WO2023093505A1 - Pole piece and electrochemical device - Google Patents

Abstract

Provided in the present invention are a pole piece and an electrochemical device. The pole piece comprises a substrate. The substrate comprises a current collector and a protective layer arranged on the surface of the current collector. An active substance layer is further arranged on the protective layer. The protective layer comprises a non-active material. The non-active material comprises an inorganic material. The percentage of mass loss in the thermogravimetric analysis of the inorganic material is a, 0.1% ≤ a ≤ 10%,a=(m 0 - m 1)/m 0. m 0 is the mass of the inorganic material before the thermogravimetric analysis, and m 1 is the mass of the inorganic material after the thermogravimetric analysis. The mass after the thermogravimetric analysis is the mass of the inorganic material when experiencing a temperature increase in an inert atmosphere from 25 ± 5 °C to 900 ± 20 °C at a heating rate of 20 ± 2 °C/min. The present invention allows for improving the performance such as safety and recyclability of the electrochemical device.

Description

Electrode and electrochemical device technical field

The invention relates to a pole piece and an electrochemical device, belonging to the field of electrochemical energy storage devices.

Background technique

Electrochemical devices such as lithium-ion batteries have been widely used in energy storage such as consumer electronics and electric vehicles. Among them, lithium-ion batteries have the advantages of high platform voltage, high energy density, no memory effect, and long life. They are widely used in smartphones, Laptops, Bluetooth, wearable devices, etc. However, electrochemical devices such as lithium-ion batteries are inevitably subject to mechanical damage such as acupuncture and heavy impact, and are prone to short circuits when subjected to mechanical damage. If the current collector of one of the positive electrode sheet and the negative electrode sheet is in contact with the other (such as the positive electrode current collector contacts the negative electrode sheet), a short circuit occurs, which poses a greater safety hazard. Therefore, how to reduce the short-circuit risk and improve the safety and other performances of the electrochemical device is a technical problem to be solved urgently by those skilled in the art.

Contents of the invention

The invention provides a pole piece with good safety and other performances, which can effectively solve the problems in the prior art that the positive pole piece and the negative pole piece are prone to short circuit and the resulting poor safety performance of the electrochemical device.

One aspect of the present invention provides a pole piece, including a base, the base includes a current collector and a protective layer arranged on the surface of the current collector, the protective layer is also provided with an active material layer, and the protective layer includes an inactive material, the inactive material includes an inorganic material, the weight loss rate of the inorganic material is a in thermogravimetric analysis, 0.1%≤a≤10%, a=(m ₀ -m ₁ )/m ₀ , m ₀ is the The mass of the inorganic material before the thermogravimetric analysis, m ₁ is the mass of the inorganic material after the thermogravimetric analysis, and the mass after the thermogravimetric analysis is the inorganic material under an inert atmosphere from 25 ± 5 The mass after ℃ is raised to 900±20℃ at a heating rate of 20±2℃/min.

According to an embodiment of the present invention, the protective layer further includes a conductive agent and a binder, based on the total mass of the protective layer, the mass percentage of the inactive material is 60% to 96%, and the conductive agent The mass percentage is 1%-10%, and the mass percentage of the binder is 3%-30%.

According to an embodiment of the present invention, the inorganic material includes at least one of oxides, carbides, nitrides, inorganic salts, and a first carbon coating material, and the first carbon coating material includes a first matrix material and the first carbon layer present on the surface of the first base material, the first base material includes at least one of oxides, carbides, nitrides, and inorganic salts; wherein the oxides include aluminum oxide, At least one of titanium oxide, magnesia, zirconia, stibnite, barium oxide, manganese oxide, and silicon oxide, the carbides include metal carbides and/or non-metal carbides, and the metal carbides include At least one of titanium carbide, calcium carbide, chromium carbide, tantalum carbide, vanadium carbide, zirconium carbide, tungsten carbide, the non-metallic carbide includes boron carbide and/or silicon carbide; the nitride includes metal nitride and /or non-metallic nitrides, the metal nitrides include at least one of lithium nitride, magnesium nitride, aluminum nitride, titanium nitride, and tantalum nitride, and the non-metallic nitrides include boron nitride, five At least one of phosphorus nitride and silicon nitride; the inorganic salt includes carbonate and/or sulfate.

According to an embodiment of the present invention, the inactive material further includes an organic material, and the organic material includes polystyrene, polymethyl methacrylate, polytetrafluoroethylene, and a second carbon coating material, and the The second carbon coating material comprises a second matrix material and a second carbon layer existing on the surface of the second matrix material, and the second matrix material includes polystyrene, polymethyl methacrylate, polytetrafluoroethylene at least one of .

According to an embodiment of the present invention, the thermal decomposition temperature of the inorganic material is greater than or equal to 1200°C.

According to an embodiment of the present invention, the relationship between the thickness H1 of the protective layer and the particle size of the inactive material satisfies H1≥2×D50, where D50 is the particle size distribution based on volume, and the inactive material is on the small particle size side From the beginning to reach the particle size of 50% volume accumulation.

According to an embodiment of the present invention, the particle size of the inactive material satisfies: D50≤2μm, D90≤5μm; D50 is that in the volume-based particle size distribution, the inactive material starts from the small particle size side and reaches a volume accumulation of 50 % particle size; D90 is the particle size at which the inactive material reaches 90% of the volume accumulation from the small particle size side in the volume-based particle size distribution; preferably D50 is 0.05 μm to 1 μm, and D90 is 1 μm to 3 μm.

According to an embodiment of the present invention, the thickness of the protective layer is H1, the thickness of the active material layer is H2, and H1/H2≤1/5.

According to an embodiment of the present invention, the protective layer has a thickness of 0.1 μm˜10 μm.

According to an embodiment of the present invention, both surfaces of the current collector are provided with the protective layer.

According to an embodiment of the present invention, both surfaces of the substrate are provided with the active material layer.

According to an embodiment of the present invention, the active material layer includes an active material, a conductive agent, and a binder, and the protective layer further includes a binder, and the content of the binder in the protective layer is greater than that of the active material layer. content of binder.

According to an embodiment of the present invention, the pole piece is a positive pole piece or a negative pole piece.

According to an embodiment of the present invention, at least one of the first end and the second end of the pole piece, the vertical distance from the protective layer to the outer edge of the current collector is smaller than the distance from the active material layer to the outer edge of the current collector. The vertical distance of the outer edge of the current collector, the first end and the second end are opposite.

According to an embodiment of the present invention, at least one of the first end and the second end of the pole piece, there is an empty foil area between the protective layer and the outer edge of the current collector, and the active material layer It includes a first part and a second part connected to the first part, the first part is arranged on the surface of the protective layer, and the second part is arranged on the surface of the current collector in the empty foil area.

Another aspect of the present invention provides an electrochemical device, including the above pole piece.

In the present invention, a protective layer and an active material layer are sequentially stacked on the surface of the current collector of the pole piece, and an inorganic material whose thermal weight loss rate satisfies 0.1%≤a≤10% is introduced into the protective layer, and acupuncture occurs in the electrochemical device, etc. Under certain conditions, it can maintain good thermal stability, reduce the occurrence of side reactions, maintain the stability of the pole piece, and significantly improve the safety performance of the electrochemical device. The probability of fire failure of the device is greatly reduced; at the same time, the inactive material does not participate in the electrochemical reaction of the electrochemical device, which can reduce the impact on the performance of the electrochemical device such as cycle stability. Therefore, the present invention can significantly improve the safety performance of the electrochemical device, effectively solve the problems such as the fire aging of the electrochemical device such as lithium ion battery under the circumstances of mechanical abuse, etc., and keep the performance such as the cycle of the battery basically unaffected, That is, while improving the safety performance of the electrochemical device, it can maintain or even improve the performance of the electrochemical device, such as the cycle, which is of great significance to the actual industrial application.

Description of drawings

Fig. 1 is the schematic diagram of pole piece structure in one embodiment of the present invention;

Fig. 2 is a schematic diagram of the pole piece structure in another embodiment of the present invention.

Explanation of reference numerals: 01: current collector; 02: protective layer; 03: active material layer.

Detailed ways

In order to enable those skilled in the art to better understand the solution of the present invention, the present invention will be further described in detail below. The specific embodiments listed below are only to describe the principles and features of the present invention, and the examples are only used to explain the present invention, not to limit the scope of the present invention. Based on the embodiments of the present invention, all other implementations obtained by persons of ordinary skill in the art without making creative efforts fall within the protection scope of the present invention.

As shown in Figures 1 and 2, the pole piece of the present invention includes a base, the base includes a current collector 01 and a protective layer 02 arranged on the surface of the current collector 01, an active material layer 03 is also provided on the protective layer 02, and the protective layer 02 includes Inactive materials, inactive materials include inorganic materials, the weight loss rate of inorganic materials by thermogravimetric analysis is a, 0.1%≤a≤10%, a=(m ₀ -m ₁ )/m ₀ , m ₀ is the inorganic material after The mass before thermogravimetric analysis (that is, the mass without thermogravimetric analysis), m ₁ is the mass of the inorganic material after thermogravimetric analysis, and the mass after thermogravimetric analysis is the mass of the inorganic material from 25±5°C under an inert atmosphere. The mass after heating up to 900±20°C at a rate of 20±2°C/min.

During specific implementation, the mass after thermogravimetric analysis (or thermogravimetric analysis) can be the mass when the inorganic material is raised from room temperature to about 900 °C at a heating rate of about 20 °C/min under an inert atmosphere, wherein the temperature, Numerical values such as the heating rate are within the range of conventional error operation in this field.

In the present invention, conventional thermogravimetric analyzers and conventional methods in the field can be used to perform thermogravimetric (TGA) analysis on materials to obtain the weight loss rate of materials. During specific implementation, the iron spoon that comes with the thermogravimetric analyzer is cleaned, and the iron spoon is used for lofting. The TGA analysis process is generally as follows: record the initial mass (that is, the mass before heating) m ₀ of the material powder sample; Put the powder sample into the inert gas-protected analytical furnace of the thermogravimetric analyzer, and program the temperature at a rate of 20±2°C/min. When the temperature rises to 900±20°C, record the mass of the powder sample m ₁ , the weight loss rate of the material is obtained according to a=(m ₀ −m ₁ )/m ₀ . Wherein, the inert atmosphere includes, for example, nitrogen.

For example, the weight loss rate a of the TGA analysis of the above-mentioned inorganic materials can be 0.1%, 0.5%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10% or any combination thereof.

In the present invention, at least one of the front and back surfaces of the current collector 01 is provided with a protective layer 02, and when only one surface of the current collector 01 is provided with the protective layer 02, the protective layer 02 is provided with an active material layer 03 , the other surface of the current collector 01 may be provided with an active material layer or not provided with an active material layer; The active material layer 03 is provided on at least one of the 02, that is, the active material layer 03 may be provided on the protective layer 02 on one surface, or the active material layer 03 may be provided on the protective layers 02 on both surfaces. Relatively speaking, a protective layer 02 is provided on both surfaces of the current collector 01, which is beneficial to further improving the safety of the pole piece, and an active material layer 03 is provided on both surfaces of the substrate, which is beneficial to improving the energy density of the pole piece, etc. performance. Therefore, in some preferred embodiments, both surfaces of the current collector 01 are provided with protective layers 02 , and both surfaces of the substrate are provided with active material layers 03 .

In the present invention, the inactive material plays a supporting role in the protective layer 02, which is used as the skeleton support of the protective layer 02, and is generally the main component of the protective layer 02. If the content of the inactive material in the protective layer 02 is too small, it will cause The structural stability of the entire protective layer 02 is poor, and it is easy to be crushed under pressure in the rolling process during the pole piece preparation process or to be crushed and destroyed during the use of the pole piece. Therefore, the inactive material in the protective layer 02 The mass content is greater than 50%, further not lower than 60%, for example, 60% to 96%.

In addition, the protective layer 02 may also include a conductive agent and a binder. The binder is used to bond the inactive materials, conductive agents and other components in the protective layer 02 together to form a coating, and connect the protective layer 02 with the current collector. 01 are bonded together to further improve the stability of the protective layer 02 and the adhesion between the current collector 01, thereby improving the stability and safety of the pole piece. The conductive agent can build an electronic conductive network, especially when When the protective layer 02 is located between the surface of the current collector 01 and the active material layer 03, it can serve as an electronic pathway connecting the current collector 01 and the active material layer 03, which is beneficial to the function of the current collector 01 and improves the performance of the electrode sheet such as rate capability. If the mass content of the binder in the protective layer 02 is too small, it will affect the cohesive force between the particles in the protective layer 02 and the cohesive force between the protective layer 02 and the current collector 01, and if the mass content of the binder If it is too large, the pole piece will become brittle, and the compaction density of the pole piece will be reduced, which will affect the energy density of the pole piece. In addition, the conductive agent in the protective layer 02 is to provide a certain electronic conductivity for the protective layer 02. If If its content is too low, the conductive performance of the protective layer 02 will be insufficient, which will affect the electrical properties of the pole piece. If the mass content of the conductive agent is too large, it will also affect the protection of the protective layer 02 to the pole piece to a certain extent. Function, for example, when the pole piece used in the electrochemical device is short-circuited with the pole piece of another polarity, the protective layer 02 of the pole piece has high conductivity, and it is connected with the pole piece of another polarity Contact will cause intense heat generation at the short-circuit point, causing thermal runaway. Taking these factors into consideration, in some preferred embodiments, based on the total mass of the protective layer 02, the mass percentage of the inactive material can be 60% to 96%, the mass percentage of the conductive agent can be 1% to 10%, and the bonding The mass percentage of the agent can be 3%-30%, that is, the mass content of the inactive material, the conductive agent and the binder in the protective layer 02 are 60%-96%, 1%-10%, and 3%-30%, respectively. Optionally, in the protective layer 02, the mass content of the inactive material is, for example, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 96%, or any combination thereof, The mass content of the conductive agent is, for example, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, or any two thereof, the binder The mass content is, for example, 3%, 7%, 10%, 15%, 20%, 25%, 30%, or any combination thereof. Preferably, the mass content of the inactive material in the protective layer 02 is greater than the mass content of the binder in the protective layer 02 , and the mass content of the binder in the protective layer 02 is greater than the mass content of the conductive agent in the protective layer 02 .

In the present invention, the inactive material is a material that does not participate in the electrochemical reaction in the charging and discharging process of the pole piece/electrochemical device (relative to the function of the active material of the active material layer of the pole piece), which can ensure the electrochemical reaction of the protective layer 02. Stability, during the charging and discharging process of the pole piece, it will not continue to deteriorate and affect the service life of the pole piece, and it also serves as the skeleton support of the protective layer. In some embodiments, the inorganic material in the protective layer 02 may include at least one of oxides, carbides, nitrides, inorganic salts, and the first carbon coating material, and the first carbon coating material includes the first matrix material and the first carbon layer present on the surface of the first base material, the first base material includes at least one of oxides, carbides, nitrides, and inorganic salts; wherein the oxides include aluminum oxide (Al ₂ O ₃ ), At least one of titanium oxide, magnesium oxide (MgO), zirconium oxide (ZrO), styroite (Sb ₂ S ₂ O), barium oxide (BaO), manganese oxide, silicon oxide, and carbides including metal carbides And/or non-metallic carbides, metal carbides include at least one of titanium carbide, calcium carbide, chromium carbide, tantalum carbide, vanadium carbide, zirconium carbide, tungsten carbide, non-metallic carbides include boron carbide and/or silicon carbide The nitrides include metal nitrides and/or non-metal nitrides, the metal nitrides include at least one of lithium nitride, magnesium nitride, aluminum nitride, titanium nitride, and tantalum nitride, and the non-metal nitrides include nitrogen At least one of boron nitride, phosphorus pentanitride, and silicon nitride; inorganic salts include carbonates and/or sulfates.

In the present invention, the above-mentioned inorganic materials generally have good thermal stability and high thermal decomposition temperature. In some embodiments, the thermal decomposition temperature of the inorganic material in the protective layer 02 is greater than or equal to 1200°C. For example, thermal Aluminum oxide, titanium oxide, magnesium oxide, manganese oxide, silicon oxide, etc., whose decomposition temperature is greater than or equal to 1200 ° C, choose the inorganic material with a higher thermal decomposition temperature, so that the protective layer 02 can maintain a good temperature in a large temperature range. Stability, and further improve the performance of the pole piece and the safety of the electrochemical device. When the temperature is higher than normal temperature, or the decomposition reaction that occurs when the temperature is heated is called thermal decomposition, the thermal decomposition temperature generally refers to the temperature when the material begins to decompose. The present invention can measure the thermal decomposition temperature of the inorganic material according to the conventional methods in the art. For example, a thermogravimetric analyzer can be used to perform thermogravimetric analysis on inorganic materials. Specifically, the temperature of the inorganic material is raised from room temperature (25±5°C) at a rate of about 20°C/min in an inert atmosphere to obtain a TG curve. The abscissa of the TG curve is the temperature, and the ordinate is the remaining mass of the material during the heating process. Generally, the temperature corresponding to the first inflection point of the TG curve is the thermal decomposition temperature of the material. During specific implementation, the iron spoon that comes with the thermogravimetric analyzer is cleaned, and the iron spoon is used for lofting. The thermogravimetric analysis process is generally as follows: the iron spoon is used to put the powder sample into the analysis furnace protected by the inert gas of the thermogravimetric analyzer. Within, the temperature is programmed at a heating rate of 20±2° C./min, and the TG curve is measured; wherein, the inert atmosphere includes, for example, nitrogen.

In some embodiments, the Vickers microhardness (or micro Vickers hardness) of the inorganic material in the protective layer 02 is greater than or equal to 3.5GPa, which is conducive to being squeezed on the protective layer 02 (such as in the pole piece preparation process The extrusion effect produced by the rolling process in the process or the extrusion effect received during the use of the pole piece, etc.) can maintain the basic shape of the protective layer 02, so that it can better maintain the original shape and avoid the partial protective layer 02 being overwhelmed. Squeeze to break away from the current collector 01, causing the current collector 01 to contact with the pole piece of the other polarity in the electrochemical device to cause a short circuit, thereby improving the performance of the pole piece and the safety of the electrochemical device. For example, Vickers can be selected Aluminum oxide, titanium oxide, magnesium oxide, manganese oxide, silicon oxide, etc. whose microhardness is greater than or equal to 3.5GPa.

In the present invention, the Vickers microhardness of the material can be measured by a conventional method in the art, for example, the Vickers microhardness tester is used to measure the Vickers microhardness of the material under the condition that the load is about 4.91N and the holding time is about 10s. The microhardness can be measured at least 3 times, and then the average value of the at least 3 measurement results is taken as the final Vickers microhardness value of the material to be tested. During specific implementation, the material to be tested is powdery, and at least 3 powder samples, then measure the Vickers microhardness of each sample separately, and then calculate the average value of the measurement results corresponding to all powder samples, that is, obtain the Vickers microhardness of the material to be tested.

In addition, the above-mentioned inactive materials may also include organic materials, and the organic materials may be tiny particles formed of polymer materials, and the organic materials include polystyrene, polymethyl methacrylate, polytetrafluoroethylene and the second Two carbon coating materials, the second carbon coating material comprises a second base material and a second carbon layer present on the surface of the second base material, the second base material includes polystyrene, polymethyl methacrylate, polytetrafluoroethylene at least one of ethylene.

In the present invention, the first carbon coating material can be a composite material prepared by coating the first carbon layer on the surface of the first base material through a carbon coating process, and the second carbon coating material can be a carbon coating process through the carbon coating process. The composite material is prepared by coating the surface of the second matrix material with the second carbon layer. The carbon coating process is a conventional process in the field and will not be repeated here.

Specifically, the above-mentioned inactive materials are granular, the inorganic materials are inorganic particles, and the organic materials are organic particles. The inactive materials with small particle sizes are not easy to be removed from the surface of the current collector 01 during mechanical actions such as nailing/acupuncture. Falling off, further improving the stability and safety of the pole piece, in some preferred embodiments, the particle size of the inactive material satisfies: D50≤2μm, D90≤5μm; D50 is in the particle size distribution of the volume basis, the inactive material Starting from the small particle diameter side, the particle diameter reaching 50% of the volume accumulation; D90 is the particle diameter of the inactive material starting from the small particle diameter side and reaching 90% of the volume accumulation in the volume-based particle size distribution; preferably, D50 is 0.05 μm～1μm, such as 0.05μm, 0.1μm, 0.2μm, 0.3μm, 0.4μm, 0.5μm, 0.6μm, 0.7μm, 0.8μm, 0.9μm, 1μm or any combination thereof, D90 is 1μm～ 3 μm, such as 1 μm, 1.5 μm, 2 μm, 2.5 μm, 3 μm or any combination thereof.

According to the research of the present invention, the relationship between the thickness H1 of the protective layer 02 and the particle size of the inactive material satisfies H1≥2×D50. Under this condition, it is beneficial to make the protective layer 02 in its thickness direction (the direction perpendicular to the surface of the current collector 01) At least two inactive material particles are evenly distributed on the surface, which is equivalent to forming at least two single-layer protective layers 02 (the average number of inactive material particles in each single-layer protective layer 02 in its thickness direction is one), which is more conducive to protection The function of layer 02 can improve the safety and other performances of the pole piece.

After further research, the thickness of the protective layer 02 is H1, the thickness of the active material layer 03 is H2, H1/H2≤1/5, preferably H1/H2≤1/10, which can improve the safety of the electrochemical device while maintaining its It has high energy density and other properties.

In some embodiments, the thickness of the protective layer 02 may be 0.1 μm to 10 μm, such as 0.1 μm, 0.5 μm, 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm or any two of them range of composition.

In some embodiments, the resistivity of the protective layer 02 can be 500-5000Ω·cm, and the resistivity of the protective layer 02 is affected by various factors such as the thickness of the protective layer 02, the mass content of the conductive agent, and the type of inactive material. As a result, if the resistivity of the protective layer 02 is too large, it will affect the electrical performance of the pole piece and the electrochemical device, and if the resistivity of the protective layer 02 is too small, it will affect the safety performance of the pole piece and the electrochemical device. The resistivity of 02 is 500-5000Ω·cm, which can take into account the safety and electrical performance of electrochemical devices.

Generally, the active material layer 03 includes an active material, a conductive agent and a binder, and the content of the binder in the protective layer 02 is greater than the content of the binder in the active material layer 03, which is beneficial to further improve the stability of the pole piece. , safety and cycle performance.

Optionally, the binders in the protective layer 02 and the active material layer 03 respectively include polyvinylidene fluoride (PVDF), carboxylic acid modified polyvinylidene fluoride (PVDF), polymethyl methacrylate (PMMA), At least one of polyacrylonitrile (PAN), polyacrylates, and polyimide (PI), wherein the carboxylic acid-modified PVDF includes acrylic acid-modified PVDF. The binders in the protective layer 02 and the active material layer 03 may be the same or different. In some preferred embodiments, the binder in the protective layer 02 includes carboxylic acid-modified PVDF, more preferably acrylic-modified PVDF.

Optionally, the conductive agents in the protective layer 02 and the active material layer 03 respectively include at least one of conductive carbon black, acetylene black, graphite, graphene, carbon nanotubes, and carbon nanofibers. The conductive agents in the protective layer 02 and the active material layer 03 may be the same or different.

In addition, the active material layer may further include a dispersant, such as sodium carboxymethylcellulose and the like.

In the present invention, the above-mentioned pole piece may be a positive pole piece or a negative pole piece. The active material in the active material layer 03 is a material that participates in the electrochemical reaction during the charging and discharging process of the electrode sheet/electrochemical device. When the above-mentioned electrode sheet is a positive electrode sheet, the active material layer 03 is a positive electrode active material layer 03, wherein The active material is a positive electrode active material, such as a positive electrode active material that provides lithium ions. The positive electrode active material may include a lithium positive electrode composite metal oxide (that is, an inorganic material containing lithium), such as lithium cobaltate (LiCoO ₂ ), nickel acid At least one of lithium (LiNiO ₂ ), lithium manganese oxide (LiMn ₂ O ₄ ), lithium iron phosphate (LiFePO ₄ ), and ternary materials. The chemical formula of the ternary material can be LiNi _x Co _y Mn _z O ₂ , x +y+z=1, the ternary material includes, for example, nickel-cobalt-manganese ternary material and/or nickel-cobalt-aluminum ternary material and the like. When the above-mentioned pole piece is a negative pole piece, the above-mentioned active material layer 03 is a negative electrode active material layer 03, and the active material therein is a negative electrode active material, and the negative electrode active material can include artificial graphite, natural graphite, soft carbon, hard carbon, mesophase At least one of carbon microspheres (MCMB), silicon, silicon-carbon composites, silicon oxide, lithium titanate, and lithium metal.

In addition, when the above-mentioned electrode sheet is a positive electrode sheet, the above-mentioned current collector 01 is a positive electrode current collector, which can be an aluminum foil composed of aluminum as the main component, or an aluminum foil laminated with other materials (such as polymer materials, etc.) A composite current collector, or a composite current collector including aluminum foil and a conductive carbon layer coated on the surface of the aluminum foil, etc., wherein the mass content of aluminum in the aluminum foil is generally not less than 95%. When the above-mentioned electrode sheet is a negative electrode sheet, the above-mentioned current collector 01 is a negative electrode current collector, for example, includes copper foil and the like.

In the present invention, preferably the active material layer 03 is disposed on the surface of the protective layer 02 (that is, the protective layer 02 is located between the surface of the current collector 01 and the active material layer 03), and the active material layer 03 may not completely cover the active material layer 03 (as shown in Figure 1 shown), alternatively, the active material layer 03 may completely cover the active material layer 03 (as shown in FIG. 2 ). Specifically, in some embodiments, as shown in FIG. 1 , at least one of the first end and the second end of the pole piece, the vertical distance from the protective layer 02 to the outer edge of the current collector 01 is smaller than the distance from the active material layer 03 to the outer edge of the current collector 01. The vertical distance from the outer edge of the current collector 01, that is, the distance from the protective layer 02 to the outer edge of the current collector 01 in the direction parallel to the direction from the first end to the second end is smaller than the distance from the active material layer 03 to the outer edge of the current collector 01 in parallel to the direction from the first end to the second end. The distance in the direction from one end to the second end, the first end is opposite to the second end, and the orthographic projection of the protective layer 02 parallel to the surface of the current collector 01 generally covers the orthographic projection of the active material layer 03 parallel to the surface of the current collector 01 . In some other embodiments, as shown in FIG. 2, at least one of the first end and the second end of the pole piece, there is an empty foil area between the protective layer 02 and the outer edge of the current collector 01, and the active material layer 03 Including a first part and a second part connected to the first part, the first part is arranged on the surface of the protective layer 02, and the second part is arranged on the surface of the current collector 01 in the empty foil area (that is, the second part is located between the protective layer 02 and the current collector 01 On the surface of the current collector (01) between the outer edges, the first end and the second end are opposite.

The pole piece of the present invention also includes a tab, and the setting position of the tab can be a conventional tab setting position in the art, for example, it can be set at the end of the pole piece (such as at least one of the above-mentioned first end and the second end) , or set in the middle of the pole piece and other positions. The pole piece of the present invention can be prepared by conventional methods in the field such as the coating method. In practice, the raw materials of the protective layer 02 can be mixed with the first solvent to prepare the first slurry, and then the first slurry can be coated At the preset position on the surface of the current collector 01, the protective layer 02 is formed after drying to obtain the above-mentioned substrate; the raw materials of the active material layer 03 are mixed with the second solvent to prepare a second slurry, and then the second slurry is coated The cloth is placed on the preset position on the surface of the substrate, and the active material layer 03 is formed after drying, rolling and other processes, and then the tab is welded on the preset position of the tab to obtain the pole piece. Among them, the tab preset position can be reserved during the above coating process, or after the coating is completed, the coating at the tab preset position can be washed off, and then the tab can be welded at the tab preset position; the first solvent It can be the same as or different from the second solvent, for example, it includes N-methylpyrrolidone (NMP) and the like.

The electrochemical device of the present invention includes the above pole piece. Specifically, the electrochemical device of the present invention may include a positive electrode sheet with the above-mentioned structural design (that is, the above-mentioned electrode sheet is a positive electrode sheet), or may include a negative electrode sheet with the above-mentioned structural design (that is, the above-mentioned electrode sheet is a negative electrode sheet), or may simultaneously It includes a positive electrode sheet with the above-mentioned structural design and a negative electrode sheet with the above-mentioned structural design (that is, the above-mentioned electrode sheet includes a positive electrode sheet and a negative electrode sheet). When the above-mentioned pole piece is a positive pole piece, the above-mentioned electrochemical device also includes a negative pole piece, and the negative pole piece can be a conventional negative pole piece in the art; when the above-mentioned pole piece is a negative pole piece, the above-mentioned electrochemical device also includes a positive pole piece, and the positive pole piece It can also be a conventional positive electrode sheet in the field, which is not particularly limited in the present invention.

Specifically, the electrochemical device of the present invention may be a battery, such as a lithium-ion battery or the like. In general, the electrochemical device includes an electrolyte, an electric core, and a packaging material for encapsulating the electric core. The electric core includes a positive electrode sheet, a negative electrode sheet, and a separator (or diaphragm) between the positive electrode sheet and the negative electrode sheet. ), the electrochemical device can be made according to conventional methods in the art, for example, the above-mentioned positive electrode sheets, separators, and negative electrode sheets are stacked in sequence and then wound or stacked into electric cores, and then packaged with packaging materials (such as aluminum-plastic films, etc. ) Encapsulate the cell and inject the electrolyte, and then make an electrochemical device after sealing, forming and other processes.

Optionally, the above-mentioned electrolytic solution may include a non-aqueous electrolytic solution, and its components may include a non-aqueous solvent and a lithium salt, the non-aqueous solvent includes carbonates and/or carboxylates, and the lithium salt includes lithium hexafluorophosphate (LiPF ₆ ) and and/or lithium tetrafluoroborate (LiBF ₄ ). In addition, the electrolyte may also contain additives, which may be conventional electrolyte additives in the field, which is not particularly limited in the present invention.

Alternatively, the isolation film may include a base film including, for example, a PE film formed of polyethylene (PE), a PP film formed of polypropylene (PP), a PI film formed of polyimide (PI). At least one of them, in addition, a reinforcement layer can also be provided on the surface of the base film as required, the reinforcement layer can include a binder layer and/or a ceramic layer, the binder layer contains a binder, and the ceramic layer contains a ceramic Relatively speaking, the introduction of a binder layer into the separator can improve the adhesion of the separator, and the introduction of a ceramic layer into the separator can improve the heat resistance and other properties of the separator. Wherein, also can contain binding agent in the ceramic layer, in order to be beneficial to bond ceramic particles to form ceramic layer and improve the cohesive force between ceramic layer and base film, the binding agent in adhesive layer and ceramic layer can comprise respectively Polytetrafluoroethylene, polyurethane, polyvinylidene fluoride, polyimide, polyacrylonitrile, polymethyl methacrylate, styrene-butadiene rubber, lithium polystyrene sulfonate, epoxy resin, styrene-acrylic latex, polyacrylic acid, At least one of polyethylene oxide, the binder in the binder layer and the ceramic layer can be the same or different; the ceramic particles in the ceramic coating can include aluminum oxide, magnesium oxide, boehmite, magnesium hydroxide, At least one of barium sulfate, barium titanate, zirconia, magnesium aluminate, silicon oxide, hydrotalcite, silicon oxide, tourmaline, zinc oxide, calcium oxide, and fast ion nanoparticles.

In order to make the purpose, technical solutions and advantages of the present invention clearer, the technical solutions of the present invention will be clearly and completely described below in conjunction with specific embodiments. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all of them. Example. Based on the embodiments of the present invention, all other embodiments obtained by persons of ordinary skill in the art without making creative efforts belong to the protection scope of the present invention.

In the following examples, the thermogravimetric analyzer performs TGA analysis on the inorganic material to obtain the weight loss rate of the inorganic material. The analysis process is briefly described as follows: record the initial mass (ie, the mass before heating) m ₀ of the material powder sample; Put the powder sample into the nitrogen-protected analysis furnace of the thermogravimetric analyzer with a clean iron spoon, and program the temperature at a rate of 20°C/min. When it reaches 900°C, record the mass _m of the powder sample (m ₁ is the mass of the inorganic material when the temperature rises from room temperature to 900°C at a rate of 20°C/min under an inert atmosphere), and the weight loss rate of the material is obtained according to a=(m ₀ -m ₁ )/m ₀ .

In the following examples, a thermogravimetric analyzer is used to measure the thermal decomposition temperature of inorganic materials. The test process is as follows: a clean iron spoon is used to put the powder sample into the analytical furnace protected by nitrogen gas of the thermogravimetric analyzer, and the temperature is 20 ° C / The heating rate of min is used to program the temperature, and the TG curve is measured. The temperature corresponding to the first inflection point of the TG curve is the thermal decomposition temperature of the inorganic material (ie, the temperature when the inorganic material begins to decompose).

Example 1

1. Preparation of positive electrode sheet

Mix aluminum oxide, acrylic modified PVDF, and carbon black in a mass ratio of 62:30:8 (that is, the mass content of aluminum oxide in the formed protective layer is about 62%, the mass content of acrylic modified PVDF is about 30%, and the carbon black The mass content of black is about 8%), NMP is added therein, stirred uniformly, makes the first slurry; The first slurry is coated on the positive and negative surface of aluminum foil, forms protective layer after drying, obtains base;

Mix LCO, PVDF, and carbon black according to the mass ratio of 96:2:2, add NMP to it, stir evenly, and prepare the second slurry; apply the second slurry on the front and back surfaces of the substrate (that is, aluminum foil The surface of the protective layer on the positive and negative surfaces), after drying and rolling, the positive electrode active material layer is formed; after the positive electrode tab is welded at the preset tab position of the aluminum foil, the positive electrode sheet is obtained;

Among them, the weight loss a and thermal decomposition temperature of the TGA analysis of the alumina used are shown in Table 2 and Table 3 respectively, D50 of alumina = 0.7 μm, D90 of alumina = 1.2 μm, the thickness of the protective layer H1 = 2 μm, the positive electrode activity Thickness H2 of the substance layer = 60 μm.

2. Preparation of negative electrode sheet

Mix artificial graphite, styrene-butadiene rubber, sodium carboxymethyl cellulose, and carbon black with water at a mass ratio of 96:1.5:1.5:1, and stir evenly to make negative electrode slurry; coat the negative electrode slurry on the copper foil The positive and negative surfaces are dried and rolled to form a negative electrode active material layer, and the negative electrode tab is welded to the preset tab position of the copper foil to obtain a negative electrode sheet.

3. Preparation of Li-ion battery

The above-mentioned positive electrode sheet, separator, and negative electrode sheet are stacked in order and wound into a bare cell, and the bare cell is packaged with aluminum-plastic film, and the seal is sealed after injecting electrolyte into it from the seal, and then undergoes chemical formation and other processes , Lithium-ion batteries were produced.

With reference to the preparation process of Example 1, the positive electrode sheet, negative electrode sheet and lithium ion battery of Examples 2 to 9, Comparative Examples 1 to 8 were obtained, wherein:

The difference between Examples 2-Example 5, Comparative Example 1-Comparative Example 4 and Example 1 is that the mass content of alumina, acrylic modified PVDF, and carbon black in the protective layer of the positive electrode sheet are different, as shown in Table 1 for details, and the rest Condition is substantially identical with embodiment 1;

The difference between Comparative Example 5 and Example 1 is that the positive electrode sheet is not provided with a protective layer (that is, only the positive electrode active material layer), and the remaining conditions are basically the same as in Example 1;

The difference between Examples 6-Example 7, Comparative Example 6-Comparative Example 7 and Example 1 is that the thermal weight loss rate a of the TGA analysis of the aluminum oxide used to form the protective layer of the positive electrode sheet is different, see Table 2 for details, and the remaining conditions Substantially the same as Example 1;

The difference between Examples 8-9 and Comparative Example 8 and Example 1 is that the thermal decomposition temperature of the aluminum oxide used to form the protective layer of the positive electrode sheet is different, and the rest of the conditions are basically the same as Example 1.

The conventional performance test methods in this field were used to perform performance tests on the batteries of each embodiment and comparative examples. The results are shown in Table 1 and Table 2. The test process is briefly described as follows:

(1) Needle piercing test: fully charge the battery, put the fully charged battery on the nail piercing test equipment, and then start the equipment, so that the nail (diameter 3mm) penetrates the center of the battery perpendicular to the battery plane at a speed of 130mm/s , exit after staying for 10 minutes, the battery does not catch fire and is regarded as passed, each test is 10, the pass rate of the needle test = N ₁ /10, N ₁ is the number of passed batteries;

(2) Rate performance test: discharge the battery at a rate of 0.5C to 3.0V, and after standing for 5 minutes, charge the battery at a rate of 0.5C to the upper limit voltage, and then charge at a constant voltage with a cut-off current of 0.02C; after standing for 5 minutes , discharge the battery at a rate of 0.2C to 3.0V, and record the battery capacity as C0; after standing for 5 minutes, charge the battery at a rate of 0.5C to the upper limit voltage, and then charge at a constant voltage with a cut-off current of 0.02C; after standing for 5 minutes , discharge the battery to 3.0V at a rate of 0.5C, and record the battery capacity as C1; C1/C0 is the discharge capacity ratio of 0.5C/0.2C, which is used to evaluate the battery rate discharge capacity;

(3) Energy density test: fully charge the battery, then discharge it at 0.2C to 3.0V, and record the discharged energy as E; the volumetric energy density of the battery ED=E/V; where, V is the volume of the battery, V is obtained by measuring the length L, width W, and height H, and V=L×W×H.

Table 1

* indicates that ΔED is the difference between the volume energy density ED of the battery of this example and the battery of Comparative Example 5.

Table 2

Example	The weight loss rate of alumina in the protective layer a	Needle penetration test pass rate (N 1 /10)
Example 1	0.5%	10/10
Example 6	3.5%	10/10
Example 7	8.4%	10/10
Comparative example 6	12.1%	8/10
Comparative example 7	18.0%	6/10

table 3

Example	Thermal decomposition temperature of alumina in protective layer	Needle penetration test pass rate (N 1 /10)
Example 1	1800°C	10/10
Example 8	1500℃	10/10
Example 9	1200℃	10/10
Comparative example 8	750°C	4/10

It can be seen from Examples 1 to 5 and Comparative Example 5 that setting the above protective layer can significantly improve the safety performance of the battery, while maintaining good rate performance and energy density;

It can be seen from Example 1 and Comparative Example 1 that if the content of the binder in the protective layer is too large, it will affect the compaction density of the positive electrode sheet, thereby losing the energy density of the battery;

It can be seen from Example 1 and Comparative Example 2 that if the conductive agent content of the protective layer is too large, the passing rate of the acupuncture test will be reduced and the safety performance of the battery will be affected;

It can be seen from Example 1 and Comparative Example 3 that if the binder content of the protective layer is too small, the adhesion of the protective layer will be deteriorated, the passing rate of the acupuncture test will be reduced, and the safety performance of the battery will be affected;

It can be seen from Example 1 and Comparative Example 4 that the conductive agent content of the protective layer is too small, and the electronic conductivity of the protective layer becomes poor, resulting in poor rate discharge capability of the battery and affecting the electrical performance of the battery;

From Example 1, Examples 6-7, and Comparative Examples 6-7, it can be seen that inorganic materials (alumina) with different weight loss rates in the protective layer have an important impact on the safety of pole pieces and electrochemical devices. Inorganic materials satisfying 0.1%≤a≤10% can effectively improve the safety performance of pole pieces and batteries; in addition, after testing, the rate performance and energy density loss test results of Examples 6 to 7 are basically equivalent to those of Example 1, and further It shows that the introduction of inorganic materials that meet the above weight loss rate into the protective layer on the surface of the current collector can take into account the characteristics of maintaining the energy density and rate performance of the battery;

From Example 1, Examples 8 to 9, and Comparative Example 8, it can be seen that inorganic materials (aluminum oxide) with different thermal decomposition temperatures in the protective layer have an important impact on the safety of pole pieces and electrochemical devices. Inorganic materials not less than 1200°C can effectively improve the safety performance of pole pieces and batteries; in addition, after testing, the rate performance and energy density loss test results of Examples 8 to 9 are basically equivalent to those of Example 1, further illustrating that in the current collector The introduction of inorganic materials with a thermal decomposition temperature of not less than 1200°C in the protective layer on the surface can take into account the characteristics of maintaining the energy density and rate performance of the battery.

In addition, the positive electrode sheet in Example 1 has the structure shown in Figure 1. After testing, when the positive electrode sheet in Example 1 has the structure shown in Figure 2, it can achieve basically the same effect as the positive electrode sheet with the structure shown in Figure 1, and details will not be repeated here.

Embodiments of the present invention have been described above. However, the present invention is not limited to the above-mentioned embodiments. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention shall be included within the protection scope of the present invention.

Claims (10)

1. A pole piece, characterized in that it includes a base, the base includes a current collector and a protective layer arranged on the surface of the current collector, the protective layer is also provided with an active material layer, the protective layer includes an inactive material, the The inactive material includes an inorganic material, and the weight loss rate of the inorganic material in thermogravimetric analysis is a, 0.1%≤a≤10%, a=(m ₀ -m ₁ )/m ₀ , and m ₀ is the inorganic material The mass before the thermogravimetric analysis, m ₁ is the mass of the inorganic material after the thermogravimetric analysis, the mass after the thermogravimetric analysis is the inorganic material in an inert atmosphere from 25 ± 5 ° C at 20 The mass after the heating rate of ±2°C/min rises to 900±20°C.
2. The pole piece according to claim 1, wherein the protective layer further includes a conductive agent and a binder, and based on the total mass of the protective layer, the mass percentage of the inactive material is 60% to 96%. , the mass percentage of the conductive agent is 1%-10%, and the mass percentage of the binder is 3%-30%.
3. The pole piece according to claim 1 or 2, wherein the inorganic material comprises at least one of oxides, carbides, nitrides, inorganic salts, and the first carbon coating material;

   The first carbon coating material comprises a first base material and a first carbon layer present on the surface of the first base material, and the first base material includes at least one of oxides, carbides, nitrides, and inorganic salts. One; wherein, the oxide includes at least one of aluminum oxide, titanium oxide, magnesium oxide, zirconium oxide, stimbine, barium oxide, manganese oxide, silicon oxide, and the carbide includes metal carbide and /or non-metallic carbides, the metal carbides include at least one of titanium carbide, calcium carbide, chromium carbide, tantalum carbide, vanadium carbide, zirconium carbide, tungsten carbide, the non-metallic carbides include boron carbide and/or or silicon carbide; the nitrides include metal nitrides and/or non-metal nitrides, and the metal nitrides include at least one of lithium nitride, magnesium nitride, aluminum nitride, titanium nitride, and tantalum nitride , the non-metallic nitride includes at least one of boron nitride, phosphorus pentanitride, and silicon nitride; the inorganic salt includes carbonate and/or sulfate; and/or,

   The inactive material also includes an organic material, and the organic material includes polystyrene, polymethyl methacrylate, polytetrafluoroethylene, and a second carbon coating material, and the second carbon coating material includes the second carbon coating material. A second matrix material and a second carbon layer existing on the surface of the second matrix material, the second matrix material includes at least one of polystyrene, polymethyl methacrylate, and polytetrafluoroethylene.
4. The pole piece according to claim 1 or 2, characterized in that the thermal decomposition temperature of the inorganic material is greater than or equal to 1200°C.
5. The pole piece according to claim 1, characterized in that,

   The relationship between the thickness H1 of the protective layer and the particle size D50 of the inactive material satisfies H1≥2×D50; and/or,

   The particle size of the inactive material satisfies: D50≤2μm, D90≤5μm.
6. The pole piece according to claim 5, characterized in that,

   The particle size of the inactive material satisfies: D50 is 0.05 μm-1 μm, and D90 is 1 μm-3 μm.
7. The pole piece according to claim 1 or 5, characterized in that,

   The thickness of the protective layer is H1, the thickness of the active material layer is H2, H1/H2≤1/5; and/or,

   The thickness of the protective layer is 0.1 μm˜10 μm.
8. The pole piece according to claim 1, characterized in that,

   Both surfaces of the current collector are provided with the protective layer; and/or,

   Both surfaces of the substrate are provided with the active material layer; and/or

   The active material layer includes an active material, a conductive agent and a binder, and the protective layer further includes a binder, and the content of the binder in the protective layer is greater than that in the active material layer.
9. The pole piece according to claim 1, characterized in that,

   At least one of the first end and the second end of the pole piece, the vertical distance from the protective layer to the outer edge of the current collector is smaller than the vertical distance from the active material layer to the outer edge of the current collector, the first and second ends are opposite; or,

   At least one of the first end and the second end of the pole piece, there is an empty foil area between the protective layer and the outer edge of the current collector, the active material layer includes a first part, and the first part and the first part A connected second part, the first part is arranged on the surface of the protective layer, and the second part is arranged on the surface of the current collector in the empty foil area.
10. An electrochemical device, characterized by comprising the pole piece according to any one of claims 1-9.

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