WO2024092472A1

WO2024092472A1 - Composite negative electrode active material, negative electrode sheet comprising same, electrode assembly, battery cell, battery, and electric device

Info

Publication number: WO2024092472A1
Application number: PCT/CN2022/128817
Authority: WO
Inventors: 白文龙; 武宝珍; 王育文; 游兴艳; 郑蔚; 叶永煌; 金海族; 吴凯
Original assignee: 宁德时代新能源科技股份有限公司
Priority date: 2022-10-31
Filing date: 2022-10-31
Publication date: 2024-05-10
Also published as: CN116888758A

Abstract

Disclosed in the present application are a composite negative electrode active material, a negative electrode sheet comprising same, an electrode assembly, a battery cell, a battery, and an electric device. The composite negative electrode active material comprises: silicon-oxygen complex particles; and high-dielectric-constant material particles, which are attached to the surface of the silicon-oxygen complex particles and have a relative dielectric constant ε of more than or equal to 70.

Description

Composite negative electrode active material, negative electrode sheet containing the same, electrode assembly, battery cell, battery and electrical device

Technical Field

The present application belongs to the technical field of secondary batteries, and specifically relates to a composite negative electrode active material, a negative electrode sheet containing the same, an electrode assembly, a battery cell, a battery and an electrical device.

Background technique

Secondary batteries rely on active ions to be reciprocated between the positive and negative electrodes for charging and discharging. They have outstanding characteristics such as high energy density, long cycle life, no pollution, and no memory effect. Therefore, as a clean energy, secondary batteries have gradually spread from electronic products to large-scale devices such as electric vehicles to adapt to the sustainable development strategy of the environment and energy.

However, during high-rate charging of secondary batteries, lithium deposition will inevitably occur on the surface of the negative electrode. In order to reduce safety hazards, secondary batteries are generally charged at a lower rate, which greatly limits the application of secondary batteries. Therefore, improving the fast charging performance of secondary batteries is an urgent problem to be solved.

Summary of the invention

The purpose of the present application is to provide a composite negative electrode active material, a negative electrode plate containing the same, an electrode assembly, a battery cell, a battery and an electrical device, aiming to improve the fast charging performance of a secondary battery.

In order to achieve the above-mentioned invention objectives, the first aspect of the present application provides a composite negative electrode active material, which includes silicon-oxygen composite particles; and high dielectric constant material particles attached to the surface of the silicon-oxygen composite particles, wherein the relative dielectric constant ε of the high dielectric constant material particles is ≥70.

It is not intended to be limited by any theory or explanation. In the composite negative electrode active material particles of the present application, the high dielectric constant material particles are attached to the surface of the silicon-oxygen composite particles. The dielectric constant of the high dielectric constant material particles is similar to the dielectric constant of the electrolyte, and has a low binding energy with lithium ions, which is conducive to reducing the desolvation barrier, thereby improving the desolvation rate of lithium ions. Therefore, when the composite negative electrode active material of the present application is applied to a secondary battery, the lithium ions enriched on the surface of the negative electrode sheet can be quickly desolvated, adsorbed on the surface of the high dielectric constant material particles, and then quickly enter the interior of the negative electrode sheet through the three-phase interface of the electrolyte-high dielectric constant material-silicon-oxygen composite particles, thereby accelerating the insertion rate of lithium ions. Thus, even when facing a high rate of charging, lithium ions can have a high insertion rate, so that it is not easy to precipitate on the surface of the negative electrode sheet, and then can significantly improve the fast charging performance of the secondary battery.

In addition, since high dielectric constant material particles usually have high hydrophobicity and are easy to settle in the negative electrode slurry, in order to ensure the suspension and uniform dispersion of high dielectric constant material particles, more binders and dispersants need to be used. In the composite negative electrode active material of the present application, the high dielectric constant material particles are attached to the surface of the silicon-oxygen composite particles and are not easy to settle in the negative electrode slurry, so there is no need to increase the amount of binder and dispersant. Therefore, the composite negative electrode active material of the present application is applied to secondary batteries, and the secondary batteries can also maintain high energy density.

In any embodiment of the present application, the high dielectric constant material particles are selected from metal oxoates; optionally, the high dielectric constant material particles are selected from metal oxoates with piezoelectricity, and more optionally, the high dielectric constant material particles are selected from barium titanate, lead titanate, lithium niobate, lead zirconate titanate, lead metaniobate, lead barium lithium niobate or a combination thereof. When the high dielectric constant material particles selected from the above types are affected by the electric field, a reverse electric field will be generated, so that the SEI film formed at the three-phase interface of the electrolyte-high dielectric constant material-silicon oxygen composite particles becomes thinner. Thus, the long-term cycle performance and fast charging performance of the secondary battery can be improved. In particular, when the high dielectric constant material particles are selected from metal oxoates with piezoelectricity, during the charging process, the silicon oxygen composite particles expand in volume, thereby squeezing the piezoelectric material particles. At this time, the metal oxoate can generate a reverse electric field under the extrusion effect, thereby further thinning the SEI film formed at the three-phase interface of the electrolyte-high dielectric constant material-silicon oxygen composite particles. Thus, the long-term cycle performance and fast charging performance of the secondary battery can be further improved.

In any embodiment of the present application, the high dielectric constant material particles are barium titanate, and the X-ray powder diffraction pattern of the composite negative electrode active material particles has characteristic peaks at 2θ located at the following positions: 20°~24°, 29°~33°, 36°~40°, 43°~47°, 54°~58°, and 62°~68°. Barium titanate has low dielectric loss and is not prone to heat failure, so that it can have stable properties during the charge and discharge cycle of the secondary battery. Therefore, the composite negative electrode active material of the present application is applied to the secondary battery, which can enable the secondary battery to have good cycle performance and long-term stable fast charging performance.

In any embodiment of the present application, 80≤ε≤200, optionally, 90≤ε≤100. When the relative dielectric constant of the high dielectric constant material particles is within the above-mentioned suitable range, it is advantageous to match most electrolytes known in the art. Thus, the applicability of the composite negative electrode active material of the present application can be improved, and the application scope of the composite negative electrode active material can be broadened.

In any embodiment of the present application, the volume average particle size Dv50 of the high dielectric constant material particles satisfies: 50nm≤Dv50≤100nm. Optionally, 50nm≤Dv50≤80nm. When the Dv50 of the high dielectric constant material is within the above-mentioned smaller range, it is beneficial for the high dielectric constant material particles to adhere tightly to the surface of the silicon-oxygen composite particles, thereby facilitating the improvement of the compaction density of the negative electrode film layer using the composite negative electrode material. In addition, since the Dv50 of the high dielectric constant material is small and the space occupied is very small, the negative electrode film layer can maintain a high porosity. As a result, the negative electrode film layer can have good electrolyte wetting properties, which is beneficial to improving the dynamic properties of the negative electrode plate, and further to improving the fast charging performance of the secondary battery.

In any embodiment of the present application, the mass ratio of the high dielectric constant material particles to the silicon-oxygen composite particles is 0.5:100 to 5:100, and can be optionally 0.5:100 to 1.5:100. When the mass ratio of the high dielectric constant material particles to the silicon-oxygen composite particles is within the above-mentioned appropriate range, on the one hand, the high dielectric constant material particles can fully play the role of reducing the desolvation barrier of lithium ions, thereby increasing the insertion rate of lithium ions in the negative electrode; on the other hand, the content of the high dielectric constant material particles is appropriate, which is conducive to the composite negative electrode active material having a high theoretical gram capacity. As a result, the secondary battery using the composite negative electrode active material of the present application can have both excellent fast charging performance and high energy density.

In any embodiment of the present application, the silicon-oxygen composite particles are bonded to the high dielectric constant material particles through the covalent bonds formed after the reaction of _-NH2 and epoxy groups, so that the high dielectric constant material particles are attached to the surface of the silicon-oxygen composite particles. When the silicon-oxygen composite particles are bonded to the high dielectric constant material particles through the covalent bonds formed after the reaction of _-NH2 and epoxy groups, the high dielectric constant material particles can be more firmly attached to the surface of the silicon-oxygen composite particles. Thus, in the process of preparing the negative electrode slurry, the composite negative electrode active material can be evenly dispersed in the solvent and is not prone to sedimentation. Therefore, the composite negative electrode active material of the present application is applied to secondary batteries, which can enable the secondary batteries to have both good fast charging performance and high energy density.

In any embodiment of the present application, the infrared absorption spectrum of the composite negative electrode active material has characteristic peaks located at the following positions: 3330cm ^-1 ~3370cm ^-1 , 1180cm ^-1 ~1220cm ^-1 , and 1080cm ^-1 ~1120cm ^-1 . When the infrared absorption spectrum of the composite negative electrode active material has the above-mentioned characteristic peaks, the silicon-oxygen composite particles and the high dielectric constant material particles can be combined through the covalent bonds formed after the reaction of _-NH2 and epoxy groups, so that the high dielectric constant material particles are more firmly attached to the surface of the silicon-oxygen composite particles. Thus, in the process of preparing the negative electrode slurry, the composite negative electrode active material can be evenly dispersed in the solvent and is not prone to sedimentation. Therefore, the composite negative electrode active material of the present application is applied to secondary batteries, which can enable the secondary batteries to have both good fast charging performance and high energy density.

A second aspect of the present application provides a negative electrode plate, which includes a negative electrode current collector; and a negative electrode film layer located on at least one side of the negative electrode current collector, wherein the negative electrode film layer includes the composite negative electrode active material of the first aspect of the present application.

Without intending to be limited by any theory or explanation, the negative electrode film layer of the negative electrode plate of the present application contains composite negative electrode active material particles, so that during the charging process, the lithium ions enriched on the surface of the negative electrode plate can be quickly desolvated and adsorbed on the surface of the high dielectric constant material particles of the composite negative electrode active material, and then quickly enter the interior of the negative electrode plate through the three-phase interface of the electrolyte-high dielectric constant material-silicon oxygen composite particles, thereby accelerating the insertion rate of lithium ions. Even when facing high-rate charging, lithium ions can have a high insertion rate, so it is not easy to precipitate on the surface of the negative electrode plate, thereby significantly improving the fast charging performance of the secondary battery.

In any embodiment of the present application, the negative electrode film layer further comprises a second negative electrode active material, and the second negative electrode active material is selected from one or more of a carbon-based negative electrode active material, a silicon-based negative electrode active material or a tin-based negative electrode active material.

Optionally, the mass ratio of the composite negative electrode active material to the second negative electrode active material is 1:96 to 1:2.88.

The negative electrode film layer also contains the above-mentioned second negative electrode active material particles, which is conducive to adjusting the compaction density, porosity and other parameters of the negative electrode film layer, thereby facilitating the capacity of the negative electrode active material in the negative electrode film layer. Therefore, it is conducive to improving the energy density and cycle performance of the secondary battery.

In any embodiment of the present application, the second negative electrode active material is selected from pre-lithiated silicon oxide particles.

Optionally, the pre-lithiated silicon oxide includes: a silicon oxide core; a lithium silicate layer, located on the surface of the silicon oxide core, which includes lithium silicate grains, and silicon nanocrystals and/or silicon dioxide nanocrystals dispersed in the lithium silicate; and a carbon coating layer, coated on at least part of the surface of the lithium silicate layer. When the second negative electrode active material is selected from pre-lithiated silicon oxide particles, the negative electrode plate can be pre-supplemented with lithium, thereby improving the first coulombic efficiency of the secondary battery. In particular, when the pre-lithiated silicon oxide includes the above-mentioned silicon oxide core, lithium silicate layer and carbon coating layer, the second negative electrode active material can have a low volume expansion rate, thereby reducing the irreversible capacity loss of the second negative electrode material and the volume expansion of the secondary battery, thereby improving the cycle stability of the secondary battery.

In any embodiment of the present application, based on the total mass of the lithium silicate grains, the silicon nano-grains and the silicon dioxide, the mass percentage of the lithium silicate grains is 10% to 25%.

Optionally, the thickness d ₁ of the lithium silicate layer satisfies: d ₁ ≤35 nm, optionally, 15 nm≤d ₁ ≤35 nm.

Optionally, the thickness d ₂ of the carbon coating layer satisfies: d ₂ ≤ 25 nm, optionally, 15 nm ≤ _{d 2} ≤ 25 nm.

When the pre-lithiated silicon oxide particles meet the above conditions, the second negative electrode active material can have a lower volume expansion rate, thereby further reducing the irreversible capacity loss of the second negative electrode material and the volume expansion of the secondary battery, thereby improving the cycle stability of the secondary battery.

A third aspect of the present application provides an electrode assembly, which includes the negative electrode plate of the second aspect of the present application.

The electrode assembly of the present application includes the negative electrode plate of the second aspect of the present application, and is applied to a secondary battery, so that the secondary battery can have good fast charging performance.

A fourth aspect of the present application provides a battery cell, comprising a housing and the electrode assembly of the third aspect of the present application, wherein the electrode assembly is accommodated in the housing.

The battery cell of the present application includes the electrode assembly of the third aspect of the present application, and thus can have good fast charging performance.

A fifth aspect of the present application provides a battery, which includes a plurality of battery cells according to the fourth aspect of the present application.

A sixth aspect of the present application provides an electrical device, which includes the battery cell of the fourth aspect of the present application, and the battery cell is used to provide electrical energy.

The battery and the electric device of the present application include the battery cell provided by the present application, and thus have at least the same advantages as the battery cell.

BRIEF DESCRIPTION OF THE DRAWINGS

In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings required for use in the embodiments of the present application will be briefly introduced below. Obviously, the drawings described below are only some implementation methods of the present application. For ordinary technicians in this field, other drawings can be obtained based on the drawings without creative work.

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

FIG. 2 is an exploded schematic diagram of the embodiment of the battery cell shown in FIG. 1 .

FIG. 3 is a schematic diagram of an embodiment of a battery module of the present application.

FIG. 4 is a schematic diagram of an embodiment of a battery pack of the present application.

FIG. 5 is an exploded view of the battery pack of the present application shown in FIG. 4 .

FIG. 6 is a schematic diagram of an electric device using the secondary battery of the present application as a power source.

FIG. 7 is a SOC-rate statistical diagram of the secondary batteries of Example 1 and Comparative Example 2 of the present application.

FIG. 8 is an XRD diagram of the composite negative electrode active material of Example 2 of the present application.

FIG. 9 is an infrared absorption spectrum of the composite negative electrode active material of Example 2 of the present application.

Description of reference numerals:

1 battery pack; 2 upper box; 3 lower box; 4 battery module; 5 battery cell; 51 shell; 52 electrode assembly; 53 cover plate.

Detailed ways

In order to make the invention purpose, technical scheme and beneficial technical effect of the present application clearer, the present application is further described in detail in conjunction with the embodiments below. It should be understood that the embodiments described in this specification are only for explaining the present application, not for limiting the present application.

For simplicity, only some numerical ranges are explicitly disclosed herein. However, any lower limit can be combined with any upper limit to form an unambiguous range; and any lower limit can be combined with other lower limits to form an unambiguous range, and any upper limit can be combined with any other upper limit to form an unambiguous range. In addition, although not explicitly stated, each point or single value between the range endpoints is included in the range. Thus, each point or single value can be combined with any other point or single value as its own lower limit or upper limit or with other lower limits or upper limits to form an unambiguous range.

In the description of this article, it should be noted that, unless otherwise specified, "above" and "below" are inclusive of the number itself, and "several" in "one or several" means two or more.

In the description herein, unless otherwise specified, the term "or" is inclusive. For example, the phrase "A or B" means "A, B, or both A and B". More specifically, any of the following conditions satisfies the condition "A or B": 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).

It should be understood that relational terms such as “first”, “second”, etc. are merely used to distinguish one entity or operation from another entity or operation, but do not necessarily require or imply any actual relationship or order between these entities or operations.

The above invention summary of the present application is not intended to describe each disclosed embodiment or each implementation in the present application. The following description more specifically illustrates exemplary embodiments. In many places throughout the application, guidance is provided by a series of examples, which can be used in various combinations. In each example, enumeration is only used as a representative group and should not be interpreted as exhaustive.

During the charging process of lithium-ion batteries, lithium ions are extracted from the positive electrode and embedded in the negative electrode. During the embedding process, the difference in the desolvation rate of solvated lithium ions at the SEI membrane interface will lead to uneven distribution of lithium ion concentration. Lithium ions are easily enriched at the interface between the SEI membrane and the negative electrode plate, resulting in excessive lithium ion concentration on the local surface of the negative electrode plate. When facing high-rate charging, when lithium ions do not have time to embed into the negative electrode, they will combine with electrons and precipitate on the surface of the negative electrode plate in the form of lithium metal. This is the lithium precipitation phenomenon. Since the conductivity of lithium metal is much higher than that of the negative electrode plate, other lithium ions will preferentially deposit on the surface of lithium metal, causing the volume of lithium metal to grow and even form lithium dendrites. Lithium metal or lithium dendrites may bypass the separator and form a micro-short circuit with the positive electrode, causing problems such as self-discharge and leakage current. In severe cases, they may even pierce the separator and cause a battery short circuit.

In the related art, the positive and negative electrode capacity ratio is designed to improve the negative electrode capacity to alleviate the lithium plating problem under high-rate charging. However, this method will cause a waste of negative electrode capacity.

After in-depth thinking, the inventors found that the desolvation rate of lithium ions is one of the important factors affecting the embedding rate of lithium ions in the negative electrode. After research, the inventors found that when the dielectric constant of the surface of the negative electrode plate is close to the dielectric constant of the electrolyte, the binding energy between the surface of the negative electrode plate and the lithium ions is low, and the solvated lithium ions will quickly desolvate and be adsorbed by the surface of the negative electrode plate, thereby entering the interior of the negative electrode plate. However, the dielectric constant of existing negative electrode active materials is small, and it is quite different from the dielectric constant of the electrolyte, making it difficult to accelerate the desolvation rate of lithium ions.

After further research, the inventors found that when the negative electrode film layer contains a high dielectric constant material, during the charging process, since the dielectric constant of the high dielectric constant material is similar to that of the electrolyte, its binding energy with lithium ions is lower than that of the negative electrode active material. As a result, the solvated lithium ions will quickly desolvate and be adsorbed on the surface of the high dielectric constant material, and then quickly enter the interior of the negative electrode plate through the three-phase interface of the electrolyte-high dielectric constant material-negative electrode active material, thereby accelerating the insertion rate of lithium ions and improving the fast charging capability of the secondary battery.

In view of this, the inventors, after in-depth research and extensive experiments, provide a composite negative electrode active material, a negative electrode sheet containing the same, an electrode assembly, a battery cell, a battery and an electrical device.

Composite negative electrode active materials

The first aspect of the present application provides a composite negative electrode active material, which includes: silicon-oxygen composite particles; and high dielectric constant material particles attached to the surface of the silicon-oxygen composite particles, wherein the relative dielectric constant of the high dielectric constant material particles is ε≥70, for example, ε≥70, ε≥80, ε≥90, ε≥100, ε≥200 or ε≥300, etc.

The silicon-oxygen composite particles may include particles formed by silicon-oxygen composites known in the art, and the present application does not limit the specific type of silicon-oxygen composites. As an example, the silicon-oxygen composite may include but is not limited to SiO _x (0<x<2) or pre-lithiated SiO _x (0<x<2).

The high dielectric constant material particles may include material particles with a relative dielectric constant ε≥70 known in the art, and the specific type thereof may be selected according to the dielectric constant of the electrolyte and is not limited here.

The high dielectric constant material particles can be attached to the surface of the silicon-oxygen composite particles by covalent bonds or the action of a binder. Those skilled in the art can modify the high dielectric constant material particles and/or the silicon-oxygen composite particles so that the high dielectric constant material particles and the silicon-oxygen composite particles are connected by covalent bonds, or can select a suitable binder so that the high dielectric constant material particles are attached to the surface of the silicon-oxygen composite particles, which is not limited here. As an example, the binder can include but is not limited to styrene-butadiene rubber (SBR), an amphoteric polymer binder, or a combination thereof.

The present application does not limit the number of high dielectric constant material particles attached to the surface of a single silicon-oxygen composite particle, which may be one or more. In some embodiments, the number of high dielectric constant material particles on the surface of a single silicon-oxygen composite particle is multiple, and multiple high dielectric constant materials can form a structure similar to a coating layer on the surface of the silicon-oxygen composite particle, thereby inhibiting the side reaction between the silicon-oxygen composite and the electrolyte, thereby improving the cycle performance of the secondary battery.

Although the mechanism is not yet clear, the inventors unexpectedly discovered that the composite negative electrode active material of the present application can be applied to secondary batteries to significantly improve the fast charging capability of the secondary batteries.

In some embodiments, the high dielectric constant material particles may be selected from metal oxoates. Alternatively, the high dielectric constant material particles may be selected from metal oxoates having piezoelectricity. More preferably, the high dielectric constant material particles may be selected from barium titanate, lead titanate, lithium niobate, lead zirconate titanate, lead metaniobate, lead barium lithium niobate or a combination thereof.

In the present application, metal oxoate may refer to a salt containing metal oxoate. In the present application, piezoelectricity has a well-known meaning in the art, which may refer to the property of a single crystal of a certain medium, when subjected to directional pressure or tension, that the two sides of the crystal perpendicular to the stress have equal amounts of opposite charges on their surfaces.

It is not intended to be limited to any theory or explanation. When the high dielectric constant material particles selected from the above-mentioned types are affected by the electric field, a reverse electric field will be generated, which inhibits the formation of the surrounding SEI film, so that the SEI film formed at the three-phase interface of the electrolyte-high dielectric constant material-silicon oxygen composite particles is thinned. Thus, not only can the loss of active lithium ions and the consumption of electrolyte be reduced, but also the migration path of lithium ions in the SEI film can be shortened, so that the long-term cycle performance and fast charging performance of the secondary battery can be improved. In particular, when the high dielectric constant material particles are selected from metal oxoates with piezoelectricity, during the charging process, the silicon oxygen composite particles produce volume expansion, thereby squeezing the piezoelectric material particles. At this time, the metal oxoate can generate a reverse electric field under the extrusion effect, so that the SEI film formed at the three-phase interface of the electrolyte-high dielectric constant material-silicon oxygen composite particles is further thinned. Thus, the long-term cycle performance and fast charging performance of the secondary battery can be further improved.

In some embodiments, the high dielectric constant material particles may be barium titanate (BTO), and the X-ray powder diffraction (XRD) pattern of the composite negative electrode active material particles may have characteristic peaks at 2θ located at the following positions: 20°~24°, 29°~33°, 36°~40°, 43°~47°, 54°~58°, and 62°~68°.

Without intending to be bound by any theory or explanation, the inventors have found that barium titanate has low dielectric loss and is not prone to heat failure, so that it can have stable properties during the charge and discharge cycle of the secondary battery. Therefore, the composite negative electrode active material of the present application is applied to the secondary battery, which can make the secondary battery have good cycle performance and long-term stable fast charging performance.

In some embodiments, the composite negative electrode active material may satisfy: 80≤ε≤200, for example, ε may be 80, 100, 120, 150, 180, 200, or within the range of any of the above values. Alternatively, 90≤ε≤100, ε may be 90, 92, 95, 98, 100, or within the range of any of the above values.

Without intending to be limited by any theory or explanation, when the relative dielectric constant of the high dielectric constant material particles in the composite negative electrode active material is within the above-mentioned suitable range, it is advantageous to match with most electrolytes known in the art. Thus, the applicability of the composite negative electrode active material of the present application can be improved and the application scope of the composite negative electrode active material can be broadened.

In some embodiments, the volume average particle size Dv50 of the high dielectric constant material particles may satisfy: 50nm≤Dv50≤100nm, for example, Dv50 may be 100nm, 90nm, 80nm, 70nm, 60nm, 50nm, or within the range of any of the above values. Optionally, 50nm≤Dv50≤80nm, for example, Dv50 may be 80nm, 70nm, 60nm, 50nm, or within the range of any of the above values.

Without intending to be limited by any theory or explanation, when the Dv50 of the high dielectric constant material is within the above-mentioned smaller range, it is beneficial for the high dielectric constant material particles to be closely attached to the surface of the silicon-oxygen composite particles. The high dielectric constant material particles are closely attached to the surface of the silicon-oxygen composite particles, which is beneficial to reduce the gap between the high dielectric constant material and the silicon-oxygen composite, thereby facilitating the improvement of the compaction density of the negative electrode film layer using the composite negative electrode material. In addition, since the Dv50 of the high dielectric constant material is small, the space occupied is very small, so that the negative electrode film layer can maintain a high porosity. As a result, the negative electrode film layer can have good electrolyte infiltration performance, which is beneficial to improve the dynamic performance of the negative electrode plate, and then to improve the fast charging performance of the secondary battery.

In some embodiments, the mass ratio of the high dielectric constant material particles to the silicon-oxygen composite particles may be 0.5:100 to 5:100, for example, 0.5:100, 1:100, 1.5:100, 2:100, 3.5:100, 3:100, 3.5:100, 4:100, 4.5:100, 5:100, or within the range of any of the above ratios. Optionally, the mass ratio of the high dielectric constant material particles to the silicon-oxygen composite particles may be 0.5:100 to 1.5:100, for example, 0.5:100, 0.8:100, 1:100, 1.2:100, 1.5:100, or within the range of any of the above ratios.

Without intending to be limited by any theory or explanation, when the mass ratio of high dielectric constant material particles to silicon-oxygen composite particles is within the above-mentioned suitable range, on the one hand, the high dielectric constant material particles can fully play the role of reducing the lithium ion desolvation barrier, thereby increasing the insertion rate of lithium ions in the negative electrode; on the other hand, the content of high dielectric constant material particles is appropriate, which is conducive to the composite negative electrode active material having a high theoretical gram capacity. Therefore, the secondary battery using the composite negative electrode active material of the present application can have both excellent fast charging performance and high energy density.

In some embodiments, the silicon-oxygen composite particles are bonded to the high dielectric constant material particles through covalent bonds formed by the reaction of -NH ₂ and epoxy groups, so that the high dielectric constant material particles are attached to the surface of the silicon-oxygen composite particles.

The covalent bond formed by the reaction of _-NH2 with the epoxy group has a well-known meaning in the art, and can be represented by: As an example, the covalent bond can represent a covalent bond contained in the structure -NH- _CH2 -CH(OH)-, or a covalent bond contained in a substituted structure -NH- _CH2 -CH(OH)-.

It is not intended to be limited by any theory or explanation. When the silicon-oxygen composite particles are bonded to the high dielectric constant material particles through the covalent bond formed by the reaction of _-NH2 and epoxy groups, the high dielectric constant material particles can be more firmly attached to the surface of the silicon-oxygen composite particles. Thus, in the process of preparing the negative electrode slurry, the composite negative electrode active material can be evenly dispersed in the solvent and is not prone to sedimentation. Therefore, the composite negative electrode active material of the present application is applied to a secondary battery, which can enable the secondary battery to have both good fast charging performance and high energy density.

In some embodiments, the infrared absorption spectrum of the composite negative electrode active material has characteristic peaks located at the following positions: 3330 cm ^-1 to 3370 cm ^-1 , 1180 cm ^-1 to 1220 cm ^-1 , and 1080 cm ^-1 to 1120 cm ^-1 .

The above-mentioned characteristic peak at 3330cm ^-1 ~3370cm ^-1 can be a characteristic peak characterizing the -NH- bond, the characteristic peak at 1180cm ^-1 ~1220cm ^-1 can be a characteristic peak characterizing the Si-C bond, and the characteristic peak at 1080cm ^-1 ~1120cm ^-1 can be a characteristic peak characterizing the Si-O bond. In this embodiment, the silicon-oxygen composite particles can be silicon-oxygen composite particles modified by a silane coupling agent containing an epoxy group, and the high dielectric constant material particles can be high dielectric constant material particles modified by an amino-containing silane coupling agent. Thus, the silicon-oxygen composite particles and the high dielectric constant material particles can be combined by covalent bonds formed after the reaction of _-NH2 and epoxy groups, so that the high dielectric constant material particles are more firmly attached to the surface of the silicon-oxygen composite particles. Thus, in the process of preparing the negative electrode slurry, the composite negative electrode active material can be evenly dispersed in the solvent and is not prone to sedimentation. Therefore, the composite negative electrode active material of the present application is applied to secondary batteries, which can enable the secondary batteries to have both good fast charging performance and high energy density.

In the present application, relative dielectric constant has a meaning known in the art and can be measured by methods and instruments known in the art, for example, by referring to the test standard GB1409-88.

In the present application, the XRD pattern can be measured by methods and instruments known in the art. For example, it can be obtained by XRD testing using a Bruker D8 ADVANCE X-ray powder diffractometer, wherein the radiation source of the XRD test is a Cu Kα target, and the test parameters can be set to: tube voltage of 40 kV, tube current of 40 mA, scanning step of 0.00836°, scanning time of each scanning step of 0.3 s, and 2θ range of 5° to 80°.

In this application, the volume average particle size Dv50 of high dielectric constant material particles has a well-known meaning in the art and can be measured by methods and instruments known in the art. Wherein, Dv50 means that in the volume-based particle size distribution, 50% of the particles have a particle size smaller than this value. The volume average particle size Dv50 of high dielectric constant material particles can be measured with reference to GB/T 19077-2016 particle size distribution laser diffraction method using a laser particle size analyzer (e.g., Malvern Mastersizer 2000E, UK).

In the present application, the infrared absorption spectrum can be measured by methods and instruments known in the art. For example, it can be obtained by using an infrared spectrometer. Specifically, the composite negative electrode active material can be soaked in NMP, centrifuged and filtered, and the filtered clear liquid is heated and evaporated to ≤5mL. The infrared absorption spectrum of the composite negative electrode material can be obtained by testing with reference to the test method of GB/T 21186-2007.

In the present application, the composite negative electrode active material can be obtained in a variety of ways. In some embodiments, the composite negative electrode active material can be obtained by self-production. For example, it can be prepared by referring to the more classical covalent grafting chemical reaction. As an example, the composite negative electrode active material can be prepared by the following steps:

placing hydroxyl-functionalized high dielectric constant material particles in an ethanol solution of γ-aminopropyltriethoxysilane, and soaking them at 60° C. to 80° C. for 6 h to 8 h to obtain high dielectric constant material particles having amino functional groups on the surface;

The silicon-oxygen composite particles are placed in an ethanol solution of γ-glycidyloxypropyltrimethoxysilane, stirred for a period of time, for example, 6 hours to 8 hours, and then centrifuged, washed, and dried to obtain silicon-oxygen composite particles having epoxy functional groups on the surface;

The high dielectric constant material particles containing amino functional groups on the surface and the silicon-oxygen composite particles containing epoxy functional groups on the surface are placed in a solvent (such as ethanol) and kept at 60°C to 80°C for 6h to 8h to allow the amino functional groups to fully react with the epoxy functional groups, thereby obtaining the composite negative electrode material of the present application.

It should be noted that the above example is only one of the methods for obtaining the negative electrode active material of the present application, and is only used to explain the present application, rather than to limit the present application.

Negative electrode

The second aspect of the present application provides a negative electrode sheet, comprising a negative electrode current collector and a negative electrode film layer located on at least one side of the negative electrode current collector, wherein the negative electrode film layer comprises the composite negative electrode active material of the present application.

In some embodiments, the negative electrode film layer may further include a second negative electrode active material, and the second negative electrode active material may be selected from one or more of a carbon-based negative electrode active material, a silicon-based negative electrode active material, or a tin-based negative electrode active material.

Optionally, the mass ratio of the composite negative electrode active material to the second negative electrode active material may be 1:96 to 1:2.88.

Without intending to be bound by any theory or explanation, the negative electrode film layer also contains the above-mentioned second negative electrode active material particles, which is conducive to adjusting the compaction density, porosity and other parameters of the negative electrode film layer, thereby facilitating the capacity of the negative electrode active material in the negative electrode film layer. Therefore, it is conducive to improving the energy density and cycle performance of the secondary battery.

In some embodiments, the second negative electrode active material may be selected from pre-lithiated silicon oxide particles.

Optionally, the pre-lithiated silicon oxide may include: a silicon oxide core; a lithium silicate layer located on the surface of the silicon oxide core, which includes lithium silicate grains, and silicon nanocrystals and/or silicon dioxide nanocrystals dispersed in the lithium silicate; and a carbon coating layer coated on at least a portion of the surface of the lithium silicate layer.

Without intending to be limited by any theory or explanation, when the second negative electrode active material is selected from pre-lithiated silicon oxide particles, the negative electrode plate can be pre-replenished with lithium, thereby improving the first coulombic efficiency of the secondary battery. In particular, when the pre-lithiated silicon oxide includes the above-mentioned silicon oxide core, lithium silicate layer and carbon coating layer, the second negative electrode active material can have a low volume expansion rate, thereby reducing the irreversible capacity loss of the second negative electrode material and the volume expansion of the secondary battery, thereby improving the cycle stability of the secondary battery.

In some embodiments, based on the total mass of the lithium silicate grains, the silicon nano-crystals and the silicon dioxide, the mass percentage of the lithium silicate grains may be 10% to 25%.

Optionally, the thickness _d1 of the lithium silicate layer may satisfy: _d1≤35nm , optionally, _{15nm≤d1≤35nm} .

Optionally, the thickness d ₂ of the carbon coating layer may satisfy: d ₂ ≤ 25 nm, optionally, 15 nm ≤ _{d 2} ≤ 25 nm.

In the present application, the pre-lithiated silicon oxide particles that meet the above conditions can be obtained by selecting the pre-lithiated silicon oxide particles, or by adjusting the preparation process of the pre-lithiated silicon oxide particles. As an example, the pre-lithiated silicon oxide particles can be selected by X-ray photoelectron spectroscopy (XPS) to obtain pre-lithiated silicon oxide particles that meet the above conditions. It is not intended to be limited to any theory or explanation. When the pre-lithiated silicon oxide particles meet the above conditions, the second negative electrode active material can have a lower volume expansion rate, thereby further reducing the irreversible capacity loss of the second negative electrode material and the volume expansion of the secondary battery, thereby improving the cycle stability of the secondary battery.

The present application does not limit the negative electrode current collector, and the negative electrode current collector may be a metal foil or a composite current collector (a metal material may be disposed on a polymer substrate to form a composite current collector). For example, copper foil may be used as the metal foil. 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 substrate. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

In the negative electrode sheet of the present application, the negative electrode film layer can be arranged on one side of the negative electrode current collector, or can be arranged on both sides of the negative electrode current collector at the same time. For example, the negative electrode current collector has two opposite sides in its own thickness direction, and the negative electrode film layer is arranged on any one side or both sides of the two opposite sides of the negative electrode current collector.

In some embodiments, the first negative electrode layer and the second negative electrode layer may further optionally include a binder. The binder may be selected from at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA) and carboxymethyl chitosan (CMCS).

In some embodiments, the negative electrode film layer may further include a conductive agent, which may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene and carbon nanofibers.

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

In some embodiments, the negative electrode sheet can be prepared in the following manner: the components for preparing the negative electrode film layer, such as the composite negative electrode active material, the conductive agent, the binder and any other components are dispersed in a solvent (such as deionized water) to form a negative electrode slurry; the negative electrode slurry is coated on one or both surfaces of the negative electrode collector; after drying, cold pressing and other processes, the negative electrode sheet of the present application can be obtained.

It should be noted that the negative electrode film parameters (such as film thickness, compaction density, etc.) given in this application refer to the parameter range of the single-side film. When the negative electrode film is arranged on both sides of the negative electrode current collector, the film parameters on either side meet the requirements of this application and are considered to fall within the protection scope of this application. The ranges of film thickness, compaction density, etc. described in this application refer to the film parameters after cold pressing and used to assemble the battery.

In addition, the negative electrode plate of the present application does not exclude other additional functional layers in addition to the negative electrode film layer. For example, in some embodiments, the negative electrode plate described in the present application may also include a conductive primer layer (e.g., composed of a conductive agent and a binder) disposed between the negative electrode current collector and the negative electrode film layer. In other embodiments, the negative electrode plate described in the present application also includes a protective layer covering the surface of the negative electrode film layer.

Electrode assembly

The third aspect of the present application provides an electrode assembly. Generally, the electrode assembly includes a positive electrode sheet, a negative electrode sheet, and a separator. In some embodiments, the positive electrode sheet, the negative electrode sheet, and the separator can be made into an electrode assembly by a winding process or a lamination process.

[Negative electrode]

The negative electrode sheet of the electrode assembly of the present application includes the negative electrode sheet of the second aspect of the present application. The embodiments of the negative electrode sheet have been described and illustrated in detail above, and will not be repeated here. It can be understood that the electrode assembly of the present application can achieve the beneficial effects of any of the above embodiments of the negative electrode sheet of the present application.

[Positive electrode]

In the electrode assembly of the present application, 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 and including a positive electrode active material. For example, the positive electrode current collector has two surfaces opposite to each other in its thickness direction, and the positive electrode film layer is disposed on any one or both of the two opposite surfaces of the positive electrode current collector.

In the electrode assembly of the present application, the positive electrode active material may adopt the positive electrode active material for electrode assembly known in the art. For example, the positive electrode active material may include one or more of lithium transition metal oxides, lithium phosphates containing olivine structures, and their respective modified compounds. Examples of lithium transition metal oxides may include, but are not limited to, one or more of lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, and their modified compounds. Examples of lithium phosphates containing olivine structures may include, but are not limited to, one or more of lithium iron phosphate, a composite material of lithium iron phosphate and carbon, lithium manganese phosphate, a composite material of lithium manganese phosphate and carbon, lithium iron manganese phosphate, a composite material of lithium iron manganese phosphate and carbon, and their respective modified compounds. The present application is not limited to these materials, and other conventionally known materials that can be used as positive electrode active materials in electrode assemblies may also be used.

In the electrode assembly of the present application, the positive electrode film layer generally comprises a positive electrode active material and an optional binder and an optional conductive agent, and is generally formed by coating a positive electrode slurry, drying, and cold pressing. The positive electrode slurry is generally formed by dispersing the positive electrode active material and the optional conductive agent and binder in a solvent and stirring them uniformly. The solvent may be N-methylpyrrolidone (NMP).

As an example, the binder for the positive electrode film layer may include one or more of polyvinylidene fluoride (PVDF) and polytetrafluoroethylene (PTFE).

As an example, the conductive agent used for the positive electrode film layer may include one or more of superconducting carbon, carbon black (eg, acetylene black, Ketjen black), carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

In the electrode assembly of the present application, the positive electrode current collector may be a metal foil or a composite current collector (a metal material may be disposed on a polymer substrate to form a composite current collector). As an example, the positive electrode current collector may be an aluminum foil.

[Electrolytes]

The electrode assembly of the present application has no specific restrictions on the type of electrolyte, which can be selected according to needs. For example, the electrolyte can be selected from at least one of a solid electrolyte and a liquid electrolyte (ie, an electrolyte solution).

In some embodiments, the electrolyte is an electrolyte solution, which includes an electrolyte salt and a solvent.

In some embodiments, the electrolyte salt may be selected from one or more of LiPF ₆ (lithium hexafluorophosphate), LiBF ₄ (lithium tetrafluoroborate), LiClO ₄ (lithium perchlorate), LiAsF ₆ (lithium hexafluoroarsenate), LiFSI (lithium bisfluorosulfonyl imide), LiTFSI (lithium bistrifluoromethanesulfonyl imide), LiTFS (lithium trifluoromethanesulfonate), LiDFOB (lithium difluorooxalatoborate), LiBOB (lithium dioxalatoborate), LiPO ₂ F ₂ (lithium difluorophosphate), LiDFOP (lithium difluorobisoxalatophosphate) and LiTFOP (lithium tetrafluorooxalatophosphate).

In some embodiments, the solvent can be selected from one or more of ethylene carbonate (EC), propylene carbonate (PC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), butylene carbonate (BC), fluoroethylene carbonate (FEC), methyl formate (MF), methyl acetate (MA), ethyl acetate (EA), propyl acetate (PA), methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), methyl butyrate (MB), ethyl butyrate (EB), 1,4-butyrolactone (GBL), sulfolane (SF), dimethyl sulfone (MSM), ethyl methyl sulfone (EMS) and diethyl sulfone (ESE).

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

[Isolation film]

The isolation membrane is arranged between the positive electrode plate and the negative electrode plate to play an isolating role. The present application has no particular restrictions on the type of isolation membrane, and any known porous structure isolation membrane with good chemical stability and mechanical stability can be selected. In some embodiments, the material of the isolation membrane can be selected from one or more of glass fiber, non-woven fabric, polyethylene, polypropylene and polyvinylidene fluoride. The isolation membrane can be a single-layer film or a multi-layer composite film. When the isolation membrane is a multi-layer composite film, the materials of each layer are the same or different.

Battery Cell

A fourth aspect of the present application provides a battery cell, which includes a housing and the electrode assembly of the first aspect of the embodiment of the present application.

Generally speaking, a battery cell also includes an electrolyte, which plays a role in conducting active ions between the positive electrode and the negative electrode. The present application does not specifically limit the type of electrolyte, and it can be selected according to needs. For example, the electrolyte can be selected from at least one of a solid electrolyte and a liquid electrolyte (i.e., an electrolyte).

The type of electrolyte salt is not specifically limited and can be selected according to actual needs. For example, the electrolyte salt includes one or more selected from lithium salts for lithium ion batteries and sodium salts for sodium ion batteries. As an example, the lithium salt includes one or more selected from lithium hexafluorophosphate (LiPF ₆ ), lithium tetrafluoroborate (LiBF ₄ ), lithium perchlorate (LiClO ₄ ), lithium hexafluoroarsenate (LiAsF ₆ ), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium trifluoromethanesulfonate (LiTFS), lithium difluorooxalatoborate (LiDFOB), lithium dioxalatoborate (LiBOB), lithium difluorophosphate (LiPO ₂ F ₂ ), lithium difluorobis(oxalatophosphate) (LiDFOP), lithium tetrafluorooxalatophosphate (LiTFOP).

The type of solvent is not specifically limited and can be selected according to actual needs. In some embodiments, as an example, the solvent may include one or more selected from ethylene carbonate (EC), propylene carbonate (PC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), butylene carbonate (BC), fluoroethylene carbonate (FEC), methyl formate (MF), methyl acetate (MA), ethyl acetate (EA), propyl acetate (PA), methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), methyl butyrate (MB), ethyl butyrate (EB), 1,4-butyrolactone (GBL), cyclopentane (SF), dimethyl sulfone (MSM), methyl ethyl sulfone (EMS) and diethyl sulfone (ESE).

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

In some embodiments, the housing of a battery cell may be used to encapsulate the electrode assembly and the electrolyte.

In some embodiments, the outer shell of the battery cell may be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc. The outer shell of the battery cell may also be a soft package, such as a bag-type soft package. The material of the soft package may be plastic, such as one or more of polypropylene (PP), polybutylene terephthalate (PBT), polybutylene succinate (PBS), etc.

The present application has no particular limitation on the shape of the battery cell, which may be a flat body, a rectangular parallelepiped or other shapes. FIG1 is a battery cell 5 of a rectangular parallelepiped structure as an example.

FIG2 is a schematic diagram of an exploded view of the battery cell shown in FIG1 . In some embodiments, as shown in FIG2 , the housing may include a shell 51 and a cover plate 53. Among them, the shell 51 may include a bottom plate and a side plate connected to the bottom plate, and the bottom plate and the side plate together form a receiving cavity. The shell 51 has an opening connected to the receiving cavity, and the cover plate 53 is used to cover the opening to close the receiving cavity. The electrode assembly 52 of the first aspect of the embodiment of the present application is encapsulated in the receiving cavity. The electrolyte is infiltrated in the electrode assembly 52. The number of electrode assemblies 52 contained in the battery cell 5 may be one or more, which can be adjusted according to demand.

The preparation method of the battery cell of the present application is well known. In some embodiments, the electrode assembly can be placed in an outer package, dried, injected with electrolyte, and subjected to vacuum packaging, standing, forming, shaping and other processes to obtain a battery cell.

Battery

A fourth aspect of the present application provides a battery, which includes the battery cell of the third aspect of the present application.

The battery mentioned in this application refers to a single physical module that includes one or more battery cells to provide higher voltage and capacity. For example, the battery mentioned in this application can be a battery module or a battery pack. The battery generally includes a box for encapsulating one or more battery cells. The box can prevent liquid or other foreign matter from affecting the charging or discharging of the battery cells.

In some embodiments, there may be multiple battery cells in the battery, and the multiple battery cells may be connected in series, in parallel, or in a hybrid connection. A hybrid connection means that the multiple battery cells are both connected in series and in parallel. The multiple battery cells may be directly connected in series, in parallel, or in a hybrid connection, and then the whole formed by the multiple battery cells is accommodated in the box; of course, multiple battery cells may be first connected in series, in parallel, or in a hybrid connection to form a battery module, and then the multiple battery modules are connected in series, in parallel, or in a hybrid connection to form a whole, and then accommodated in the box.

FIG3 is a schematic diagram of a battery module 4 as an example. As shown in FIG3 , there are multiple battery cells 5, and the multiple battery cells 5 are first connected in series, in parallel, or in mixed connection to form a battery module 4. The multiple battery cells 5 in the battery module 4 can be electrically connected through a busbar component to realize the series connection, parallel connection, or mixed connection of the multiple battery cells 5 in the battery module 4. In the battery module 4, the multiple battery cells 5 can be arranged in sequence along the length direction of the battery module 4. Of course, they can also be arranged in any other manner. Further, the multiple battery cells 5 can be fixed by fasteners.

In some embodiments, the battery modules described above may also be assembled into a battery pack, and the number of battery modules contained in the battery pack may be adjusted according to the application and capacity of the battery pack.

FIG. 4 and FIG. 5 are schematic diagrams of a battery pack 1 as an example. As shown in FIG. 4 and FIG. 5 , the battery pack 1 may include a case and a plurality of battery modules 4 disposed in the case. The plurality of battery modules 4 in the battery pack 1 may be electrically connected through a busbar component to achieve series connection, parallel connection, or mixed connection of the plurality of battery modules 4 in the battery pack 1. The case includes an upper case 2 and a lower case 3, and the upper case 2 is used to cover the lower case 3 and form a closed space for accommodating the battery modules 4. The plurality of battery modules 4 may be arranged in the battery box in any manner.

Electrical devices

The present application also provides an electrical device, which includes the secondary battery of the present application. The secondary battery can be used as a power source for the electrical device, and can also be used as an energy storage unit for the electrical device. The electrical device can be, but is not limited to, a mobile device (such as a mobile phone, a laptop computer, etc.), an electric vehicle (such as a pure electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, an electric bicycle, an electric scooter, an electric golf cart, an electric truck, etc.), an electric train, a ship and a satellite, an energy storage system, etc.

FIG6 is an example of an electric device. The electric device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. In order to meet the device's requirements for high power and high energy density, a battery pack or battery module including the secondary battery of the present application may be used.

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

Example

The following examples describe the disclosure of the present application in more detail, and these examples are intended for illustrative purposes only, as it will be apparent to those skilled in the art that various modifications and variations may be made within the scope of the disclosure of the present application. Unless otherwise stated, all parts, percentages, and ratios reported in the following examples are by weight, and all reagents used in the examples are commercially available or synthesized according to conventional methods and can be used directly without further processing, and the instruments used in the examples are commercially available.

Examples 1 to 22

Preparation of composite negative electrode active materials

20g of dopamine was dissolved in 100L tris buffer (pH=8), and mixed with methanol (volume ratio 1:1) to obtain a co-solvent; secondly, m g of high dielectric constant material particles were immersed in the co-solvent solution and reacted for 24h, so that dopamine and the hydroxyl groups on the surface of the high dielectric constant material particles were introduced into the high dielectric constant material particles by dehydration; 10mL of γ-aminopropyltriethoxysilane was added dropwise to 1L of ethanol, and the high dielectric constant material particles with hydroxyl groups were immersed, and the high dielectric constant material particles with amino functional groups were immersed at 80°C for only 6h to obtain high dielectric constant material particles with amino functional groups on the surface;

Dissolve 5 mL of γ-glycidyloxypropyltrimethoxysilane in 1 L of ethanol, add 10 g of silicon-oxygen composite particles, stir for 6 hours, centrifuge, wash, and dry to obtain silicon-oxygen composite particles containing epoxy functional groups;

The high dielectric constant material particles containing amino functional groups and the silicon-oxygen composite particles containing silicon-oxygen functional groups were mixed in 1 L of ethanol solution and reacted at 80° C. for 8 h to obtain a composite negative active material.

Preparation of negative electrode

The composite negative electrode active material, artificial graphite, conductive agent acetylene black, binder SBR, and dispersant sodium carboxymethyl cellulose (CMC) are dissolved in solvent deionized water at a weight ratio of 10:87:1:1:1, and stirred and mixed evenly to prepare a negative electrode slurry; the negative electrode slurry is evenly coated on a 7μm negative electrode current collector copper foil at a coating density of 9.7mg/ ^cm2 , and the negative electrode sheets are obtained after drying, cold pressing, and slitting.

Preparation of positive electrode

The positive electrode active material NCM523 (LiNi _0.5 Co _0.2 Mn _0.3 O ₂ ), the binder polyvinylidene fluoride PVDF, and the conductive agent acetylene black were mixed in a weight ratio of 98:1:1, N-methylpyrrolidone (NMP) was added as a solvent, and the slurry was stirred in a vacuum state until it was uniform; the obtained slurry was coated on a 13 μm aluminum foil with a scraper at an area density of 13.7 mg/cm ² , and then dried at 140°C, cold pressed, and cut to obtain positive electrode sheets.

Preparation of electrolyte

In an argon atmosphere glove box ( _H2O <0.1ppm, _O2 <0.1ppm), organic solvents ethylene carbonate (EC)/ethyl methyl carbonate (EMC) were mixed uniformly in a volume ratio of 3/7, 12.5 wt% (based on the weight of the ethylene carbonate/ethyl methyl carbonate solvent) of _LiPF6 was added and dissolved in the organic solvent, and stirred uniformly to obtain an electrolyte.

Isolation film

A commercially available PP-PE copolymer microporous film (from Zhuogao Electronic Technology Co., Ltd., Model 20) with a thickness of 7 μm and an average pore size of 80 nm was used.

Preparation of secondary batteries

The positive electrode sheet, the separator, and the negative electrode sheet are stacked in order, with the separator placed between the positive and negative electrodes to play a role of isolation, and then wound to obtain an electrode assembly; the electrode assembly is placed in an outer package, the above-mentioned electrolyte is injected and packaged to obtain a secondary battery.

Comparative Example 1

Based on the preparation processes of Examples 1 to 22 and according to the preparation parameters shown in Table 1, the negative electrode sheet, the positive electrode sheet, the electrolyte, the separator and the secondary battery of Comparative Example 1 were prepared.

Comparative Example 2

Based on the preparation processes of Examples 1 to 22, the composite negative electrode active material was replaced with silicon-oxygen composite particles to prepare the negative electrode sheet, positive electrode sheet, electrolyte, separator and secondary battery of Comparative Example 2.

Comparative Example 3

Based on the preparation process of Examples 1 to 22, high dielectric constant material particles are directly mixed with silicon-oxygen composite particles, and the mixture is used to replace the composite negative electrode active material to prepare the negative electrode sheet, positive electrode sheet, electrolyte, isolation membrane and secondary battery of Comparative Example 3.

The preparation parameters of Examples 1 to 22 and Comparative Examples 1 to 3 are shown in Table 1, respectively, wherein the relative dielectric constant ε and the volume average particle size Dv50 of the high dielectric constant material can be measured by the method described in the specification of this application.

The secondary batteries of Examples 1 to 22 and Comparative Examples 1 to 3 were tested as follows. The test results are shown in Table 2.

Test Section

25℃ fast charge cycle life test

At 25°C, the secondary battery was charged at a 4C rate and discharged at a 1C rate, and a continuous cycle charge and discharge test was performed in the range of 3% to 97% SOC until the capacity of the secondary battery was less than 80% of the initial capacity. The number of cycles was recorded as the fast charge cycle life of the secondary battery.

4C rate charging resistance test

At 25C, the secondary battery was discharged to 50% of the initial capacity, left to stand for 30 minutes, and the voltage value V ₁ was recorded. It was charged for 10 seconds at a current A ₀ corresponding to a 4C rate, and the voltage value V ₂ corresponding to the end of charging was recorded. The 4C rate charging resistance R = (V ₂ -V ₁ )/A ₀ .

Fast charging time test

At 35°C, the secondary battery was discharged to a state of 0% SOC, left to stand for 30 minutes, and the SOC when the anode potential reached 0V was monitored by a three-electrode battery. The battery was charged from 5C to 2.3C, and the charging time and the corresponding SOC were recorded every 0.3C. The time from the start of charging to the end of charging was used as the fast charging time of the secondary battery. The real-time rate of Example 1 and Comparative Example 2 and the SOC corresponding to the real-time rate were statistically analyzed to obtain the SOC-rate statistical graph shown in Figure 7.

In addition, the composite negative electrode active material of Example 2 was subjected to XRD test and infrared absorption spectrum test according to the method described in the specification of this application, and the obtained XRD graph and infrared absorption spectrum graph are shown in FIG8 and FIG9 , respectively.

Table 1

Table 2

序号Serial number	快充循环寿命/cyclesFast charge cycle life/cycles	R/ΩR/Ω	快充时间/minFast charging time/min
实施例1Example 1	900900	0.0030.003	11.611.6
实施例2Example 2	10001000	0.0050.005	11.211.2
实施例3Example 3	950950	0.0060.006	11.211.2
实施例4Example 4	910910	0.0090.009	1111
实施例5Example 5	880880	0.010.01	10.810.8
实施例6Example 6	860860	0.0120.012	10.510.5
实施例7Example 7	840840	0.0120.012	10.810.8
实施例8Example 8	880880	0.0140.014	1111
实施例9Example 9	850850	0.0160.016	11.211.2
实施例10Example 10	800800	0.0180.018	11.411.4
实施例11Embodiment 11	600600	0.30.3	12.812.8
实施例12Example 12	700700	0.10.1	1212
实施例13Example 13	750750	0.0080.008	11.811.8
实施例14Embodiment 14	780780	0.0050.005	11.511.5
实施例15Embodiment 15	930930	0.0040.004	11.311.3
实施例16Example 16	940940	0.0030.003	11.211.2
实施例17Embodiment 17	960960	0.0020.002	11.211.2
实施例18Embodiment 18	924924	0.00530.0053	11.711.7
实施例19Embodiment 19	934934	0.0060.006	11.911.9
实施例20 Embodiment 20	952952	0.00650.0065	11.611.6
实施例21Embodiment 21	930930	0.0060.006	11.411.4
实施例22Embodiment 22	920920	0.0050.005	11.511.5
对比例1Comparative Example 1	600600	0.0050.005	1313
对比例2Comparative Example 2	400400	0.0050.005	1414
对比例3Comparative Example 3	400400	0.0080.008	14.514.5

It can be seen from the test results in Table 1 and Table 2 that the composite negative electrode active material of the present application is applied to a secondary battery, which can effectively improve the fast charging performance of the secondary battery.

Specifically, based on the test results of Examples 1 to 6, it can be seen that when other conditions are the same, as the amount of high dielectric constant material particles added increases, the fast charging time of the secondary battery gradually shortens. However, when the content of high dielectric constant material particles is too much, the charging resistance of the secondary battery may increase, thereby having a negative impact on the fast charging cycle life. Therefore, the addition amount of high dielectric constant material particles should be controlled within an appropriate range.

Based on the test results of Examples 2, 7 to 10, it can be seen that when other conditions are the same, as the relative dielectric constant corresponding to the high dielectric constant material particles increases, the fast charging time of the secondary battery gradually shortens. However, as the relative dielectric constant of the high dielectric constant material particles increases, the charging resistance of the secondary battery may increase, thereby affecting the fast charging cycle life of the secondary battery. Therefore, by selecting high dielectric constant material particles with a relative dielectric constant in an appropriate range, the secondary battery can have both good fast charging performance and cycle performance.

Based on the test results of Examples 2, 11 to 17, it can be seen that as the median particle size Dv50 of the high dielectric constant material particles decreases, the fast charge cycle life of the secondary battery is improved, the charging resistance gradually decreases, and the fast charge time is gradually shortened. This may be because as Dv50 decreases, the high dielectric constant material particles can be more closely attached to the surface of the silicon-oxygen composite particles and occupy a smaller space, so that the negative electrode film layer can maintain a higher porosity. As a result, it can not only improve the fast charging performance of the secondary battery, but also help to improve the electrolyte wetting performance of the negative electrode film layer, which is beneficial to improve the dynamic performance of the negative electrode sheet, and then help to reduce the charging resistance of the secondary battery and improve the cycle life of the secondary battery.

Based on the test results of Examples 2 and 18 to 22, it can be seen that, compared with other high dielectric constant materials, the BTO and silicon composite can exhibit good electrical properties in lithium-ion secondary batteries.

In contrast, the surface of the silicon-oxygen composite particles in Comparative Example 2 is not attached with high dielectric constant material particles, and the corresponding fast charging cycle life and fast charging time of the secondary battery are inferior to those of Examples 1 to 22. Although high dielectric constant material particles are attached to the surface of the silicon-oxygen composite particles in Comparative Example 1, the relative dielectric constant of the high dielectric constant material particles is lower than the range specified in the present application, so the fast charging performance of the secondary battery in Comparative Example 1 is also not ideal. Although the relative dielectric constant of the high dielectric constant material particles in Comparative Example 3 is within the range specified in the present application, in Comparative Example 3, the high dielectric constant material particles are simply mixed with the silicon-oxygen composite particles, and are not attached to the surface of the silicon-oxygen composite particles. As a result, the high dielectric constant material particles in Comparative Example 3 may be lost during the preparation of the negative electrode slurry, or unevenly distributed in the negative electrode film layer. Therefore, the fast charging performance of the secondary battery in Comparative Example 3 is also not ideal.

The above is only a specific implementation of the present application, but the protection scope of the present application is not limited thereto. Any technician familiar with the technical field can easily think of various equivalent modifications or replacements within the technical scope disclosed in the present application, and these modifications or replacements should be included in the protection scope of the present application. Therefore, the protection scope of the present application shall be based on the protection scope of the claims.

Claims

A composite negative electrode active material, comprising:

Silicon-oxygen composite particles; and

The high dielectric constant material particles are attached to the surface of the silicon-oxygen composite particles, and the relative dielectric constant ε of the high dielectric constant material particles is ≥70.
The composite negative electrode active material according to claim 1, wherein the high dielectric constant material particles are selected from metal oxoates; optionally, the high dielectric constant material particles are selected from metal oxoates with piezoelectricity, and more optionally, the high dielectric constant material particles are selected from barium titanate, lead titanate, lithium niobate, lead zirconate titanate, lead metaniobate, lead barium lithium niobate or a combination thereof.
The composite negative electrode active material according to claim 1 or 2, wherein the high dielectric constant material particles are barium titanate, and the X-ray powder diffraction pattern of the composite negative electrode active material particles has a characteristic peak at 2θ located at the following position:

20°～24°, 29°～33°, 36°～40°, 43°～47°, 54°～58°, and 62°～68°.
The composite negative electrode active material according to any one of claims 1 to 3, wherein 80≤ε≤200, optionally, 90≤ε≤100.
The composite negative electrode active material according to any one of claims 1 to 4, wherein the volume average particle size Dv50 of the high dielectric constant material particles satisfies: 50nm≤Dv50≤100nm, optionally, 50nm≤Dv50≤80nm.
The composite negative electrode active material according to any one of claims 1 to 5, wherein the mass ratio of the high dielectric constant particles to the silicon-oxygen composite particles is 0.5:100 to 5:100, and can be optionally 0.5:100 to 1.5:100.
The composite negative electrode active material particle according to any one of claims 1 to 6, wherein the silicon-oxygen composite particle is bonded to the high dielectric constant material particle through a covalent bond formed by the reaction of -NH2 and an epoxy group, so that the high dielectric constant material particle is attached to the surface of the silicon-oxygen composite particle.
The composite negative electrode active material according to claim 7, wherein the infrared absorption spectrum of the composite negative electrode active material has characteristic peaks located at the following positions:

3330 cm -1 to 3370 cm -1 , 1180 cm -1 to 1220 cm -1 , and 1080 cm -1 to 1120 cm -1 .
A negative electrode sheet, comprising:

A negative electrode current collector; and

The negative electrode film layer is located on at least one side of the negative electrode current collector, and comprises the composite negative electrode active material according to any one of claims 1 to 8.
The negative electrode sheet according to claim 9, wherein the negative electrode film layer further comprises a second negative electrode active material, and the second negative electrode active material is selected from one or more of a carbon-based negative electrode active material, a silicon-based negative electrode active material or a tin-based negative electrode active material,

Optionally, the mass ratio of the composite negative electrode active material to the second negative electrode active material is 1:96 to 1:2.88.
The negative electrode sheet according to claim 10, wherein the second negative electrode active material is selected from pre-lithiated silicon oxide particles,

Optionally, the pre-lithiated silicon oxide comprises:

Silicon oxide core;

a lithium silicate layer, located on the surface of the silicon oxide core, comprising lithium silicate grains, and silicon nanocrystals and/or silicon dioxide nanocrystals dispersed in the lithium silicate; and

The carbon coating layer is coated on at least a portion of the surface of the lithium silicate layer.
The negative electrode plate according to claim 11, wherein the pre-lithiated silicon oxide satisfies at least one of the following:

(1) Based on the total mass of the lithium silicate grains, the silicon nano-grains and the silicon dioxide, the mass percentage of the lithium silicate grains is 10% to 25%;

(2) The thickness d 1 of the lithium silicate layer satisfies: d 1 ≤35 nm, optionally, 15 nm≤d 1 ≤35 nm;

(3) The thickness d 2 of the carbon coating layer satisfies: d 2 ≤ 25 nm, optionally, 15 nm ≤ d 2 ≤ 25 nm.
An electrode assembly comprises a negative electrode sheet according to any one of claims 9 to 12.
A battery cell comprises a housing and the electrode assembly according to claim 13, wherein the electrode assembly is accommodated in the housing.
A battery comprises a plurality of battery cells according to claim 14.
An electrical device comprises the battery cell according to claim 14, wherein the battery cell is used to provide electrical energy.