, the electrolyte is an electrolyte solution. The electrolyte solution includes electrolyte salts and solvents.

In some embodiments, the electrolyte salt may be selected from the group consisting of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bisfluorosulfonimide, lithium bistrifluoromethanesulfonimide, trifluoromethane At least one of lithium sulfonate, lithium difluorophosphate, lithium difluoroborate, lithium dioxaloborate, lithium difluorodioxalate phosphate and lithium tetrafluoroxalate phosphate.

In some embodiments, the solvent may be selected from the group consisting of ethylene carbonate, propylene carbonate, methylethyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methylpropyl carbonate, ethylpropyl carbonate, Butylene carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate At least one of ester, 1,4-butyrolactone, sulfolane, dimethyl sulfone, methyl ethyl sulfone and diethyl sulfone.

In some embodiments, the electrolyte optionally further includes additives. For example, additives may include negative electrode film-forming additives, positive electrode film-forming additives, and may also include additives that can improve certain properties of the battery, such as additives that improve battery overcharge performance, additives that improve battery high-temperature or low-temperature performance, etc.

Isolation film

In some embodiments, the secondary battery further includes a separator film. The type of isolation film used in this application, Any well-known porous structure isolation membrane with good chemical stability and mechanical stability can be used.

In some embodiments, the material of the isolation membrane can be selected from at least one of glass fiber, non-woven fabric, polyethylene, polypropylene and polyvinylidene fluoride. The isolation film can be a single-layer film or a multi-layer composite film. When the isolation film is a multi-layer composite film, the materials of each layer can be the same or different.

In some embodiments, the positive electrode piece, the negative electrode piece and the separator film can be made into an electrode assembly through a winding process or a lamination process.

In some embodiments, the secondary battery may include an outer packaging. The outer packaging can be used to package the above-mentioned electrode assembly and electrolyte.

In some embodiments, the outer packaging of the secondary battery may be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc. The outer packaging of the secondary battery may also be a soft bag, such as a bag-type soft bag. The material of the soft bag may be plastic, and examples of the plastic include polypropylene, polybutylene terephthalate, polybutylene succinate, and the like.

The shape of the secondary battery of the present application can be cylindrical, square or any other shape. For example, FIG. 1 shows a square-structured secondary battery 5 as an example.

In some embodiments, referring to FIG. 3 , the outer package may include a housing 51 and a cover 53 . The housing 51 may include a bottom plate and side plates connected to the bottom plate, and the bottom plate and the side plates enclose a receiving cavity. The housing 51 has an opening communicating with the accommodation cavity, and the cover plate 53 can cover the opening to close the accommodation cavity. The positive electrode piece, the negative electrode piece and the isolation film can be formed into the electrode assembly 52 through a winding process or a lamination process. The electrode assembly 52 is packaged in the containing cavity. The electrolyte soaks into the electrode assembly 52 . The number of electrode assemblies 52 contained in the secondary battery 5 can be one or more, and those skilled in the art can select according to specific actual needs.

In some embodiments, secondary batteries can be assembled into battery modules, and the number of secondary batteries contained in the battery module can be one or more. Those skilled in the art can select the specific number according to the application and capacity of the battery module.

Figure 4 is a battery module 4 as an example. Referring to Figure 6, in the battery module 4, a plurality of The secondary batteries 5 may be arranged sequentially along the length direction of the battery module 4 . Of course, it can also be arranged in any other way. Furthermore, the plurality of secondary batteries 5 can be fixed by fasteners.

Optionally, the battery module 4 may further include a housing having a receiving space in which a plurality of secondary batteries 5 are received.

In some embodiments, the above-mentioned battery modules can also be assembled into a battery pack. The number of battery modules contained in the battery pack can be one or more. Those skilled in the art can select the specific number according to the application and capacity of the battery pack.

Figures 5 and 6 show the battery pack 1 as an example. Referring to FIGS. 5 and 6 , the battery pack 1 may include a battery box and a plurality of battery modules 4 disposed in the battery box. The battery box includes an upper box 2 and a lower box 3 . The upper box 2 can be covered with the lower box 3 and form a closed space for accommodating the battery module 4 . Multiple battery modules 4 can be arranged in the battery box in any manner.

In addition, the present application also provides an electrical device, which includes at least one of the secondary battery, battery module, or battery pack provided by the present application. The secondary battery, battery module, or battery pack may be used as a power source for the electrical device, or may be used as an energy storage unit for the electrical device. The electric device may include mobile devices (such as mobile phones, laptops, etc.), electric vehicles (such as pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, and electric golf carts). , electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc., but are not limited to these.

As the power-consuming device, a secondary battery, a battery module or a battery pack can be selected according to its usage requirements.

FIG. 7 is an electrical device as an example. The electric device 6 is a pure electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, or the like. In order to meet the high power and high energy density requirements of the secondary battery for the electrical device, a battery pack or battery module can be used.

As another example, the device may be a mobile phone, a tablet, a laptop, etc. The device is usually required to be thin and light, and a secondary battery can be used as a power source.

Hereinafter, examples of the present application will be described. The embodiments described below are illustrative and are only used to explain the present application and are not to be construed as limitations of the present application. If specific techniques or conditions are not specified in the examples, the techniques or conditions described in literature in the field or product instructions will be followed. If the manufacturer of the reagents or instruments used is not indicated, they are all conventional products that can be purchased commercially. It should be noted that any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention shall be included in the protection scope of the present invention.

The following are specific examples.

1. Preparation of secondary batteries

Example 1

1) Preparation of positive electrode plate

Mix LFP: conductive carbon SP: dispersant DS-2: binder PVDF in the following ratio (97.2%: 0.7%: 0.3%: 1.8%), then add NMP solution to form a solid content of about 70% The right slurry is then evenly coated on the 13μm aluminum foil using extrusion coating; then the positive electrode piece is prepared through cold pressing and laser die cutting;

2) Preparation of negative electrode piece

The negative electrode current collector uses 6μm thick copper foil;

The step of forming a second negative active coating layer. Use the second negative active material (artificial graphite): conductive carbon SP: dispersant CMC: binder SBR in the following ratio (96.85%: 0.4%: 1.25%: 1.5%) and mix evenly, then add deionized water and configure Form a slurry with a solid content of about 50%, and then use extrusion coating to coat the surface of the copper foil;

A first negative active coating layer is formed. Use the first negative active material (natural graphite): conductive carbon SP: dispersant CMC: binder SBR in the following ratio (96.65%: 0.7% SP: 1.35%: 1.3%) and mix evenly, then add deionized water. Configure it into a slurry with a solid content of about 50%, and then use extrusion coating to coat the surface of the first layer of negative active material;

The negative electrode piece is then prepared through cold pressing, laser die-cutting and other processes;

3)Isolation film

Use polypropylene film as the isolation film.

4) Preparation of electrolyte

In an argon atmosphere glove box (H ₂ O <0.1ppm, O ₂ <0.1ppm), mix the organic solvent ethylene carbonate (EC)/ethyl methyl carbonate (EMC) evenly according to the volume ratio of 3/7, add 12.5 Dissolve wt% LiPF ₆ lithium salt in an organic solvent and stir evenly to obtain an electrolyte.

5) Preparation of battery

The positive electrode piece, the negative electrode piece and the separator film are rolled to prepare a bare battery core, which is then installed into an aluminum case and prepared through processes such as liquid injection, high temperature standing, formation, aging, and volume separation. Normal lithium-ion battery.

The secondary batteries of Examples 2 to 14 and the secondary batteries of Comparative Examples 1 to 3 are similar to the secondary batteries of Example 1, but the composition and product parameters of the battery pole pieces are adjusted. The different product parameters are detailed in the table 1.

The first negative active material is natural graphite, and its gram capacity varies slightly with Dv50; the details are as follows:

The gram capacity of the first negative active material with Dv50 of 12 μm is 350 mAh/g;

The gram capacity of the first negative active material with Dv50 of 8 μm is 345 mAh/g;

The gram capacity of the first negative active material with Dv50 of 6 μm is 340 mAh/g.

The second negative active material is all artificial graphite, and its gram capacity varies slightly with Dv50; the details are as follows:

The gram capacity of the first negative active material with Dv50 of 15 μm is 360 mAh/g;

The gram capacity of the first negative active material with Dv50 of 9 μm is 347 mAh/g;

The first negative electrode active material with a Dv50 of 17 μm has a gram capacity of 373 mAh/g.

2. Battery performance test

1. Low temperature charging process

The charging method of the secondary battery at ambient temperature T ₀ includes the following steps S10-S20:

Step S10: Perform the rapid thermal charging of the secondary battery from the initial temperature T ₀ at a charging rate of 0.3C to 5C (specific values are shown in Table 1) until the temperature rises ΔT, so that the temperature reaches the target temperature T ₁ ;

Step S20: Continue charging the secondary battery from the target temperature T ₁ to 80% SOC at a charging rate of 0.5C to 5C (specific values are shown in Table 1).

In each embodiment and comparative example in Table 1, the starting SOC (i.e. C _Q ) of step S10 is 10% SOC, and the initial temperature T ₀ (environmental temperature) is -20°C; the charging end SOC (i.e. C ₀ ) are both 80% SOC.

The total charging time in Table 1 is the sum of the charging times in step S10 and step S20.

The polarization voltage of the secondary battery in rapid thermal charging is U _J , and the balance voltage of the secondary battery is _UP ; the units of U _J and _UP are V;

C ₀ '=Q ₁ /(3600U _J -3600U _P ).

U _P refers to the charging voltage of 0.05C at 25℃.

The mass of the secondary battery is denoted by m, and the average specific heat capacity of the secondary battery is denoted by C, then Q ₁ =m*C*ΔT.

The average specific heat capacity C of the secondary battery can be tested by the following method: charge and discharge the secondary battery in an accelerated adiabatic calorimeter (ARC) or homemade adiabatic equipment, and record the voltage, temperature, charge and discharge time and other data of the secondary battery. , and then based on the battery thermal theoretical model proposed by Newman et al., the heat energy Q ₂ of the secondary battery was theoretically calculated, and finally the average specific heat capacity C of a single secondary battery was back calculated through the formula Q ₂ =C m△T. Then Q ₁ can be obtained through Q ₁ =m*C*ΔT; and C ₀ ' can be obtained according to C ₀ '= Q ₁ / (3600U _J -3600U _P ). C ₀ ' is shown in Table 1.

In Table 1, C ₁ =m ₁ ×a, where the total mass of the first negative active material is recorded as m ₁ in g; the gram capacity of the first negative active material is recorded as a in A·h/g;

C ₂ =m ₂ ×b, where the total mass of the second negative active material is recorded as m ₂ and the unit is g; the gram capacity of the second negative active material is recorded as b and the unit is A·h/g;

The total capacity of the secondary battery is recorded as C _Z , and the unit is A·h; C _Z =C ₁ +C ₂ . In this way, C ₁ /C _Z and C ₂ /C _Z can be obtained.

2. Lithium precipitation performance test

Each secondary battery that reaches 80% SOC according to the above low-temperature charging process will be disassembled to observe whether lithium is precipitated at the interface of the negative electrode piece.

The evaluation method for the degree of lithium precipitation is as follows:

No lithium precipitation: There is no lithium precipitation area in the entire negative electrode piece;

Slight lithium precipitation: the maximum area of a single lithium precipitation area in the entire negative electrode piece is ≤5*5mm ² , and the number of lithium precipitation areas in the entire negative electrode piece is ≤1;

Moderate lithium precipitation: 5*5mm ² <The maximum area of a single lithium precipitation area of the entire negative electrode piece is ≤10*10mm ² , and the number of lithium precipitation areas of the entire negative electrode piece is ≤1;

Severe lithium evolution: Lithium evolution exists and does not meet the criteria for mild lithium evolution and moderate lithium evolution.

3. Energy density test

Conduct a 1/3C capacity test on the battery core at 25°C, that is, charge it at 1/3C first, and then discharge it. Repeat this step 3 times, record the third discharge energy, and simultaneously measure the length and width of the battery core. If Q is high, record the cell volume V. The ratio of the discharge energy Q to the cell volume V is the battery energy density.

3. Analysis of test results of each embodiment and comparative example

Batteries of each example and comparative example were prepared according to the above method, and various performance parameters were measured. The results are shown in Table 1 below.

Among them, the symbols in Table 1 have the same meaning as in the instructions.

Table 1

The negative electrode plates of the secondary batteries of Comparative Example 1 and Comparative Example 2 only contained the second negative electrode active coating, and the first negative electrode active coating was omitted. Comparative Example 1 adopts the same low-temperature charging process as Example 3. The results show that the secondary battery of Comparative Example 1 has severe lithium deposition. The secondary battery of Comparative Example 2 is the same as Comparative Example 1, but the low-temperature charging process is different. The conventional charging process is used. The results show that no lithium is evaporated, but there is a shortcoming of long charging time. The charging time is several times that of the embodiment. .

The structure of the negative electrode plate of the secondary battery of Comparative Example 3 is basically the same as that of the secondary battery of Example 3. The only difference is that in Comparative Example 3, the capacity C ₀ charged by the negative electrode plate during the rapid thermal charging stage is larger, and thus Make C ₁ <C ₀ , resulting in serious lithium precipitation.

Specifically, Examples 1 to 3 are basically the same, the only difference is that the Dv50 particle size of the first negative electrode active material is different, and the corresponding gram capacity is also different; as the Dv50 particle size of the first negative electrode active material decreases, the first negative electrode The kinetic properties of the active coating are improved, the lithium precipitation problem is improved, and the gram capacity is reduced, resulting in a slight reduction in battery energy density.

Embodiments 3 to 5 are basically the same. The only difference is that the porosity of the first negative electrode active coating is different. Specifically, different porosity is obtained by controlling the cold pressing process in the preparation process of the negative electrode sheet; as the porosity increases, The problem of lithium precipitation has been improved, and the battery energy density has been slightly reduced.

Embodiments 3, 6 to 7 are basically the same, the only difference lies in the content added in the first negative electrode active coating The amount of the first negative active material is different, thus making C ₁ /C _Z different, 2C ₀ ≥ _{C 1} ≥ _{C 0} . Examples 3 and 6 control 1.5C ₀ ≥ C ₁ ≥ _{C 0} , and the degree of lithium evolution is lower than Example 7, which controls C ₁ =2C ₀ . According to the energy density and lithium deposition performance of the battery, optionally, 1.5C ₀ ≥C ₁ ≥C ₀ .

Embodiments 3, 8 to 9 are basically the same, the only difference is that the Dv50 particle size of the second negative electrode active material is different, and the corresponding gram capacity is also different; as the Dv50 particle size of the second negative electrode active material decreases, the second negative electrode active material The kinetic properties of the coating are improved, the lithium precipitation problem is improved, and the gram capacity is reduced, resulting in a slight reduction in battery energy density.

Embodiments 3 and 10 to 11 are basically the same. The only difference is that the porosity of the second negative electrode active coating is different. Specifically, different porosity is obtained by controlling the cold pressing process in the preparation process of the negative electrode piece; as the porosity increases, With the increase, the lithium precipitation problem is improved and the battery energy density is slightly reduced.

Embodiments 3 and 12 to 13 are basically the same. The only difference lies in the rate of rapid thermal charging. The battery energy density of the battery is maintained at a better level and the lithium deposition problem is improved. Taking into account the lithium deposition situation and the charging time, the rapid thermal charging rate of Embodiment 3 can be selected.

Embodiment 14 is basically the same as Embodiment 3, in which the rapid thermal charging rate is the same and the SOC at the end of controlled rapid heating is different. Comparison shows that although lithium precipitation does not occur in Embodiment 14, the total charging time is longer.

It should be noted that the present application is not limited to the above-described embodiment. The above-mentioned embodiments are only examples. Within the scope of the technical solution of the present application, embodiments that have substantially the same structure as the technical idea and exert the same functions and effects are included in the technical scope of the present application. In addition, within the scope that does not deviate from the gist of the present application, various modifications to the embodiments that can be thought of by those skilled in the art, and other forms constructed by combining some of the constituent elements in the embodiments are also included in the scope of the present application. .

Claims (22)

1. A secondary battery, including a negative electrode sheet, the negative electrode sheet includes a negative electrode current collector, a first negative electrode active coating and a second negative electrode active coating, the first negative electrode active coating is provided on the negative electrode current collector On at least one surface of the negative electrode active coating, the second negative electrode active coating is disposed between the first negative electrode active coating and the negative electrode current collector, and the resistance of the first negative electrode active coating is smaller than that of the second negative electrode active coating. The resistance of the coating, the capacity of the first negative active coating is recorded as C ₁ ;

   The secondary battery is rapidly thermally charged from the initial temperature T ₀ at a charging rate of 0.3C to 5C until the temperature rises ΔT. The capacity of the secondary battery at the end of the rapid thermal charging is recorded as C ₀ ; T ₀ is - 20℃～0℃, ΔT≥5℃;

   The secondary battery satisfies: C ₁ ≥ _{C 0} .
2. The secondary battery according to claim 1, wherein the secondary battery satisfies: 2C ₀ ≥ C ₁ ≥ _{C 0} .
3. The secondary battery according to claim 2, wherein the secondary battery satisfies: 1.5C ₀ ≥ C ₁ ≥ _{C 0} .
4. The secondary battery according to any one of claims 1 to 3, wherein the temperature of the secondary battery is increased by ΔT to a target temperature T ₁ , and T ₁ is -10°C to 15°C.
5. The secondary battery according to any one of claims 1 to 4, wherein _T1 is -10°C to 5°C.
6. The secondary battery according to any one of claims 1 to 5, wherein T ₀ is -20°C to -10°C.
7. The secondary battery according to any one of claims 1 to 6, wherein ΔT≥10°C.
8. The secondary battery according to any one of claims 1 to 7, wherein the first negative active coating includes a first negative active material, and the total mass of the first negative active material is expressed as m ₁ , and the unit is g; the gram capacity of the first negative active material is recorded as a, and the unit is A·h/g;

   Then m ₁ =C ₁ /a.
9. The secondary battery according to claim 8, wherein the unit of C ₁ is A·h, and the total capacity of the secondary battery is recorded as C _Z , and the unit is A·h;

   C ₁ /C _Z =30% to 60%.
10. The secondary battery according to claim 9, wherein C ₁ /C _Z =30% to 40%.
11. The secondary battery according to claim 9, wherein the capacity of the second negative active coating is denoted as C ₂ and the unit is A·h;

    The second negative active coating includes a second negative active material. The total mass of the second negative active material is m ₂ in g. The gram capacity of the second negative active material is b in unit. A·h/g;

    Then C ₂ =C _Z -C ₁ ; m ₂ =C ₂ /b.
12. The secondary battery according to claim 11, wherein the first negative active material is selected from at least one of natural graphite, soft carbon, hard carbon and coated graphite, and the coating of the coated graphite The layer contains at least one of soft carbon and hard carbon, and the second negative active material is selected from artificial graphite.
13. The secondary battery according to any one of claims 11 to 12, wherein the average volume particle diameter Dv50 of the first negative electrode active material is smaller than the average volume particle diameter Dv50 of the second negative electrode active material.
14. The secondary battery according to claim 13, wherein the average volume particle size Dv50 of the first negative active material is 3 to 12 μm, optionally 6 to 12 μm.
15. The secondary battery according to any one of claims 13 to 14, wherein the second negative electrode active material has an average volume particle diameter Dv50 of 9 to 17 μm.
16. The secondary battery according to any one of claims 11 to 15, wherein the porosity of the first negative active coating is greater than the porosity of the second negative active coating.
17. The secondary battery of claim 16, wherein the first negative active coating has a porosity of 25% to 40%.
18. The secondary battery according to any one of claims 16 to 17, wherein the second negative electrode active coating has a porosity of 20% to 30%.
19. The secondary battery according to any one of claims 1 to 18, wherein the secondary battery The charging method at temperature T ₀ includes the following steps S10-S20:

    Step S10: The secondary battery is charged rapidly from the initial temperature T ₀ at a charging rate of 0.3C to 5C until the temperature rises ΔT, so that the temperature reaches the target temperature T ₁ ;

    Step S20: The secondary battery continues to be charged from the target temperature T ₁ to 80% SOC to 100% SOC at a charging rate of 0.5C to 5C.
20. The secondary battery according to any one of claims 1 to 19, wherein the unit of C ₁ is A·h;

    The theoretical heat required for the rapid thermal charging is recorded as Q ₁ , and the unit of Q ₁ is J;

    The polarization voltage of the secondary battery in the rapid thermal charging is U _J , and the balance voltage of the secondary battery is _UP ; the units of U _J and _UP are V; the rapid thermal charging charges The capacity of the above-mentioned secondary battery is recorded as C ₀ ';
    C ₀ '=Q ₁ /(3600U _J -3600U _P ).
21. The secondary battery according to claim 20, wherein the mass of the secondary battery is denoted by m, and the average specific heat capacity of the secondary battery is denoted by C, then Q ₁ =m*C*ΔT.
22. An electrical device comprising a secondary battery selected from any one of claims 1 to 21.