WO2023240612A1

WO2023240612A1 - Negative electrode plate, secondary battery, battery module, battery pack, and electric device

Info

Publication number: WO2023240612A1
Application number: PCT/CN2022/099515
Authority: WO
Inventors: 柴志生; 迟庆魁; 金海族
Original assignee: 宁德时代新能源科技股份有限公司
Priority date: 2022-06-17
Filing date: 2022-06-17
Publication date: 2023-12-21
Also published as: CN117941092A

Abstract

The present application relates to a negative electrode plate. The negative electrode plate comprises: a current collector; a first negative electrode material layer, which is arranged on at least one surface of the current collector and comprises a first negative electrode active material; and a second negative electrode material layer, which is arranged on the first negative electrode material layer and comprises a second negative electrode active material, wherein the first negative electrode material layer has a porosity Q1, the second negative electrode material layer has a porosity Q2, and 1.11≤Q2/Q1≤1.45. In addition, the present application further relates to a secondary battery, a battery module, a battery pack and an electric device, which comprise the negative electrode plate. The negative electrode plate, the secondary battery, the battery module, the battery pack and the electric device of the present application have improved battery capacity and charging performance.

Description

Negative electrode plates, secondary batteries, battery modules, battery packs and electrical devices

Technical field

The present application relates to the technical field of lithium batteries, and in particular to a negative electrode plate, a secondary battery, a battery module, a battery pack and an electrical device including the negative electrode plate.

Background technique

After lithium-ion batteries are widely used in new energy vehicles, people are paying attention to issues such as the vehicle's cruising range and charging time, which have put forward higher requirements for the battery capacity and fast charging capabilities of lithium-ion batteries.

However, for a long time, in lithium-ion batteries, high battery capacity and fast charging performance have always seemed to be "can't have both": high battery capacity often means that its fast charging performance is restricted; while improving fast charging performance Commonly used methods often reduce battery capacity. Therefore, an ideal lithium-ion battery should have a balance of high battery capacity and fast charging performance. Therefore, how to make the negative electrode plate have both a higher battery capacity and a faster charging speed is an urgent problem to be solved in the field.

Contents of the invention

This application was made in view of the above-mentioned problems, and its purpose is to provide a negative electrode plate, a secondary battery, a battery module, a battery pack and a power consumption device with good battery capacity and fast charging performance.

In order to achieve the above purpose, this application provides a negative electrode plate, which includes:

current collector,

a first negative electrode material layer disposed on at least one surface of the current collector, the first negative electrode material layer including a first negative electrode active material;

a second negative electrode material layer disposed on the first negative electrode material layer, the second negative electrode material layer including a second negative electrode active material;

The first negative electrode material layer has a porosity Q1, the second negative electrode material layer has a porosity Q2, and 1.11≤Q2/Q1≤1.45.

Therefore, the negative electrode plate of the present application can enable the secondary battery to have both high battery capacity and good fast charging performance (such as short charging time), achieving a balance between the two.

In any embodiment, 1.18≤Q2/Q1≤1.45. Keeping Q2/Q1 within the above range can further improve the battery capacity and fast charging performance of the secondary battery.

In any embodiment, the first negative electrode material layer has a porosity Q1 of 15% to 35%, optionally 20% to 30%.

In any embodiment, the porosity Q2 of the second negative electrode material layer is 20% to 40%, optionally 25% to 35%.

When the porosity of the first and second negative electrode material layers are respectively within the above range, it is beneficial to improve the battery capacity and fast charging performance.

In any embodiment, the first negative active material has a median particle diameter of D1, the second negative active material has a median particle diameter of D2, and 0.4≤D2/D1≤0.95, optionally 0.6≤ D2/D1≤0.8. The material particle size ratio within the above range helps lithium ions in the electrolyte quickly enter the negative electrode material layer, which is beneficial to improving fast charging performance and shortening charging time.

In any embodiment, the friction coefficient of the first negative active material is μ1, the friction coefficient of the second negative active material is μ2, and 1≤μ2/μ1≤2, optionally 1.1≤μ2/μ1≤1.7 . By controlling the friction coefficient of each layer of negative active material, it is more conducive to further increasing the battery capacity of the secondary battery and improving its fast charging performance.

In any embodiment, the compressive strength of the first negative active material is P1, the compressive strength of the second negative active material is P2, and 1.1≤P2/P1≤2.5, optionally 1.1≤P2/ P1≤2.0; the compressive strength is the pressing pressure per unit area when the negative active material is pressed into a compact with a compacted density of 1.7g/ ^cm3 . The use of negative active materials with the above compressive strength is conducive to further increasing the battery capacity of secondary batteries and improving their fast charging performance.

In any embodiment, the first negative active material has a resistivity of ρ1, the second negative active material has a resistivity of ρ2, and 1≤ρ2/ρ1≤1.5, optionally 1.2≤ρ2/ρ1≤ 1.4. When the resistivities of the first and second negative electrode active materials have the above relationship, the resistance of the electrode piece can be reduced, which is beneficial to further improving the fast charging performance of the secondary battery.

In any embodiment, the first negative active material and the second negative active material are the same or different, and are each independently selected from: carbon-based negative active materials, transition metal oxides or combinations thereof, or carbon-based negative active materials. The combination of materials and silicon-based negative active materials, or the combination of transition metal oxides and silicon-based negative active materials;

Optionally, the carbon-based negative active material is selected from graphite, soft carbon, hard carbon or a combination thereof;

Optionally, the transition metal oxide is selected from lithium titanate, lithium niobate, lithium ferrite or combinations thereof;

Optionally, the silicon-based negative active material is selected from elemental silicon, silicon-oxygen composite, silicon-carbon composite, silicon-nitride composite, silicon alloy or combinations thereof.

Choosing the above materials not only ensures good battery capacity, but also helps improve the fast charging performance of the battery.

In any embodiment, the second negative electrode material layer includes 0 to 25 wt%, optionally 0 to 10 wt% of silicon-based negative active material, based on the total weight of the second negative active material count.

In any embodiment, the first negative electrode material layer includes 0 to 25 wt%, optionally 0 to 10 wt% of silicon-based negative active material, based on the total weight of the first negative active material count.

As mentioned above, including silicon-based negative active material in the first and/or second negative electrode material layer can reduce the coating weight of the negative electrode sheet, increase battery capacity, and increase the porosity of each material layer.

A second aspect of the present application also provides a secondary battery, which includes the negative electrode plate of the first aspect of the present application.

A third aspect of the present application further provides a battery module, which includes the secondary battery of the second aspect of the present application.

A fourth aspect of the present application also provides a battery pack, which includes the battery module of the third aspect of the present application.

A fifth aspect of the present application also provides an electrical device, which includes at least one selected from the secondary battery of the second aspect, the battery module of the third aspect, or the battery pack of the fourth aspect.

The negative electrode plate of the present application and the secondary battery including the negative electrode plate have better overall performance, that is, higher battery capacity and better fast charging performance.

Description of the drawings

Figure 1 is a schematic diagram of the negative electrode plate of the present application.

Figure 2 is a scanning electron microscope image of the negative electrode plate of the present application.

FIG. 3 is a schematic diagram of a secondary battery according to an embodiment of the present application.

FIG. 4 is an exploded view of the secondary battery according to the embodiment of the present application shown in FIG. 3 .

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

Figure 6 is a schematic diagram of a battery pack according to an embodiment of the present application.

FIG. 7 is an exploded view of the battery pack according to an embodiment of the present application shown in FIG. 6 .

FIG. 8 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 top cover assembly

Detailed ways

Hereinafter, embodiments specifically disclosing the negative electrode tab, secondary battery, battery module, battery pack, and electrical device of the present application will be described in detail with reference to the accompanying 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 the present application can be performed sequentially or randomly, and are preferably performed 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).

After secondary batteries are widely used in new energy vehicles, people are paying attention to issues such as the vehicle's cruising range and charging time, which have put forward higher requirements for battery capacity and fast charging capabilities. An ideal secondary battery should have both high battery capacity and fast charging performance.

However, for a long time, the high battery capacity and good fast charging performance of batteries have always seemed to be "can't have both." On the one hand, high battery capacity often means that its fast charging performance is restricted, and common methods to improve fast charging performance often reduce battery capacity. On the other hand, although selecting negative active materials with high battery capacity is an effective means to achieve high battery capacity, in many cases it cannot effectively improve fast charging performance.

Therefore, how to make the negative electrode plate have both a higher battery capacity and a faster charging speed is an urgent problem to be solved in the field.

In view of this problem, the present application provides a negative electrode plate, as well as a secondary battery, a battery module, a battery pack and an electrical device including the negative electrode plate.

Negative pole piece

In one embodiment of the present application, the present application proposes a negative electrode sheet, which includes:

current collector,

Without wishing to be bound by any theory, designing the negative electrode plate into a multi-layer structure will help improve the fast charging performance of the battery. In particular, when the negative electrode sheet has, for example, two negative electrode active material layers, and the porosity of each layer satisfies the above range, the secondary battery can have balanced performance—higher capacity and better performance. Fast charging performance.

Q2/Q1 meets the above range, and the battery capacity and fast charging performance reach a better level. This is because during the charging process of the secondary battery, lithium ions from the positive electrode first reach the surface layer of the negative electrode material. At this time, the concentration of lithium ions around the active material in the surface layer (or described as the upper layer, that is, the second negative electrode material layer) is higher. When the surface material has a large porosity, the lithium ions in the electrolyte can be quickly transported to the bottom layer (or described as the lower layer), reducing the lithium ion concentration in the surface layer; and when the surface layer has a large porosity, the ratio of the surface material The surface area is also larger, and lithium ions can quickly migrate from the electrolyte into the solid-phase material (i.e., the negative electrode material), reducing the lithium ion concentration on the surface and preventing lithium ions from being enriched and precipitated on the surface, thereby improving charging capacity. When charging, the lithium ion concentration around the active material in the bottom layer is lower than that in the surface layer, so the porosity of the bottom layer can be relatively low to meet higher capacity. At the same time, such a porosity relationship is also conducive to the effective infiltration of the electrolyte into the lower negative electrode active material, improving the resistance of the electrode piece, avoiding or mitigating the precipitation of active ions in the lower negative electrode active material, and further improving the performance of the electrode piece and secondary battery. In addition, Q2/Q1 meeting the above range can also ensure that the electrode material layer contains an appropriate amount of active material, so that the electrode and the secondary battery have good battery capacity.

In this article, for the convenience of explanation, when the negative electrode sheet has, for example, a two-layer structure, the negative electrode material layer close to the current collector is defined as the lower layer (corresponding to the first negative electrode material layer), and the negative electrode material far away from the current collector is defined as the lower layer (corresponding to the first negative electrode material layer). The layer is defined as the upper layer (corresponding to the second negative electrode material layer).

In some embodiments, the value of Q2/Q1 may be 1.11, 1.18, 1.27, 1.3, 1.36, or 1.45, or a range consisting of any two thereof.

In some embodiments, the porosity Q1 and Q2 satisfy 1.18≤Q2/Q1≤1.45. Keeping the porosity ratio of the first and second negative electrode material layers within the above range helps to further improve and balance the battery capacity and fast charging performance.

In some embodiments, the porosity Q1 of the first negative electrode material layer is 15% to 35%, optionally 20% to 30%. In some embodiments, the porosity Q2 of the second negative electrode material layer is 20% to 40%, optionally 25% to 35%. When the porosity of the first and second negative electrode material layers are respectively within the above range, the charging time can be shortened and the secondary battery can have the required battery capacity; at the same time, it can also help to improve the adhesion of the electrode piece, Reduce ohmic impedance.

In some embodiments, the first negative active material has a median particle diameter of D1, the second negative active material has a median particle diameter of D2, and 0.4≤D2/D1≤0.95, optionally 0.6≤ D2/D1≤0.8. In some embodiments, the value of D2/D1 may be a range of 0.4, 0.57, 0.6, 0.64, 0.68, 0.8, 0.95, or any two thereof. In some embodiments, 0.57≤D2/D1≤0.8; in some embodiments, 0.64≤D2/D1≤0.8. D2/D1 within the above range helps lithium ions in the electrolyte quickly enter the negative electrode material layer, which is beneficial to improving fast charging performance and shortening charging time.

It can be seen from the above that in the negative electrode sheet of the present application, the particle size of the negative active material contained in the upper layer and the lower layer is D2<D1, that is, the particle size of the negative active material in the upper layer is relatively small, while the particle size of the negative active material in the lower layer is relatively small. larger. It is known that the solid-phase diffusion coefficient of active ions in secondary batteries in the negative active material is small. During the charging process, the active ions may be enriched on the surface of the negative active material layer, which is not only detrimental to fast charging but may also cause other problems. Using materials with smaller particle sizes in the upper layer can help reduce or avoid the enrichment and precipitation of active ions, thereby improving fast charging performance.

As used herein, the term "median particle size" (D _v 50) means the particle size at which the cumulative particle size distribution percentage of a sample reaches 50%. The median particle size can be measured by methods well known in the art. For example, the median particle size can refer to the national standard GB/T19077-2016 and be measured using a laser diffraction particle size analyzer.

In some embodiments, the first negative active material has a median particle diameter D1 of 8 μm to 22 μm, optionally 12 μm to 21 μm, and more optionally 16 μm to 21 μm. In some embodiments, the second negative active material has a median particle diameter D2 of 1 μm to 20 μm, optionally 8 μm to 17 μm, and more optionally 11 μm to 13 μm.

In some embodiments, the D1 ranges from 8 μm to 22 μm, and the D2 ranges from 1 μm to 20 μm. In some embodiments, the D1 is from 12 μm to 21 μm, and the D2 is from 8 μm to 17 μm. D1 and D2 respectively meet the above range and can further improve battery capacity and fast charging performance.

In some embodiments, the friction coefficient of the first negative active material is μ1, the friction coefficient of the second negative active material is μ2, and 1≤μ2/μ1≤2, optionally 1.1≤μ2/μ1≤1.7 . In some embodiments, the value of μ2/μ1 may be 1, 1.1, 1.43, 1.7, or 2, or a range consisting of any two thereof. μ2/μ1 satisfying the above range is beneficial to improving battery capacity, improving electrolyte infiltration, reducing impedance, and improving fast charging performance.

The coefficient of friction can be determined using methods known in the art. For example, the friction coefficient can be determined as follows: press the negative active material to be tested into two pieces, measure the mass of one sample as m, and then stack the two pieces to be tested. The sample is located on the upper layer, and the lower sample is fixed so that the contact surfaces overlap. Push the sample placed on the upper layer horizontally at a speed of 1mm/s, and record the stable thrust as F. The friction coefficient μ is calculated by the formula μ=F/(m×g) (where g is the gravity constant, g=9.8N/kg).

In some embodiments, the friction coefficient of the first negative active material is μ1, and μ1 is 0.02-0.4, optionally 0.05-0.4, more optionally 0.05-0.3. In some embodiments, the friction coefficient of the second negative active material is μ2, and μ2 is 0.05-0.6, optionally 0.1-0.5, more optionally 0.2-0.4. Selecting the first and second negative active materials with friction coefficients within the above range is more conducive to further improving the performance of the pole piece and battery.

In some embodiments, the compressive strength of the first negative active material is P1, the compressive strength of the second negative active material is P2, and 1.1≤P2/P1≤2.5, optionally 1.1≤P2/ P1≤2.0; the compressive strength is the pressing pressure per unit area when the negative active material is pressed into a compact with a compacted density of 1.7g/ ^cm3 . In this application, the unit of compressive strength is MPa. In some embodiments, the value of P2/P1 may be 1.1, 1.2, 2.0, or 2.5, or a range consisting of any two thereof. In some embodiments, 1.2≤P2/P1≤2.0. The compressive strength of each layer of negative active material satisfies the above relationship, which is conducive to further improving the performance of the pole piece and battery.

The compressive strength can be determined by referring to the method of GB/T 13465.2-2002. For example, the compressive strength can be measured by the following method: weigh a certain mass of the material to be measured, put it evenly into a hollow cylindrical tank with an internal cross-sectional area S, and use a pressure head (the cross-sectional area is also S) to gradually push the material Press to a certain thickness so that the compacted density is 1.7g/cm ³ and record the pressure as F at this time. The compressive strength P is calculated by the formula P=F/S.

In some embodiments, the compressive strength of the first negative active material is P1, and P1 is 60MPa to 200MPa, optionally 65MPa to 175MPa, more optionally 70MPa to 80MPa. In some embodiments, the compressive strength of the second negative active material is P2, and P2 is 75MPa to 265MPa, optionally 82.5MPa to 262.5MPa, more optionally 90MPa to 210MPa. The use of negative active materials with the above-mentioned compressive strength is conducive to further improving the performance of the pole piece and battery.

Without wishing to be bound by any theory, it has been found that controlling D2/D1, μ2/μ1 and P2/P1 simultaneously within the above ranges can further improve pole piece performance.

In some embodiments, the first negative active material has a resistivity of ρ1, the second negative active material has a resistivity of ρ2, and 1≤ρ2/ρ1≤1.5, optionally 1.2≤ρ2/ρ1≤ 1.5, optionally 1.2≤ρ2/ρ1≤1.4. In some embodiments, the value of ρ2/ρ1 may be 1, 1.2, 1.4, or 1.5, or a range consisting of any two thereof. Choosing such a material can further improve the fast charging performance of the negative electrode piece and reduce the resistance of the entire electrode piece and even the battery.

In some embodiments, the first negative active material has a resistivity ρ1 of 8×10 ^-6 to 15×10 ^-6 Ω·m, optionally 9×10 ^-6 to 13×10 ^-6 Ω·m , more optionally 10×10 ^-6 to 12×10 ^-6 Ω·m. In some embodiments, the resistivity ρ2 of the second negative active material is 7×10 ^-6 to 18×10 ^-6 Ω·m, optionally 11×10 ^-6 to 16×10 ^-6 Ω· m, more optionally 12×10 ^-6 to 15×10 ^-6 Ω·m.

In this article, "resistivity" means a physical quantity used to measure the electron transport resistance characteristics of a substance. Resistivity can be determined by methods well known in the art. For example, the resistivity of the negative active material can be measured using a four-probe resistivity tester.

In some embodiments, the first negative active material and the second negative active material are the same or different, and are each independently selected from: carbon-based negative active materials, transition metal oxides or combinations thereof, or carbon-based negative active materials. A combination of materials and silicon-based negative active materials, or a combination of transition metal oxides and silicon-based negative active materials. Selecting the above materials will help improve the fast charging performance of the battery while ensuring battery capacity. In particular, when a combination of a carbon-based negative active material and a silicon-based negative active material or a combination of a transition metal oxide and a silicon-based negative active material is used as the first or second negative active material (especially the second negative active material), Due to the significant volume change characteristics of the silicon-based negative active material during the insertion-extraction process of active ions, the porosity is further improved, thereby improving the fast charging performance.

In some embodiments, optionally, the first negative active material is selected from carbon-based negative active materials, lithium titanate, or combinations thereof. In some embodiments, optionally, the second negative active material is selected from a combination of a carbon-based negative active material and a silicon-based negative active material or a combination of a transition metal oxide and a silicon-based negative active material. In some embodiments, the second negative electrode material layer includes a silicon-based negative electrode material, and the first negative electrode material layer does not include a silicon-based negative electrode material. In some embodiments, both the first negative electrode material layer and the second negative electrode material layer include silicon-based negative electrode materials.

In some embodiments, optionally, the carbon-based negative active material is selected from graphite, soft carbon, hard carbon, or combinations thereof. In some embodiments, optionally, the transition metal oxide is selected from lithium titanate, lithium niobate, lithium ferrite, or combinations thereof. In some embodiments, optionally, the silicon-based negative active material is selected from elemental silicon, silicon oxygen composite (SiOx), silicon carbon composite, silicon nitrogen composite, silicon alloy or combinations thereof. In some embodiments, optionally, the first negative active material is graphite. In some embodiments, optionally, the second negative active material is graphite. The graphite may be artificial graphite or natural graphite. Selecting the above-mentioned materials as the first and/or second negative electrode active materials is beneficial to improving the fast charging performance and battery capacity of the secondary battery.

In some embodiments, the second negative electrode material layer includes 0% to 25% by weight, optionally 0% to 9.65% by weight, optionally 0% to 10% by weight silicon-based negative active material, Based on the total weight of the second negative active material. When the second negative electrode material layer includes the above-mentioned amount of silicon-based negative electrode material, the performance of the electrode piece and even the battery is improved. In addition, the above content range can be beneficial to maintaining the integrity of the second negative electrode material layer (ie, the upper layer) (making it less likely to be powdered and delaminated) when containing silicon-based materials, thereby improving the performance of the electrode sheet and battery.

In some embodiments, the first negative electrode material layer includes 0% to 25% by weight, optionally 0% to 9.65% by weight, optionally 0% to 10% by weight silicon-based negative active material, Based on the total weight of the first negative active material.

In some embodiments, the silicon-based negative electrode material has a median particle size of 0.2 μm to 5 μm. In some embodiments, the silicon-based negative electrode material has a friction coefficient of 1 to 3. In some embodiments, the silicon-based negative electrode material has a compressive strength of 50 MPa to 150 MPa. In some embodiments, the silicon-based negative electrode material has a resistivity of 10 ¹ Ω·m to 10 ² Ω·m.

In some embodiments, the first negative electrode material layer and the second negative electrode material layer have ^{an average compacted density of 1.3 to 1.9 g/cm 3} ^.

In some embodiments, the weight of the first negative electrode material layer is 4.5×10 ^-3 to 7×10 ^-3 g/cm ² . In some embodiments, the weight of the second negative electrode material layer is between 4.5×10 ^-3 and 7×10 ^-3 g/cm ² .

In some embodiments, the thickness of the first negative electrode material layer is 50 μm to 90 μm. In some embodiments, the thickness of the second negative electrode material layer is 55 μm to 110 μm. In this article, the thickness of the material layer is the thickness measured after disassembly and measurement of a fresh battery (that is, a battery that has been charged and discharged ≤ 5 times) after being discharged to the lower limit voltage (that is, in this case, all active ions such as lithium ions are released ).

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

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 formed by forming metal materials (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as polypropylene (PP), polyterephthalate It is formed on substrates such as ethylene glycol ester (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

In some embodiments, each negative electrode material layer optionally further includes a binder. The binder may be any binder commonly used in the art. In some embodiments, the binder may be selected from styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), alginic acid At least one of sodium (SA), polymethacrylic acid (PMAA) and carboxymethyl chitosan (CMCS).

In some embodiments, each negative electrode material layer optionally further includes 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 negative electrode material layer optionally also includes other auxiliaries, such as thickeners (such as sodium carboxymethyl cellulose (CMC-Na)) and the like.

In some embodiments, the negative electrode sheet can be prepared by dispersing the above-mentioned components for preparing the negative electrode sheet, such as negative active materials, conductive agents, binders and any other components in a solvent (such as deionized water) to form a negative electrode slurry; the negative electrode slurry is coated on the negative electrode current collector, and after drying, cold pressing and other processes, the negative electrode piece can be obtained.

In another embodiment of the present application, a secondary battery is provided, which includes the negative electrode sheet of the present application.

In yet another embodiment of the present application, a battery module is provided, which includes the secondary battery of the present application.

In yet another embodiment of the present application, a battery pack is provided, which includes the battery module of the present application.

In another embodiment of the present application, an electrical device is provided, which includes at least one selected from the group consisting of a secondary battery, a battery module or a battery pack of the present application.

Hereinafter, the secondary battery, battery module, battery pack and power consumption device of the present application will be described with appropriate reference to the drawings.

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.

[Positive pole 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 the positive electrode active material of the first aspect of the present application.

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. The composite current collector can be formed by forming metal materials (aluminum, aluminum alloys, nickel, nickel alloys, titanium, titanium alloys, silver and silver alloys, etc.) on polymer material substrates (such as polypropylene (PP), polyterephthalate It is formed on substrates such as ethylene glycol ester (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

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 an example, the conductive agent may include at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene and carbon nanofibers.

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. There is no specific restriction on the type of electrolyte in this application, and it 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. There is no particular restriction on the type of isolation membrane 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, with no special restrictions. When the isolation film is a multi-layer composite film, the materials of each layer can be the same or different, and there is no particular limitation.

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.

This application has no particular limitation on the shape of the secondary battery, which can be cylindrical, square or any other shape. For example, Fig. 3 shows a square-structured secondary battery 5 as an example.

In some embodiments, referring to FIG. 4 , 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 5 is a battery module 4 as an example. Referring to FIG. 5 , in the battery module 4 , a plurality of secondary batteries 5 may be arranged in sequence 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.

6 and 7 show the battery pack 1 as an example. Referring to FIGS. 6 and 7 , 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.

Figure 8 is an electrical device as an example. The electric device is a pure electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, etc. In order to meet the needs of the electrical device for high power and high battery capacity of the secondary battery, 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.

Example

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.

1. Preparation of negative electrode plate and secondary battery

1.1 Negative pole piece

The pole piece without adding silicon-based materials is prepared as follows:

(1) The first negative electrode active material graphite, conductive agent (Super.P), dispersant sodium carboxymethylcellulose (CMC-Na), and binder styrene-butadiene rubber (SBR) are in a weight ratio of 96.5:0.7:1.0: 1.8 Mix, then add deionized water to it, mix well, and obtain the first negative electrode material slurry with a solid content of 50% and a viscosity of 9000 mPa·s.

(2) Mix the second negative active material graphite, conductive agent (Super.P), dispersant sodium carboxymethylcellulose, and adhesive styrene-butadiene rubber in a weight ratio of 96.7:0.7:1.0:1.5, and then add ionized water and mix evenly to obtain a second negative electrode material slurry with a solid content of 50% and a viscosity of 9000 mPa·s.

(3) Use a coater to coat the first negative electrode material slurry on one surface of the current collector copper foil (thickness 6 μm), and then coat the second negative electrode material layer on the first negative electrode material layer. The first negative electrode material The areal densities of the second negative electrode material layer and the second negative electrode material layer are both 6×10 ^-3 g/cm ² (that is, the weight ratio of the second negative electrode material layer to the first negative electrode material layer is 5:5). Then apply the slurry on the other surface of the current collector using the same sequence and method. Then it is rolled so that the average compacted density of the negative electrode piece is 1.7g/cm ³ and the thickness is 147 μm. Cut the rolled negative electrode pieces into 71mm wide electrode pieces.

Figure 1 is a schematic diagram of the negative electrode plate of the present application. Figure 2 is a scanning electron microscope image of the negative electrode plate in Example 6 of the present application. In Figure 2, the gray part in the middle is the current collector. On both sides of the current collector are the negative electrode material layers. It can be seen that the negative electrode material layer is in two layers, with the lower layer having smaller porosity and the upper layer having larger porosity.

For the negative electrode sheet added with silicon-based negative electrode material, the preparation method is as follows:

(1) First negative electrode active material graphite, SiOx (x is between 0 and 2), conductive agent (Super.P), dispersant sodium carboxymethylcellulose (CMC-Na), adhesive styrene-butadiene rubber (SBR) is mixed with a weight ratio (96.5-a1): a1:0.7:1.0:1.8 (where a1 is the content of SiOx, see Table 5 for specific values in each embodiment), then add deionized water to it, and mix , the first negative electrode material slurry with a solid content of 50% and a viscosity of 9000 mPa·s was obtained.

(2) The second negative electrode active material graphite, SiOx (x is between 0 and 2), conductive agent (Super.P), dispersant sodium carboxymethyl cellulose, and adhesive styrene-butadiene rubber are used in a weight ratio (96.5 -a2):a2:0.7:1.0:1.8 are mixed (where a2 is the content of SiOx, see Table 5 for specific values in each embodiment), then add deionized water to it, mix well, and obtain a solid content of 50% and a viscosity of 9000mPa·s second negative electrode material slurry.

(3) Use a coater to coat the first negative electrode material slurry on one surface of the current collector copper foil (thickness 6 μm), and then coat the second negative electrode material layer on the first negative electrode material layer. The first negative electrode material The areal densities of the second negative electrode material layer and the second negative electrode material layer are both 4.6×10 ^-3 g/cm ² (that is, the weight ratio of the second negative electrode material layer to the first negative electrode material layer is 5:5). Then apply the slurry on the other surface of the current collector using the same sequence and method. Then it is rolled so that the average compacted density of the negative electrode piece is 1.7g/cm ³ and the thickness is 114 μm. Cut the rolled negative electrode pieces into 71mm wide electrode pieces.

1.2 Positive pole piece

(1) Mix the active material NCM811, conductive agent (conductive carbon black Super.P and carbon nanotubes), and adhesive polyvinylidene fluoride (PVDF) in a weight ratio of 97.5:1.0:0.5:1, and then add solvent to them N-methylpyrrolidone (NMP), and mix well to obtain a cathode material slurry with a solid content of 70% and a viscosity of 10000 mPa·s.

(2) The above-mentioned positive electrode material slurry is coated on the current collector aluminum foil (thickness 13 μm) using a coater, and the surface density of the coating is 182g/m ² . Roll to make the compacted density of the positive electrode piece 3.5g/cm ³ and the thickness 117 μm. Cut the rolled positive electrode pieces into 68mm wide electrode pieces.

1.3 Electrolyte

Mix ethylene carbonate (EC), diethyl carbonate (DEC) and dimethyl carbonate (DMC) in a volume ratio of 5:2:3, and set the temperature to 25°C; then add lithium hexafluorophosphate to it to prepare 1.0 mol /L solution is the electrolyte.

1.4 Secondary battery

The positive electrode piece, the isolation film (polyethylene, thickness 9 μm) and the negative electrode piece are aligned, stacked and tightly attached in order, and then rolled into a cylindrical bare cell. Assemble the bare battery core into the case and inject 55g of electrolyte. After further chemical formation, a secondary battery is obtained.

2. Porosity test

Cut the pole piece to be tested into a square sample with a certain length and width. Measure and calculate the apparent volume V1 of the sample, V1=S×d (where S is the area of the pole piece, in cm ² ; d is the thickness of the pole piece, in cm).

AccuPyc Ⅱ 1340 true density meter is used, referring to the porosity testing method in GB/T 24586-2009, using the helium replacement method, combined with Archimedes' principle and Bohr's law (PV=nRT), to accurately measure the true density of the material being tested. Volume V2, unit cm ³ .

The total porosity of the pole piece Q=(V1-V2)/V1×100% is calculated by the formula.

The coating weight area density of the first negative electrode material layer W1 (unit: g/cm ² ), the coating weight area density of the second negative electrode material layer W2 (unit: g/cm ² ), and the total coating weight area of the pole piece Density W (unit: g/cm ² ). The thickness d1 (unit cm) of the first negative electrode material layer and the thickness d2 (unit cm) of the second negative electrode material layer were measured through scanning electron microscopy. Calculate the porosity of each layer of pole pieces according to the following formula:

The porosity of the first negative electrode material layer is

Porosity of the second negative electrode material layer

The porosity of the pole piece described in this application is tested after the pole piece is cleaned and dried after the fresh battery is fully discharged.

3. Particle size test

Referring to the national standard GB/T19077-2016, a Mastersizer 3000 laser diffraction particle size analyzer (Malvern Panalytical) was used. Deionized water was used as the solvent. The positive active material to be tested was sonicated for 5 minutes before testing.

4. Resistivity test

(1) Resistivity of negative active material

Suzhou Lattice ST2722 resistivity tester was used, and a 0.9g sample was placed in the feeding cup of the resistivity tester. The resistivity of the negative active material was measured by the four-probe method, and pressure was applied (4, 8, 12 , 16MPa), record the resistivity test results at different pressure points, and take the average value for calculation.

(2) Resistivity of pole piece

The testing instrument is GDW3-KDY-2 two-probe diaphragm resistance tester (Beijing Zhonghui Tiancheng Technology). Take the pole piece to be tested or prepare the pole piece layer to be tested and make a 4cm×25cm sample. The samples were vacuum dried at 85°C for more than 4 hours and tested using the above resistance tester. The test pressure is 0.2-0.4MPa.

5. Friction coefficient test

Press the negative electrode active material to be tested into a 50cm×50cm×5cm sample to be tested (without using adhesive), with a density of 2.0g/cm ³ . There are two pieces in total. One of the samples is weighed, and the measured mass is m, then stack the two samples to be tested, place the weighed sample on the upper layer, and fix the sample on the lower layer so that the contact surfaces overlap. Push the sample placed on the upper layer horizontally at a speed of 1mm/s, and record the stable thrust as F. The friction coefficient μ is calculated by the formula μ=F/(m×g) (where g is the gravity constant, g=9.8N/kg).

6. Compressive strength (P) test

Refer to the method recorded in GB/T 13465.2-2002 to test the compressive strength of the material. Weigh 2.618g of the negative active material to be measured, put it evenly into a hollow cylindrical tank with an internal cross-sectional area S= ^154.025mm2 , and use a pressure head (cross-sectional area of ^154.025mm2 ) to gradually press the negative active material until the thickness is 10mm, so that the compacted density at this time is 1.7g/cm ³ , and the pressure at this time is recorded as F with a high-speed rail tensile machine (model CMT5504). The compressive strength P is calculated by the formula P=F/S.

7. Charging time and battery capacity test

The full battery is charged with a stepped decreasing current at 35°C. The battery state of charge (SOC) ranges from 10% to 80% SOC. The boundary condition is that the negative electrode potential is >0mV. The test equipment is Xinwei charger and discharger. The specific testing process is as follows:

1. Prepare the battery to be tested: Prepare the secondary battery as described above, place the lithium-plated copper wire outside the wound bare battery core, and wrap it with an isolation film to prevent it from overlapping with the pole piece or case. , lead the copper wire out of the battery core as the third electrode;

2. Connect the prepared positive and negative poles of the battery to be tested to the charging and discharging wires of the Xinwei charger and discharger. First, use the following method to test the discharge capacity: (1) Charge the battery to 4.25V at 0.33C, then charge at a constant voltage until the current drops to 0.05C; (2) Leave it aside for 30 minutes; (3) Discharge to 2.5V at 0.33C, and record The capacity during this discharge process is the real capacity C0;

3. Use a voltage acquisition device to record the voltage between the third electrode and the negative electrode post, which is the "negative electrode potential". Adjust the initial SOC of the battery to 10%, and then charge the battery using the stepped reduction current charging method. Specifically, set the initial charging rate to 3C0. When the negative electrode potential drops to 0mV, reduce the charging rate to (3-x)C0, where x = 0.05C0. Continue charging until the anode potential drops to 0mV, and then reduce the charging rate. is (3-2*x)C0, where x=0.05C0, and so on until charged to 80% SOC. In this example, x=0.05, and the total time for charging from 10% SOC to 80% SOC is recorded.

Table 1

Table 1 shows the effects of porosity Q2, Q1 and particle size D2, D1 in the negative electrode sheet on battery performance. Among them, in Examples 1-9 and Comparative Examples 1-2, the friction coefficient μ, compressive strength P and resistivity ρ of the material for preparing the negative electrode piece are respectively:

First material layer: μ1 is 0.27, P1 is 75MPa, ρ1 is 10×10 ^-6 Ω·m;

Second material layer: μ2 is 0.3, P2 is 90MPa, ρ2 is 12×10 ^-6 Ω·m;

Furthermore, μ2/μ1 is 1.11, P2/P1 is 1.2, and ρ2/ρ1 is 1.2.

In Comparative Example 6, the friction coefficient μ is 0.08, the compressive strength P is 75MPa, and the resistivity ρ is 10×10 ^-6 Ω·m; in Comparative Example 7, the friction coefficient μ is 0.3, the compressive strength P is 150MPa, and the resistivity The rate ρ is 10×10 ^-6 Ω·m; in Comparative Example 8, the friction coefficients μ2 and μ1 of the first and second material layers are 0.4 and 0.08 respectively, μ2/μ1 is 5, and the compressive strengths P2 and P1 are respectively are 260MPa and 75MPa, P2/P1 is 3.75, the resistivity ρ2 and ρ1 are 12 and 10 respectively, and ρ2/ρ1 is 1.2; in Comparative Example 9, the friction coefficients μ2 and μ1 of the first and second material layers are 0.1 respectively. and 0.3, μ2/μ1 is 0.33, the compressive strength P2 and P1 are 75MPa and 225MPa respectively, P2/P1 is 0.33, the resistivity ρ2 and ρ1 are 12 and 10 respectively, and ρ2/ρ1 is 1.2.

It can be seen from Table 1 that the battery obtained by the double-layer negative electrode sheet of the present application (see Examples 1-6) has a shorter charging time and a higher battery capacity. The double-layer pole pieces of Comparative Examples 1-2 and 5-6 were unable to achieve good overall performance, which was mainly reflected in the fact that the battery capacity and charging time could not be balanced, the charging time was too long or the capacity was low. In Comparative Examples 3 and 4, the negative electrode sheet is single-layer coated, and there is a problem of uneven performance: the porosity is low, and the resulting battery capacity is high, but the charging time is too long; the porosity is high, The resulting battery capacity has a shorter charging time but a smaller capacity.

Table 2

Table 2 shows the influence of porosity Q2, Q1 and resistivity μ1, μ2 in the negative electrode sheet on battery performance. Among them, in various embodiments and comparative examples, the particle size D, compressive strength P and resistivity ρ of the material for preparing the negative electrode sheet are respectively:

First material layer: D1 is 18.5μm, P1 is 75MPa, ρ1 is 10×10 ^-6 Ω·m;

Second material layer: D2 is 12.5μm, P2 is 150MPa, ρ2 is 12×10 ^-6 Ω·m;

Furthermore, D2/D1 is 0.68, P2/P1 is 2, and ρ2/ρ1 is 1.2.

It can be seen from Table 2 that when the friction coefficient of the upper and lower negative electrode active materials is further selected, the charging performance and battery capacity of the negative electrode sheet of the present application can be improved.

table 3

Table 3 shows the effects of porosity Q2, Q1 and compressive strength P1, P2 in the negative electrode sheet on battery performance. Among them, in various embodiments and comparative examples, the particle size D, friction coefficient μ and resistivity ρ of the material for preparing the negative electrode sheet are respectively:

First material layer: D1 is 18.5μm, μ1 is 0.27, ρ1 is 10×10 ^-6 Ω·m;

Second material layer: D2 is 12.5μm, μ2 is 0.3, ρ2 is 12×10 ^-6 Ω·m;

Furthermore, D2/D1 is 0.68, μ2/μ1 is 1.1, and ρ2/ρ1 is 1.2.

It can be seen from Table 3 that when the compression coefficient of the negative active material of the upper and lower layers is further selected, the charging performance and battery capacity of the negative electrode sheet of the present application can be improved.

Table 4

Table 4 shows the influence of porosity Q2, Q1 and resistivity ρ1, ρ2 in the negative electrode piece on battery performance. Among them, in various embodiments and comparative examples, the particle size D, friction coefficient μ and compressive strength P of the material for preparing the negative electrode sheet are respectively:

First material layer: D1 is 18.5μm, μ1 is 0.27, P1 is 75MPa;

Second material layer: D2 is 12.5μm, μ2 is 0.3, P2 is 150MPa;

Furthermore, D2/D1 is 0.68, μ2/μ1 is 1.1, and P2/P1 is 2.

It can be seen from Table 4 that when the resistivity of the upper and lower negative electrode active materials is further selected, the charging performance and battery capacity of the negative electrode sheet of the present application can be improved.

table 5

Table 5 shows embodiments including silicon-based negative electrode materials in the first and/or second negative electrode material layers. Among them, in various embodiments and comparative examples, the particle size D, friction coefficient μ, compressive strength P and resistivity ρ of the material for preparing the negative electrode sheet are respectively:

First material layer graphite material: D1 is 18.5μm, μ1 is 0.27, P1 is 75MPa, ρ1 is 10×10 ^-6 Ω·m;

Second material layer graphite material: D2 is 12.5μm, μ2 is 0.3, P2 is 150MPa, ρ2 is 12×10 ^-6 Ω·m;

The Dv50 of the silicon-based negative electrode material is 7um, the pressure resistance P is 140MPa, and the powder resistivity ρ is 20Ω·m.

It can be seen from Table 5 that adding silicon-based negative electrode material to the negative electrode material layer can further improve the comprehensive performance of the negative electrode sheet of the present application and achieve a good balance between battery capacity and charging time.

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

A negative pole piece, which includes:

current collector,

a first negative electrode material layer disposed on at least one surface of the current collector, the first negative electrode material layer including a first negative electrode active material;

a second negative electrode material layer disposed on the first negative electrode material layer, the second negative electrode material layer including a second negative electrode active material;

The first negative electrode material layer has a porosity Q1, the second negative electrode material layer has a porosity Q2, and 1.11≤Q2/Q1≤1.45.
The negative electrode piece according to claim 1, wherein 1.18≤Q2/Q1≤1.45.
The negative electrode sheet according to claim 1 or 2, wherein the porosity Q1 of the first negative electrode material layer is 15% to 35%, optionally 20% to 30%.
The negative electrode plate according to any one of claims 1 to 3, wherein the porosity Q2 of the second negative electrode material layer is 20% to 40%, optionally 25% to 35%.
The negative electrode sheet according to any one of claims 1 to 4, wherein the first negative active material has a median particle diameter of D1, the second negative active material has a median particle diameter of D2, and 0.4 ≤D2/D1≤0.95, optionally 0.6≤D2/D1≤0.8.
The negative electrode sheet according to any one of claims 1 to 5, wherein the friction coefficient of the first negative active material is μ1, the friction coefficient of the second negative active material is μ2, and 1≤μ2/μ1≤ 2, optionally 1.1≤μ2/μ1≤1.7.
The negative electrode piece according to any one of claims 1 to 6, wherein the compressive strength of the first negative active material is P1, the compressive strength of the second negative active material is P2, and 1.1≤P2 /P1≤2.5, optionally 1.1≤P2/P1≤2.0;

The compressive strength is the pressing pressure per unit area when the negative active material is pressed into a compact with a compacted density of 1.7g/ m3 .
The negative electrode plate according to any one of claims 1 to 7, wherein the resistivity of the first negative active material is ρ1, the resistivity of the second negative active material is ρ2, and 1≤ρ2/ρ1 ≤1.5, optionally 1.2≤ρ2/ρ1≤1.4.
The negative electrode sheet according to any one of claims 1 to 8, wherein the first negative active material and the second negative active material are the same or different, and are each independently selected from: carbon-based negative active materials, transition Metal oxides or combinations thereof, or a combination of carbon-based negative active materials and silicon-based negative active materials, or a combination of transition metal oxides and silicon-based negative active materials;

Optionally, the carbon-based negative active material is selected from graphite, soft carbon, hard carbon or a combination thereof;

Optionally, the transition metal oxide is selected from lithium titanate, lithium niobate, lithium ferrite or combinations thereof;

Optionally, the silicon-based negative active material is selected from elemental silicon, silicon-oxygen composite, silicon-carbon composite, silicon-nitride composite, silicon alloy or combinations thereof.
The negative electrode sheet according to claim 9, wherein the second negative electrode material layer includes 0 to 25% by weight, optionally 0 to 10% by weight of silicon-based negative active material, based on the second Total weight of negative active material.
The negative electrode sheet according to claim 9 or 10, wherein the first negative electrode material layer includes 0 to 25% by weight, optionally 0 to 10% by weight of silicon-based negative active material, based on the The total weight of the first negative active material.
A secondary battery including the negative electrode plate according to any one of claims 1 to 11.
A battery module including the secondary battery according to claim 12.
A battery pack comprising the battery module according to claim 13.
An electrical device including at least one selected from the group consisting of the secondary battery of claim 12, the battery module of claim 13, or the battery pack of claim 14.