CN112670513A - Cathode electrode and preparation method and application thereof - Google Patents

Abstract

The invention discloses a cathode electrode and a preparation method and application thereof, wherein the preparation method comprises the following steps: a cathode current collector; a cathode active material layer coated on the cathode current collector, the cathode active material layer including a cathode active material, a binder, a conductive agent, and being decomposed to generate CO at high temperature₂The additive of (1). The invention also improves the long-term circulation process of the anode electrode on the premise of ensuring the conventional performance (including short-term and long-term performance) of the lithium ion batteryThereby improving the long-term stability of the lithium ion battery.

Description

Cathode electrode and preparation method and application thereof

Technical Field

The invention belongs to the technical field of lithium ion batteries, and particularly relates to a cathode electrode and a preparation method and application thereof.

Background

As a core component of an electric vehicle, the cycle life of a power battery directly influences the service life of the whole vehicle and indirectly influences the development cost of the whole vehicle, the long-term cycle stability of the power battery is required to be designed and ensured at the initial development stage of the power battery, the long-term cycle stability of the power battery is in a crucial relation with the stability of an anode electrode, the irreversible consumption of active lithium of the anode electrode on the surface of an electrode particle is a main factor of the cycle attenuation of the power battery in the long-term cycle process of the power battery, and the irreversible consumption of the active lithium on the surface of the anode electrode particle in the cycle process is required to be inhibited in order to improve and optimize the long-.

Current methods to inhibit the irreversible consumption of active lithium at the surface of the anode electrode particles during cycling include the following two: (1) anode: surface functional group modification or surface coating is carried out, so that the surface stability of the particles is improved; (2) electrolyte aspect: adding a film forming additive. The technical defects of the existing technology for inhibiting the irreversible consumption of active lithium on the surface of anode electrode particles in the circulating process are analyzed as follows: (1) in the aspect of an anode: the surface functional group modification or surface coating of the particles can deteriorate the specific capacity of the particles, and the surface coating or functional group modification can reduce the compaction density, reduce the initial efficiency of the material, increase the consumption of active lithium at the initial stage and further deteriorate the energy density of a battery core. (2) Electrolyte aspect: the film forming additive is added, so that the thickness of the solid-phase electrolyte film on the surface is increased to a certain degree, and the surface structure of the anode electrode is stabilized to a certain degree, but on one hand, the solid-phase electrolyte film added by the film forming additive contains most organic substances, the instability of the solid-phase electrolyte film can be further decomposed in subsequent circulation, the consumption of the electrolyte is accelerated, and on the other hand, the film forming additive of the electrolyte can also be added at the cathode to form a film, so that the impedance of the cathode is increased.

Disclosure of Invention

The present invention is directed to solving, at least to some extent, one of the technical problems in the related art. Therefore, the invention aims to provide a cathode electrode and a preparation method and application thereof. On the premise of ensuring the conventional performance (including short-term and long-term performance) of the lithium ion battery, the stability of the anode electrode in the long-term circulation process is improved, so that the long-term stability of the lithium ion battery is improved.

In one aspect of the invention, the invention proposes a cathode electrode, according to an embodiment of the invention, comprising:

a cathode current collector;

a cathode active material layer coated on the cathode current collector,the cathode active material layer comprises a cathode active material, a binder, a conductive agent and a material capable of decomposing to generate CO under high-temperature formation₂The additive of (1).

According to the cathode electrode of the embodiment of the invention, the additive contained in the cathode active material layer is decomposed to generate CO under the dual actions of high temperature and high potential in the high temperature formation stage₂And transferred to the anode, the CO₂Preferentially reacts with trace moisture and active lithium formed in the charging and discharging process on the surface of the anode particles to generate Li₂CO₃、Li₂O, LiOH, and the like, to form a dense and stable inorganic solid electrolyte surface film on the surface of the anode particles. Then the electrolyte begins to decompose to generate an organic solid-phase electrolyte surface film which covers the surface of the inorganic solid-phase electrolyte surface film. CO generation by adding energy decomposition to the cathode active material layer₂Can increase the CO required for the interfacial film component of the solid-phase electrolyte₂The source of the electrolyte, the early reaction consumption of the electrolyte and the active lithium is reduced, the side reaction of the electrolyte solvent is reduced, and a large amount of CO is generated in the early stage₂The solid-phase electrolyte interface film formed on the surface of the anode is enabled to be more compact and stable, and the long-term reliability and stability of the subsequent battery cell are greatly improved. If the above additive is not added to the cathode active material layer, active lithium on the surface of the anode reacts with a solvent (EC/DEC/DMC/EMC/PC, etc.) in the electrolyte to generate CO₂And unstable organolithium compounds followed by CO₂Continuously reacting with active lithium to generate inorganic lithium compound, and continuously decomposing unstable organic lithium compound to generate CO₂、CH₄、C₂H₄And the like organic gases and stable organic compounds that do not continue to decompose.

Therefore, on the premise of ensuring the conventional performance (including short-term and long-term performance) of the lithium ion battery, the stability of the anode electrode in a long-term circulation process is improved, the long-term circulation performance such as the service life can be improved by 30-50%, and the power can be improved by 30-50%, so that the long-term stability of the lithium ion battery is improved. And meanwhile, the electrical properties of the battery cell, such as capacity, initial power and the like, are kept at the existing level and are not influenced, and the requirements of the existing power battery cell are met.

In addition, the cathode electrode according to the above embodiment of the present invention may further have the following additional technical features:

in some embodiments of the present invention, the additive is contained in an amount of 0 to 7% (more than 0), preferably 2 to 5%, of the total mass of the cathode active material layer. Therefore, the stability of the long-term circulation process of the anode electrode is improved, the additive is completely consumed in the formation stage, the gas production rate increase in the circulation stage caused by the residual additive is avoided, and the impedance increase power deterioration caused by the overlarge thickness of the anode solid-phase electrolyte membrane is avoided.

In some embodiments of the present invention, the cathode active material layer includes a plurality of layers, and the content of the additive in the plurality of layers of the cathode active material layer increases in a gradient in a direction away from the cathode current collector. Therefore, the situation that the additive in the outer cathode active material layer is completely consumed in the formation stage and the additive in the inner cathode active material layer is incompletely consumed is avoided, and the residual additive can cause the gas production in the circulation stage to be increased and the expansion force to be increased.

In some embodiments of the present invention, the innermost cathode active material layer is closest to the cathode current collector, the outermost cathode active material layer is farthest from the cathode current collector, and the additive content in the outermost cathode active material layer is 1% to 5%, preferably 2% to 4%; the content of the additive in the innermost cathode active material layer is 0 to 2%, preferably 0 to 1%. Therefore, the stability of the long-term circulation process of the anode electrode is improved, and meanwhile, the additives in the outer active material layer and the inner active material layer are completely consumed in the formation stage, so that the additive is prevented from being remained, and the thickness of the anode solid-phase electrolyte membrane is prevented from being too large.

In some embodiments of the present invention, the outermost cathode active material layer has a thickness of 10 to 100 micrometers; the thickness of the innermost cathode active material layer is 10 to 100 micrometers.

In some embodiments of the invention, the additive is a carbonate or/and an oxalate.

In some embodiments of the invention, the carbonate is selected from Li₂CO₃、Na₂CO₃And K₂CO₃At least one of (a).

In some embodiments of the invention, the oxalate salt is selected from Li₂C₂O₄/Na₂C₂O₄/K₂C₂O₄At least one of (a).

In some embodiments of the invention, the cathode active material is selected from the group consisting of LiNi_xCo_yMn_zFe_aAl_bP_cO₂Wherein x is more than or equal to 0 and less than or equal to 1, y is more than or equal to 0 and less than or equal to 1, z is more than or equal to 0 and less than or equal to 1, a is more than or equal to 0 and less than or equal to 1, b is more than or equal to 0 and less than or equal to 0.8, and c is more than or equal to 0 and less than.

In some embodiments of the invention, the binder is selected from at least one of polyvinylidene fluoride (PVDF), polyvinylidene fluoride, Polytetrafluoroethylene (PTFE), perfluoroethylene propylene copolymer (FEP), polyperfluoroalkoxy resin (PFA), Polychlorotrifluoroethylene (PCTFF), ethylene chlorotrifluoroethylene copolymer (ECTFE), ethylene tetrafluoroethylene copolymer (ETFE), and polyvinyl chloride (PVF).

In some embodiments of the invention, the conductive agent is selected from at least one of SP, CNTs, acetylene black, graphene, KS-6, and conductive polymers (polypyrrole, polyaniline, etc.).

In yet another aspect of the present invention, the present invention provides a method of preparing the above-described cathode electrode. According to an embodiment of the invention, the method comprises:

(1) decomposing the cathode active material, the binder, the conductive agent, the solvent and the solvent under high temperature to generate CO₂Mixing the additives of (a) to obtain a slurry;

(2) and coating the slurry on a cathode current collector, drying, rolling, die-cutting and punching to obtain the cathode pole piece.

According to the method for preparing the cathode electrode, the cathode electrode prepared by the method improves the stability of the anode electrode in the long-term circulation process on the premise of ensuring the conventional performance (including short-term and long-term performance) of the lithium ion battery, the long-term circulation performance such as the service life can be improved by 30-50%, and the power can be improved by 30-50%, so that the long-term stability of the lithium ion battery is improved. And meanwhile, the electrical properties of the battery cell, such as capacity, initial power and the like, are kept at the existing level and are not influenced, and the requirements of the existing power battery cell are met.

In a third aspect of the present invention, a lithium ion battery is presented. According to an embodiment of the present invention, the lithium ion battery has the cathode electrode described above or the cathode electrode prepared by the above method. Therefore, the long-term stability of the lithium ion battery is improved on the premise of ensuring the conventional performance (including short-term and long-term performance) of the lithium ion battery.

In a fourth aspect of the present invention, an electric vehicle is provided. According to an embodiment of the present invention, the electric vehicle has the lithium ion battery as described above. Therefore, the vehicle loaded with the lithium ion battery has excellent cruising ability, thereby meeting the use requirements of consumers.

Additional aspects and advantages of the invention will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the invention.

Drawings

The above and/or additional aspects and advantages of the present invention will become apparent and readily appreciated from the following description of the embodiments, taken in conjunction with the accompanying drawings of which:

fig. 1 is a schematic composition of an upper and lower structure of a double-layered electrode according to an embodiment of the present invention.

Detailed Description

Reference will now be made in detail to embodiments of the present invention, examples of which are illustrated in the accompanying drawings, wherein like or similar reference numerals refer to the same or similar elements or elements having the same or similar function throughout. The embodiments described below with reference to the drawings are illustrative and intended to be illustrative of the invention and are not to be construed as limiting the invention.

In one aspect of the invention, the invention proposes a cathode electrode, according to whichIn an embodiment, the cathode electrode includes: a cathode current collector; a cathode active material layer coated on the cathode current collector, the cathode active material layer including a cathode active material, a binder, a conductive agent, and being decomposed to generate CO at high temperature₂The additive of (1). The inventors have found that the additive contained in the cathode active material layer is decomposed to produce CO under the dual actions of high temperature and high potential at the high temperature formation stage₂And transferred to the anode, the CO₂Preferentially reacts with trace moisture and active lithium formed in the charging and discharging process on the surface of the anode particles to generate Li₂CO₃、Li₂O, LiOH, and the like, to form a dense and stable inorganic solid electrolyte surface film on the surface of the anode particles. Then the electrolyte begins to decompose to generate an organic solid-phase electrolyte surface film which covers the surface of the inorganic solid-phase electrolyte surface film. CO generation by adding energy decomposition to the cathode active material layer₂Can increase the CO required for the interfacial film component of the solid-phase electrolyte₂The source of the electrolyte, the early reaction consumption of the electrolyte and the active lithium is reduced, the side reaction of the electrolyte solvent is reduced, and a large amount of CO is generated in the early stage₂The solid-phase electrolyte interface film formed on the surface of the anode is enabled to be more compact and stable, and the long-term reliability and stability of the subsequent battery cell are greatly improved. If the above additive is not added to the cathode active material layer, active lithium on the surface of the anode reacts with a solvent (EC/DEC/DMC/EMC/PC, etc.) in the electrolyte to generate CO₂And unstable organolithium compounds followed by CO₂Continuously reacting with active lithium to generate inorganic lithium compound, and continuously decomposing unstable organic lithium compound to generate CO₂、CH₄、C₂H₄And the like organic gases and stable organic compounds that do not continue to decompose.

Therefore, on the premise of ensuring the conventional performance (including short-term and long-term performance) of the lithium ion battery, the stability of the anode electrode in a long-term circulation process is improved, the long-term circulation performance such as the service life can be improved by 30-50%, and the power can be improved by 30-50%, so that the long-term stability of the lithium ion battery is improved. And meanwhile, the electrical properties of the battery cell, such as capacity, initial power and the like, are kept at the existing level and are not influenced, and the requirements of the existing power battery cell are met.

Further, the additive is contained in an amount of 0 to 7% (more than 0), preferably 2 to 5%, of the total mass of the cathode active material layer. Therefore, the stability of the long-term circulation process of the anode electrode is improved, the additive is completely consumed in the formation stage, the gas production rate increase in the circulation stage caused by the residual additive is avoided, and the impedance increase power deterioration caused by the overlarge thickness of the anode solid-phase electrolyte membrane is avoided. The inventor finds that if the content of the cathode additive is too high, the additive cannot be completely consumed in the formation stage, and the residual additive can cause the gas production in the cycle stage to increase, the expansion force to increase and deteriorate the cycle performance of the lithium ion battery; on the other hand, if the content of the cathode additive is too large, the thickness of the anode solid phase electrolyte membrane is too large, and the impedance is increased, and the power is deteriorated.

Further, the cathode active material layer includes a plurality of layers in which the content of the additive increases in a gradient in a direction away from the cathode current collector. The inventors have found that the outer layer (the cathode active material layer far from the current collector) has a higher active material potential than the inner layer (the cathode active material layer near the current collector), and the outer layer reacts preferentially, so that the additive content in the outer cathode active material layer is relatively high, and the additive content in the inner layer is relatively low, thereby avoiding the situation that the additive in the outer cathode active material layer is completely consumed in the formation stage and the additive in the inner cathode active material layer is not completely consumed, and the residual additive will cause the gas production in the circulation stage to increase, resulting in the increase of the swelling force.

Further, the cathode active material layer closest to the cathode current collector is the innermost cathode active material layer, the cathode active material layer farthest from the cathode current collector is the outermost cathode active material layer, and the content of the additive in the outermost cathode active material layer is 1% -5%, preferably 2% -4%; the content of the additive in the innermost cathode active material layer is 0 to 2%, preferably 0 to 1%. Therefore, the stability of the long-term circulation process of the anode electrode is improved, and meanwhile, the additives in the outer active material layer and the inner active material layer are completely consumed in the formation stage, so that the additive is prevented from being remained, and the thickness of the anode solid-phase electrolyte membrane is prevented from being too large.

As a specific example, for visual display, fig. 1 shows a structural schematic diagram of an inner layer material system on a double-layer cathode electrode, in which active materials are the same material, where 1 is an aluminum foil current collector, 2 is an inner layer material system (the active material layer contains 1% of an additive), 3 is an outer layer material system (the active material layer contains 2% of an additive), 4 is active material particles, and 5 is additive particles. In practical application, the number of layers of the electrode can be adjusted according to practical situations, such as three-layer or four-layer electrodes, and the electrode materials with different number of layers can be one or different, the size and the shape of the particles can be the same or different, and the difference of the electrode material systems of different layers is only the content of the additive.

Further, the outermost cathode active material layer has a thickness of 10 to 100 μm; the thickness of the innermost cathode active material layer is 10 to 100 micrometers.

In the embodiment of the present invention, the kind of the additive is not particularly limited, and those skilled in the art can freely select the additive according to the actual situation as long as the additive can be decomposed to generate CO in the high temperature formation stage₂Namely, as a preferable mode, the additive is carbonate or/and oxalate. Further, the carbonate is selected from Li₂CO₃、Na₂CO₃And K₂CO₃At least one of; further, the oxalate salt is selected from Li₂C₂O₄/Na₂C₂O₄/K₂C₂O₄At least one of (a).

In the embodiment of the present invention, the kind of the cathode active material is not particularly limited, and may be arbitrarily selected by those skilled in the art according to practical circumstances, and as a preferable embodiment, the cathode active material is selected from the group consisting of LiNi_xCo_yMn_zFe_aAl_bP_cO₂At least one of which has a layered structure orThe material is olivine, wherein x is more than or equal to 0 and less than or equal to 1, y is more than or equal to 0 and less than or equal to 1, z is more than or equal to 0 and less than or equal to 1, a is more than or equal to 0 and less than or equal to 1, b is more than or equal to 0 and less than or equal to 0.8, and c is more than.

In the embodiment of the present invention, the kind of the above binder is not particularly limited, and may be arbitrarily selected by those skilled in the art according to practical circumstances, and as a preferable embodiment, the binder is selected from at least one of polyvinylidene fluoride (PVDF), polyvinylidene fluoride, Polytetrafluoroethylene (PTFE), perfluoroethylene propylene copolymer (FEP), polyperfluoroalkoxy resin (PFA), Polychlorotrifluoroethylene (PCTFF), ethylene-chlorotrifluoroethylene copolymer (ECTFE), ethylene-tetrafluoroethylene copolymer (ETFE), and polyvinyl chloride (PVF).

In the embodiment of the present invention, the kind of the above-mentioned conductive agent is not particularly limited, and may be arbitrarily selected by those skilled in the art according to actual circumstances, and as a preferable embodiment, the conductive agent is selected from at least one of SP, CNTs, acetylene black, graphene, KS-6, and conductive polymers (polypyrrole, polyaniline, and the like).

In yet another aspect of the present invention, the present invention provides a method of preparing the above-described cathode electrode. According to an embodiment of the invention, the method comprises:

s100: decomposing the cathode active material, the binder, the conductive agent, the solvent and the solvent under high temperature to generate CO₂To obtain a slurry.

S200: coating the slurry on a cathode current collector, drying, rolling, die cutting and punching to obtain a cathode pole piece

In the step, the slurry is coated on a cathode current collector, dried, rolled, die-cut and punched into a cathode pole piece. As a preferable scheme, the method comprises the steps of preparing slurry from additives with different contents, cathode active materials, binders and conductive agents, controlling the slurry with low additive content to be positioned in an inner layer, controlling the slurry with high additive content to be positioned in an outer layer, carrying out one-time coating by adopting multi-cavity coating or multi-die coating or carrying out multiple times of coating by adopting a single cavity or single die to realize the coating of the multilayer pole piece, and then realizing the multilayer pole piece with the additive content in gradient distribution by rolling, wherein the additive content in the electrode is gradually reduced from the outer layer of the pole piece to the inner layer of the pole piece.

In a third aspect of the present invention, a lithium ion battery is presented. According to an embodiment of the present invention, the lithium ion battery has the cathode electrode described above or the cathode electrode prepared by the above method. Therefore, the long-term stability of the lithium ion battery is improved on the premise of ensuring the conventional performance (including short-term and long-term performance) of the lithium ion battery.

The lithium ion battery with extremely high long-term cycling stability provided by the embodiment of the invention also comprises the following components: the anode is selected from graphite material (including natural graphite, artificial graphite, soft carbon, hard carbon, etc.) and alloy material Si/SiO₂Etc. can perform one or more of lithium intercalation and deintercalation materials; the separator is selected from one or more of PE, PP and non-woven fabric materials with high porosity and lithium ions allowed to freely pass through; the electrolyte comprises a solvent and a lithium salt, wherein the solvent is selected from one or more of cyclic esters such as EC and PC and linear esters such as DEC, DMC and EMC, and the lithium salt is selected from LiPF which can be effectively dissolved in the above esters₆、LiClO₄And LiBO₂And the like.

In a fourth aspect of the present invention, an electric vehicle is provided. According to an embodiment of the present invention, the electric vehicle has the lithium ion battery as described above. Therefore, the vehicle loaded with the lithium ion battery has excellent cruising ability, thereby meeting the use requirements of consumers.

The following embodiments of the present invention are described in detail, and it should be noted that the following embodiments are exemplary only, and are not to be construed as limiting the present invention. In addition, all reagents used in the following examples are commercially available or can be synthesized according to methods herein or known, and are readily available to those skilled in the art for reaction conditions not listed, if not explicitly stated.

Example 1

A double-layered cathode was prepared in which the additive content of the outer layer (cathode active material layer far from the current collector) was 1% and the additive content of the inner layer (cathode active material layer near the current collector) was 0%.

Taking cathode LiNi_0.5Co_0.2Mn_0.3O₂A ternary material, homogenized at a weight ratio of NCM (ternary material), PVDF (polyvinylidene fluoride), SP (conductive agent) of 95:3:2, wherein 1% of Li is contained₂CO₃And NMP (N methyl-2 pyrrolidone) is added to control the solid content to be 68-75%, and the viscosity is 6000-10000 mpa. After the stirring is completed, the slurry is introduced into the outer cavity.

Taking cathode LiNi_0.5Co_0.2Mn_0.3O₂The ternary material is homogenized according to the weight ratio of NCM (ternary material), PVDF (polyvinylidene fluoride) and SP (conductive agent) of 95:3:2, NMP (N-methyl-2 pyrrolidone) is added to control the solid content to be 68-75%, and the viscosity is 6000-10000 mpa-s. After the stirring is completed, the slurry is introduced into the inner cavity.

Then the outer cavity slurry and the inner cavity slurry are evenly coated on the surface of an aluminum foil substrate with the thickness of 12 mu m, and the coating weight of the two surfaces is 380g/m²The coating weight of the outer layer is controlled to be 190g/m by controlling the gasket of the upper inner cavity and the clamping degree²The inner layer coating weight was 190g/m²The weight distribution ratio of the upper inner layer to the lower inner layer is 5:5, and then the cathode pole piece is obtained by drying, rolling, die cutting and punching.

Example 2

Preparing a double-layer cathode, wherein the content of the additive in the outer layer is 2%, and the content of the additive in the inner layer is 0%.

Taking cathode LiNi_0.5Co_0.2Mn_0.3O₂A ternary material, homogenized at a weight ratio of NCM (ternary material), PVDF (polyvinylidene fluoride), SP (conductive agent) of 95:3:2, wherein 2% of Li is contained₂CO₃And NMP (N methyl-2 pyrrolidone) is added to control the solid content to be 68-75%, and the viscosity is 6000-10000 mpa. After the stirring is completed, the slurry is introduced into the outer cavity.

Taking cathode LiNi_0.5Co_0.2Mn_0.3O₂The ternary material is homogenized according to the weight ratio of NCM (ternary material), PVDF (polyvinylidene fluoride) and SP (conductive agent) of 95:3:2, NMP (N-methyl-2 pyrrolidone) is added to control the solid content to be 68-75%, and the viscosity is 6000-10000 mpa-s. Go toAfter stirring, the slurry is introduced into the inner cavity.

Then the outer cavity slurry and the inner cavity slurry are evenly coated on the surface of an aluminum foil substrate with the thickness of 12 mu m, and the coating weight of the two surfaces is 380g/m²The coating weight of the outer layer is controlled to be 190g/m by controlling the gasket of the upper inner cavity and the clamping degree²The inner layer coating weight was 190g/m²The weight distribution ratio of the upper inner layer to the lower inner layer is 5:5, and then the cathode pole piece is obtained by drying, rolling, die cutting and punching.

Example 3

A double-layer cathode was prepared, in which the content of the additive in the outer layer was 3% and the content of the additive in the inner layer was 0%.

Taking cathode LiNi_0.5Co_0.2Mn_0.3O₂A ternary material, homogenized at a weight ratio of NCM (ternary material), PVDF (polyvinylidene fluoride), SP (conductive agent) of 95:3:2, wherein 3% of Li is contained₂CO₃And NMP (N methyl-2 pyrrolidone) is added to control the solid content to be 68-75%, and the viscosity is 6000-10000 mpa. After the stirring is completed, the slurry is introduced into the outer cavity.

Taking cathode LiNi_0.5Co_0.2Mn_0.3O₂The ternary material is homogenized according to the weight ratio of NCM (ternary material), PVDF (polyvinylidene fluoride) and SP (conductive agent) of 95:3:2, NMP (N-methyl-2 pyrrolidone) is added to control the solid content to be 68-75%, and the viscosity is 6000-10000 mpa-s. After the stirring is completed, the slurry is introduced into the inner cavity.

Then the outer cavity slurry and the inner cavity slurry are evenly coated on the surface of an aluminum foil substrate with the thickness of 12 mu m, and the coating weight of the two surfaces is 380g/m²The coating weight of the outer layer is controlled to be 190g/m by controlling the gasket of the upper inner cavity and the clamping degree²The inner layer coating weight was 190g/m²The weight distribution ratio of the upper inner layer to the lower inner layer is 5:5, and then the cathode pole piece is obtained by drying, rolling, die cutting and punching.

Example 4

A double-layer cathode was prepared, in which the content of the additive in the outer layer was 4% and the content of the additive in the inner layer was 0%.

Taking cathode LiNi_0.5Co_0.2Mn_0.3O₂Ternary materials, based on NCM (ternary material), PVDF (polyvinylidene fluoride), SP (lead)Electrical agent) homogenization was performed at a weight ratio of 95:3:2, with 4% content of Li₂CO₃And NMP (N methyl-2 pyrrolidone) is added to control the solid content to be 68-75%, and the viscosity is 6000-10000 mpa. After the stirring is completed, the slurry is introduced into the outer cavity.

Taking cathode LiNi_0.5Co_0.2Mn_0.3O₂The ternary material is homogenized according to the weight ratio of NCM (ternary material), PVDF (polyvinylidene fluoride) and SP (conductive agent) of 95:3:2, NMP (N-methyl-2 pyrrolidone) is added to control the solid content to be 68-75%, and the viscosity is 6000-10000 mpa-s. After the stirring is completed, the slurry is introduced into the inner cavity.

Then the outer cavity slurry and the inner cavity slurry are evenly coated on the surface of an aluminum foil substrate with the thickness of 12 mu m, and the coating weight of the two surfaces is 380g/m²The coating weight of the outer layer is controlled to be 190g/m by controlling the gasket of the upper inner cavity and the clamping degree²The inner layer coating weight was 190g/m²The weight distribution ratio of the upper inner layer to the lower inner layer is 5:5, and then the cathode pole piece is obtained by drying, rolling, die cutting and punching.

Example 5

Preparing a double-layer cathode, wherein the content of the additive in the outer layer is 5%, and the content of the additive in the inner layer is 0%.

Taking cathode LiNi_0.5Co_0.2Mn_0.3O₂A ternary material, homogenized at a weight ratio of NCM (ternary material), PVDF (polyvinylidene fluoride), SP (conductive agent) of 95:3:2, wherein 5% of Li is contained₂CO₃And NMP (N methyl-2 pyrrolidone) is added to control the solid content to be 68-75%, and the viscosity is 6000-10000 mpa. After the stirring is completed, the slurry is introduced into the outer cavity.

Taking cathode LiNi_0.5Co_0.2Mn_0.3O₂The ternary material is homogenized according to the weight ratio of NCM (ternary material), PVDF (polyvinylidene fluoride) and SP (conductive agent) of 95:3:2, NMP (N-methyl-2 pyrrolidone) is added to control the solid content to be 68-75%, and the viscosity is 6000-10000 mpa-s. After the stirring is completed, the slurry is introduced into the inner cavity.

Then the outer cavity slurry and the inner cavity slurry are evenly coated on the surface of an aluminum foil substrate with the thickness of 12 mu m, and the coating weight of the two surfaces is 380g/m²By controlling the upper cavity gasket and the clamping degreeThe coating weight of the outer layer is 190g/m²The inner layer coating weight was 190g/m²The weight distribution ratio of the upper inner layer to the lower inner layer is 5:5, and then the cathode pole piece is obtained by drying, rolling, die cutting and punching.

Example 6

A double layer cathode was prepared with 1% additive on the outer layer and 1% additive on the inner layer.

Taking cathode LiNi_0.5Co_0.2Mn_0.3O₂The ternary material is homogenized according to the weight ratio of NCM (ternary material), PVDF (polyvinylidene fluoride) and SP (conductive agent) of 95:3:2, wherein 1% of Li2CO3 additive is added, NMP (N methyl-2 pyrrolidone) is added to control the solid content to be 68-75%, and the viscosity is 6000-. After the stirring is completed, the slurry is introduced into the outer cavity.

Taking cathode LiNi_0.5Co_0.2Mn_0.3O₂A ternary material, homogenized at a weight ratio of NCM (ternary material), PVDF (polyvinylidene fluoride), SP (conductive agent) of 95:3:2, wherein 1% of Li is contained₂CO₃And NMP (N methyl-2 pyrrolidone) is added to control the solid content to be 68-75%, and the viscosity is 6000-10000 mpa. After the stirring is completed, the slurry is introduced into the inner cavity.

Then the outer cavity slurry and the inner cavity slurry are evenly coated on the surface of an aluminum foil substrate with the thickness of 12 mu m, and the coating weight of the two surfaces is 380g/m²The coating weight of the outer layer is controlled to be 190g/m by controlling the gasket of the upper inner cavity and the clamping degree²The inner layer coating weight was 190g/m²The weight distribution ratio of the upper inner layer to the lower inner layer is 5:5, and then the cathode pole piece is obtained by drying, rolling, die cutting and punching.

Example 7

A double-layer cathode was prepared, in which the content of the additive in the outer layer was 2% and the content of the additive in the inner layer was 1%.

Taking cathode LiNi_0.5Co_0.2Mn_0.3O₂A ternary material, homogenized at a weight ratio of NCM (ternary material), PVDF (polyvinylidene fluoride), SP (conductive agent) of 95:3:2, wherein 2% of Li is contained₂CO₃And NMP (N methyl-2 pyrrolidone) is added to control the solid content to be 68-75%, and the viscosity is 6000-10000 mpa. After the stirring is finishedThe slurry is passed into the outer chamber.

Taking cathode LiNi_0.5Co_0.2Mn_0.3O₂A ternary material, homogenized at a weight ratio of NCM (ternary material), PVDF (polyvinylidene fluoride), SP (conductive agent) of 95:3:2, wherein 1% of Li is contained₂CO₃And NMP (N methyl-2 pyrrolidone) is added to control the solid content to be 68-75%, and the viscosity is 6000-10000 mpa. After the stirring is completed, the slurry is introduced into the inner cavity.

Then the outer cavity slurry and the inner cavity slurry are evenly coated on the surface of an aluminum foil substrate with the thickness of 12 mu m, and the coating weight of the two surfaces is 380g/m²The coating weight of the outer layer is controlled to be 190g/m by controlling the gasket of the upper inner cavity and the clamping degree²The inner layer coating weight was 190g/m²The weight distribution ratio of the upper inner layer to the lower inner layer is 5:5, and then the cathode pole piece is obtained by drying, rolling, die cutting and punching.

Example 8

A double-layer cathode was prepared, in which the content of the additive in the outer layer was 3% and the content of the additive in the inner layer was 1%.

Taking cathode LiNi_0.5Co_0.2Mn_0.3O₂A ternary material, homogenized at a weight ratio of NCM (ternary material), PVDF (polyvinylidene fluoride), SP (conductive agent) of 95:3:2, wherein 3% of Li is contained₂CO₃And NMP (N methyl-2 pyrrolidone) is added to control the solid content to be 68-75%, and the viscosity is 6000-10000 mpa. After the stirring is completed, the slurry is introduced into the outer cavity.

Taking cathode LiNi_0.5Co_0.2Mn_0.3O₂A ternary material, homogenized at a weight ratio of NCM (ternary material), PVDF (polyvinylidene fluoride), SP (conductive agent) of 95:3:2, wherein 1% of Li is contained₂CO₃And NMP (N methyl-2 pyrrolidone) is added to control the solid content to be 68-75%, and the viscosity is 6000-10000 mpa. After the stirring is completed, the slurry is introduced into the inner cavity.

Then the outer cavity slurry and the inner cavity slurry are evenly coated on the surface of an aluminum foil substrate with the thickness of 12 mu m, and the coating weight of the two surfaces is 380g/m²The coating weight of the outer layer is controlled to be 190g/m by controlling the gasket of the upper inner cavity and the clamping degree²The inner layer coating weight was 190g/m²The weight distribution ratio of the upper inner layer to the lower inner layer is 5:5, and then the cathode pole piece is obtained by drying, rolling, die cutting and punching.

Example 9

A double layer cathode was prepared with an outer layer additive content of 4% and an inner layer additive content of 1%.

Taking cathode LiNi_0.5Co_0.2Mn_0.3O₂A ternary material, homogenized in the weight ratio of NCM (ternary material), PVDF (polyvinylidene fluoride), SP (conductive agent) 95:3:2, with 4% Li₂CO₃And NMP (N methyl-2 pyrrolidone) is added to control the solid content to be 68-75%, and the viscosity is 6000-10000 mpa. After the stirring is completed, the slurry is introduced into the outer cavity.

Taking cathode LiNi_0.5Co_0.2Mn_0.3O₂A ternary material, homogenized at a weight ratio of NCM (ternary material), PVDF (polyvinylidene fluoride), SP (conductive agent) of 95:3:2, wherein 1% of Li is contained₂CO₃And NMP (N methyl-2 pyrrolidone) is added to control the solid content to be 68-75%, and the viscosity is 6000-10000 mpa. After the stirring is completed, the slurry is introduced into the inner cavity.

Then the outer cavity slurry and the inner cavity slurry are evenly coated on the surface of an aluminum foil substrate with the thickness of 12 mu m, and the coating weight of the two surfaces is 380g/m²The coating weight of the outer layer is controlled to be 190g/m by controlling the gasket of the upper inner cavity and the clamping degree²The inner layer coating weight was 190g/m²The weight distribution ratio of the upper inner layer to the lower inner layer is 5:5, and then the cathode pole piece is obtained by drying, rolling, die cutting and punching.

Example 10

A double-layer cathode was prepared, in which the content of the additive in the outer layer was 5% and the content of the additive in the inner layer was 1%.

Taking cathode LiNi_0.5Co_0.2Mn_0.3O₂A ternary material, homogenized at a weight ratio of NCM (ternary material), PVDF (polyvinylidene fluoride), SP (conductive agent) of 95:3:2, wherein 5% of Li is contained₂CO₃And NMP (N methyl-2 pyrrolidone) is added to control the solid content to be 68-75%, and the viscosity is 6000-10000 mpa. After the stirring is completed, the slurry is introduced into the outer cavity.

Taking cathode LiNi_0.5Co_0.2Mn_0.3O₂A ternary material, homogenized at a weight ratio of NCM (ternary material), PVDF (polyvinylidene fluoride), SP (conductive agent) of 95:3:2, wherein 1% of Li is contained₂CO₃And NMP (N methyl-2 pyrrolidone) is added to control the solid content to be 68-75%, and the viscosity is 6000-10000 mpa. After the stirring is completed, the slurry is introduced into the inner cavity.

Then the outer cavity slurry and the inner cavity slurry are evenly coated on the surface of an aluminum foil substrate with the thickness of 12 mu m, and the coating weight of the two surfaces is 380g/m²The coating weight of the outer layer is controlled to be 190g/m by controlling the gasket of the upper inner cavity and the clamping degree²The inner layer coating weight was 190g/m²The weight distribution ratio of the upper inner layer to the lower inner layer is 5:5, and then the cathode pole piece is obtained by drying, rolling, die cutting and punching.

Example 11

A double-layer cathode was prepared, in which the content of the additive in the outer layer was 1% and the content of the additive in the inner layer was 2%.

Taking cathode LiNi_0.5Co_0.2Mn_0.3O₂A ternary material, homogenized at a weight ratio of NCM (ternary material), PVDF (polyvinylidene fluoride), SP (conductive agent) of 95:3:2, wherein 1% of Li is contained₂CO₃And NMP (N methyl-2 pyrrolidone) is added to control the solid content to be 68-75%, and the viscosity is 6000-10000 mpa. After the stirring is completed, the slurry is introduced into the outer cavity.

Taking cathode LiNi_0.5Co_0.2Mn_0.3O₂A ternary material, homogenized at a weight ratio of NCM (ternary material), PVDF (polyvinylidene fluoride), SP (conductive agent) of 95:3:2, wherein 2% of Li is contained₂CO₃And NMP (N methyl-2 pyrrolidone) is added to control the solid content to be 68-75%, and the viscosity is 6000-10000 mpa. After the stirring is completed, the slurry is introduced into the inner cavity.

Then the outer cavity slurry and the inner cavity slurry are evenly coated on the surface of an aluminum foil substrate with the thickness of 12 mu m, and the coating weight of the two surfaces is 380g/m²The coating weight of the outer layer is controlled to be 190g/m by controlling the gasket of the upper inner cavity and the clamping degree²The inner layer coating weight was 190g/m²I.e. the weight distribution ratio of the upper inner layer to the lower inner layer is 5:5, thenAnd drying, rolling, die cutting and punching to obtain the cathode plate.

Example 12

A double layer cathode was prepared with an outer layer additive content of 2% and an inner layer additive content of 2%.

Taking cathode LiNi_0.5Co_0.2Mn_0.3O₂A ternary material, homogenized at a weight ratio of NCM (ternary material), PVDF (polyvinylidene fluoride), SP (conductive agent) of 95:3:2, wherein 2% of Li is contained₂CO₃And NMP (N methyl-2 pyrrolidone) is added to control the solid content to be 68-75%, and the viscosity is 6000-10000 mpa. After the stirring is completed, the slurry is introduced into the outer cavity.

Taking cathode LiNi_0.5Co_0.2Mn_0.3O₂A ternary material, homogenized at a weight ratio of NCM (ternary material), PVDF (polyvinylidene fluoride), SP (conductive agent) of 95:3:2, wherein 2% of Li is contained₂CO₃And NMP (N methyl-2 pyrrolidone) is added to control the solid content to be 68-75%, and the viscosity is 6000-10000 mpa. After the stirring is completed, the slurry is introduced into the inner cavity.

Then the outer cavity slurry and the inner cavity slurry are evenly coated on the surface of an aluminum foil substrate with the thickness of 12 mu m, and the coating weight of the two surfaces is 380g/m²The coating weight of the outer layer is controlled to be 190g/m by controlling the gasket of the upper inner cavity and the clamping degree²The inner layer coating weight was 190g/m²The weight distribution ratio of the upper inner layer to the lower inner layer is 5:5, and then the cathode pole piece is obtained by drying, rolling, die cutting and punching.

Example 13

A double-layer cathode was prepared, in which the content of the additive in the outer layer was 3% and the content of the additive in the inner layer was 2%.

Taking cathode LiNi_0.5Co_0.2Mn_0.3O₂A ternary material, homogenized at a weight ratio of NCM (ternary material), PVDF (polyvinylidene fluoride), SP (conductive agent) of 95:3:2, wherein 3% of Li is contained₂CO₃And NMP (N methyl-2 pyrrolidone) is added to control the solid content to be 68-75%, and the viscosity is 6000-10000 mpa. After the stirring is completed, the slurry is introduced into the outer cavity.

Taking cathode LiNi_0.5Co_0.2Mn_0.3O₂A ternary material, homogenized at a weight ratio of NCM (ternary material), PVDF (polyvinylidene fluoride), SP (conductive agent) of 95:3:2, wherein 2% of Li is contained₂CO₃And NMP (N methyl-2 pyrrolidone) is added to control the solid content to be 68-75%, and the viscosity is 6000-10000 mpa. After the stirring is completed, the slurry is introduced into the inner cavity.

Then the outer cavity slurry and the inner cavity slurry are evenly coated on the surface of an aluminum foil substrate with the thickness of 12 mu m, and the coating weight of the two surfaces is 380g/m²The coating weight of the outer layer is controlled to be 190g/m by controlling the gasket of the upper inner cavity and the clamping degree²The inner layer coating weight was 190g/m²The weight distribution ratio of the upper inner layer to the lower inner layer is 5:5, and then the cathode pole piece is obtained by drying, rolling, die cutting and punching.

Example 14

A double layer cathode was prepared with an outer layer additive content of 4% and an inner layer additive content of 2%.

Taking cathode LiNi_0.5Co_0.2Mn_0.3O₂The ternary material is homogenized according to the weight ratio of NCM (ternary material), PVDF (polyvinylidene fluoride) and SP (conductive agent) of 95:3:2, wherein 4% of Li2CO3 additive is added, NMP (N methyl-2 pyrrolidone) is added to control the solid content to be 68-75%, and the viscosity is 6000-. After the stirring is completed, the slurry is introduced into the outer cavity.

Taking cathode LiNi_0.5Co_0.2Mn_0.3O₂A ternary material, homogenized at a weight ratio of NCM (ternary material), PVDF (polyvinylidene fluoride), SP (conductive agent) of 95:3:2, wherein 2% of Li is contained₂CO₃And NMP (N methyl-2 pyrrolidone) is added to control the solid content to be 68-75%, and the viscosity is 6000-10000 mpa. After the stirring is completed, the slurry is introduced into the inner cavity.

Then the outer cavity slurry and the inner cavity slurry are evenly coated on the surface of an aluminum foil substrate with the thickness of 12 mu m, and the coating weight of the two surfaces is 380g/m²The coating weight of the outer layer is controlled to be 190g/m by controlling the gasket of the upper inner cavity and the clamping degree²The inner layer coating weight was 190g/m²The weight distribution ratio of the upper inner layer to the lower inner layer is 5:5, and then the cathode pole piece is obtained by drying, rolling, die cutting and punching.

Example 15

A double-layer cathode was prepared, in which the content of the additive in the outer layer was 5% and the content of the additive in the inner layer was 2%.

Taking cathode LiNi_0.5Co_0.2Mn_0.3O₂A ternary material, homogenized at a weight ratio of NCM (ternary material), PVDF (polyvinylidene fluoride), SP (conductive agent) of 95:3:2, wherein 5% of Li is contained₂CO₃And NMP (N methyl-2 pyrrolidone) is added to control the solid content to be 68-75%, and the viscosity is 6000-10000 mpa. After the stirring is completed, the slurry is introduced into the outer cavity.

Taking cathode LiNi_0.5Co_0.2Mn_0.3O₂A ternary material, homogenized at a weight ratio of NCM (ternary material), PVDF (polyvinylidene fluoride), SP (conductive agent) of 95:3:2, wherein 2% of Li is contained₂CO₃And NMP (N methyl-2 pyrrolidone) is added to control the solid content to be 68-75%, and the viscosity is 6000-10000 mpa. After the stirring is completed, the slurry is introduced into the inner cavity.

Then the outer cavity slurry and the inner cavity slurry are evenly coated on the surface of an aluminum foil substrate with the thickness of 12 mu m, and the coating weight of the two surfaces is 380g/m²The coating weight of the outer layer is controlled to be 190g/m by controlling the gasket of the upper inner cavity and the clamping degree²The inner layer coating weight was 190g/m²The weight distribution ratio of the upper inner layer to the lower inner layer is 5:5, and then the cathode pole piece is obtained by drying, rolling, die cutting and punching.

Example 16

A double-layer cathode was prepared, in which the content of the additive in the outer layer was 2% and the content of the additive in the inner layer was 1%.

Taking cathode LiNi_0.5Co_0.2Mn_0.3O₂A ternary material, homogenized at a weight ratio of NCM (ternary material), PVDF (polyvinylidene fluoride), SP (conductive agent) of 95:3:2, wherein 2% of Li is contained₂CO₃And NMP (N methyl-2 pyrrolidone) is added to control the solid content to be 68-75%, and the viscosity is 6000-10000 mpa. After the stirring is completed, the slurry is introduced into the outer cavity.

Taking cathode LiNi_0.5Co_0.2Mn_0.3O₂Ternary materials, in terms of NCM (ternary materials): PVDF (polyvinylidene fluoride)Vinyl fluoride SP (conductive agent) was homogenized at a weight ratio of 95:3:2, with 1% Li content₂CO₃And NMP (N methyl-2 pyrrolidone) is added to control the solid content to be 68-75%, and the viscosity is 6000-10000 mpa. After the stirring is completed, the slurry is introduced into the inner cavity.

Then the outer cavity slurry and the inner cavity slurry are evenly coated on the surface of an aluminum foil substrate with the thickness of 12 mu m, and the coating weight of the two surfaces is 380g/m²The coating weight of the outer layer is controlled to be 114g/m by controlling the gasket of the upper inner cavity and the clamping degree²The inner coating weight was 266g/m²Namely, the weight distribution ratio of the upper inner layer is 3:7, and then the cathode plate is obtained by drying, rolling, die cutting and punching.

Example 17

A double-layer cathode was prepared, in which the content of the additive in the outer layer was 2% and the content of the additive in the inner layer was 1%.

Taking cathode LiNi_0.5Co_0.2Mn_0.3O₂A ternary material, homogenized at a weight ratio of NCM (ternary material), PVDF (polyvinylidene fluoride), SP (conductive agent) of 95:3:2, wherein 2% of Li is contained₂CO₃And NMP (N methyl-2 pyrrolidone) is added to control the solid content to be 68-75%, and the viscosity is 6000-10000 mpa. After the stirring is completed, the slurry is introduced into the outer cavity.

Taking cathode LiNi_0.5Co_0.2Mn_0.3O₂A ternary material, homogenized at a weight ratio of NCM (ternary material), PVDF (polyvinylidene fluoride), SP (conductive agent) of 95:3:2, wherein 1% of Li is contained₂CO₃And NMP (N methyl-2 pyrrolidone) is added to control the solid content to be 68-75%, and the viscosity is 6000-10000 mpa. After the stirring is completed, the slurry is introduced into the inner cavity.

Then the outer cavity slurry and the inner cavity slurry are evenly coated on the surface of an aluminum foil substrate with the thickness of 12 mu m, and the coating weight of the two surfaces is 380g/m²The coating weight of the outer layer is controlled to be 266g/m by controlling the gasket of the upper inner cavity and the clamping degree²The inner layer coating weight was 114g/m²Namely, the weight distribution ratio of the upper inner layer is 7:4, and then the cathode pole piece is obtained by drying, rolling, die cutting and punching.

Comparative example 1

Single layer cathode (without additive)

Taking cathode LiNi_0.5Co_0.2Mn_0.3O₂The ternary material is homogenized according to the weight ratio of NCM (ternary material), PVDF (polyvinylidene fluoride) and SP (conductive agent) of 95:3:2, wherein NMP (N-methyl-2 pyrrolidone) is added to control the solid content to be 68-75%, and the viscosity is 6000-10000 mpa. After stirring, the cathode slurry was uniformly coated on the surface of a 12 μm aluminum foil substrate with a double-side coating weight of 380g/m²And then drying, rolling, die cutting and punching to obtain the cathode plate.

Anode electrode fabrication

Anode graphite, SBR (styrene butadiene rubber), CMC (sodium carboxymethylcellulose) and SP (conductive agent) are homogenized according to the weight ratio of 95:2.5:1.5:1, wherein water is added to control the solid content to be 45-55%, and the viscosity is 2000-4000mpa · s. After stirring, the anode slurry was uniformly coated on the surface of a copper foil substrate of 8 μm with a double-side coating weight of 180g/m²And then drying, rolling, die cutting and punching to obtain the anode plate.

Taking the cathode pole pieces and the anode pole pieces of the comparative example 1 and the examples 1-17, stacking the pole pieces layer by layer in the sequence of the diaphragm cathode diaphragm anode, manufacturing a naked battery cell, controlling the thickness of the comparative example to be consistent with that of the naked battery cell of the examples by controlling the number of cathode laminations, then putting the naked battery cell into a shell, baking, injecting liquid, forming, sealing and manufacturing the battery cell.

First, the cell capacity, internal resistance and weight of comparative example 1 and examples 1 to 17 were tested

And (3) at room temperature, taking three electric cores in the comparative example 1 and the examples 1-17, charging the electric cores to 4.2V at constant current and constant voltage according to the charging 0.33C by using a charging and discharging test cabinet, standing for 10min, discharging the electric cores to 2.8V according to the discharging 0.33C, and recording the discharging capacity.

The cell impedances of comparative example 1 and examples 1-17 were tested using a resistance tester and the values recorded.

The cell weights of comparative example 1 and examples 1-17 were measured using an electronic scale, and the cell weight energy density is discharge capacity discharge plateau voltage/cell weight.

TABLE 1 cell capacity, impedance, and energy density data for comparative example 1 and examples 1-17

From the cell capacity, impedance and energy density data of comparative example 1 and examples 1-17, it can be seen that Li was added to examples 1-17 relative to comparative example 1₂CO₃The additive causes the content proportion of the active substances of the electrode to be reduced, the energy density per unit weight of the active substances is reduced, the capacity is slightly reduced, and the reduction amplitude is increased along with the increase of the content of the additive; when the additive content exceeds a certain value, the capacity exertion is greatly reduced because the higher additive content reduces the content ratio of the active substances and deteriorates the capacity exertion. Under the condition of proper proportion of the upper layer and the lower layer, the capacity exertion has no obvious difference. Since only the electrode is added with Li₂CO₃The additive has no influence on the ohmic resistance.

Second, testing of cell cycle life and storage life testing comparative example 1 and examples 1-17

At room temperature, 2 cells of comparative example 1 and examples 1 to 17 were charged to 4.2V with a constant current and a constant voltage of 0.33C, left for 5min, and then discharged to 2.8V with 0.33C, and the discharge capacity was recorded, the capacity retention rate being the corresponding cycle discharge capacity/initial discharge capacity. The process is repeated until the capacity retention rate is less than or equal to 80 percent, and the number of the recording cycles is recorded.

And testing the gas production rate and the expansion force change condition in the circulation process by using a gas production tester and an expansion force testing device.

At room temperature, 2 cells of each of comparative example 1 and examples 1 to 17 were charged to 4.2V with a constant current and a constant voltage of 0.33C, and then the cells were placed in a high-temperature 45 ℃ incubator, stored for 500 days, and taken out every 30 days to test the capacity retention rate.

Table 2 comparative example 1 and examples 1-17 cell cycling and storage data

From the cycling and data storage of the cells of comparative example 1 and examples 1-17, it can be seen that Li was added in the examples₂CO₃Additives, which can improve the anode stability during the cycle life, and thus can improve the cycle performance; in addition, if the additive content exceeds a certain value, the cycle deterioration is caused because of a large amount of Li₂CO₃The thickness of the anode film is too large, the resistance is increased, and the remaining Li₂CO₃The gas production will continue to be decomposed during the circulation process, resulting in increased gas production and expansion force. In addition, under the condition that the contents of the integral electrode additives are consistent, the upper layer and the lower layer are distributed in a gradient manner, namely the upper layer (namely the outer layer) is high in content, and the lower layer (namely the inner layer) is low in content, so that the effect is superior to the design that the contents of the upper layer and the lower layer are the same, mainly the upper layer is relatively high in potential and will react preferentially, and the lower layer is relatively easy to remain. The proportion of different upper and lower layers is not obviously different, which shows that the proportion of the upper and lower layers in a proper range basically has no influence on the long-term cycle performance.

Third, testing the DC impedance and power of the whole life cycle of the cell of comparative example 1 and examples 1-17

At room temperature, 2 cells of comparative example and example BOL (at the initial state of circulation, capacity retention rate of 100%) are charged to 4.2V by using 0.33C constant current and constant voltage, and then discharged for 30min to 50% SOC by using 1C, discharged for 10S by using 4C current, and voltage values before and after discharge are recorded.

At room temperature, 2 cells of comparative example and example MOL (middle cycle state, capacity retention rate of 90%) are charged to 4.2V by using 0.33C constant current and constant voltage, then 1C is used for discharging for 30min to 50% SOC, 4C is used for discharging for 10S, and voltage values before and after discharging are recorded.

At room temperature, 2 cells of comparative example and example EOL (end of cycle state, capacity retention rate 80%) were charged to 4.2V with 0.33C constant current and constant voltage, and then discharged for 30min to 50% SOC with 1C, discharged for 10S with 4C current, and voltage values before and after discharge were recorded.

Discharge dc impedance (pre-discharge voltage-post-discharge voltage)/discharge current. Discharge power (pre-discharge voltage-lower limit voltage) lower limit voltage/discharge dc impedance.

Table 3 shows the DC impedance and power data for the entire life cycle of the cells of comparative example 1 and examples 1-17

From the direct current impedance and power data of the whole life cycle of the cell of comparative example 1 and examples 1-17, it can be seen that the cell impedance and power attenuation of the MOL and EOL states in the comparative example are very large, and the multilayer Li is adopted in the examples₂CO₃The additive electrode can greatly improve the impedance and power attenuation in the life cycle, and the multilayer electrode with the excessive additive content causes the excessive thickness of the formed film due to the fact that a large amount of additive generates gas in the initial state and reacts at the anode to form the film, so that the impedance and power in the initial state are inferior to those of a comparison group. The proportion of different upper and lower layers is not obviously different, which shows that the proper proportion of the upper and lower layers has no influence on the power maintenance.

In the description herein, references to the description of the term "one embodiment," "some embodiments," "an example," "a specific example," or "some examples," etc., mean that a particular feature, structure, material, or characteristic described in connection with the embodiment or example is included in at least one embodiment or example of the invention. In this specification, the schematic representations of the terms used above are not necessarily intended to refer to the same embodiment or example. Furthermore, the particular features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples. Furthermore, various embodiments or examples and features of different embodiments or examples described in this specification can be combined and combined by one skilled in the art without contradiction.

Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention, and that variations, modifications, substitutions and alterations can be made to the above embodiments by those of ordinary skill in the art within the scope of the present invention.

Claims (10)

1. A cathode electrode, comprising:

a cathode current collector;

a cathode active material layer coated on the cathode current collector, the cathode active material layer including a cathode active material, a binder, a conductive agent, and being decomposed to generate CO at high temperature₂The additive of (1).

2. The cathode electrode according to claim 1, wherein the additive is contained in an amount of 0 to 7%, preferably 2 to 5%, based on the total mass of the cathode active material layer.

3. The cathode electrode according to claim 1, wherein the cathode active material layer comprises a plurality of layers in which the content of the additive increases in a gradient in a direction away from the cathode current collector.

4. The cathode electrode according to claim 3, wherein the innermost cathode active material layer is closest to the cathode current collector, the outermost cathode active material layer is farthest from the cathode current collector, and the additive content in the outermost cathode active material layer is 1% to 5%, preferably 2% to 4%; the content of the additive in the innermost cathode active material layer is 0 to 2%, preferably 0 to 1%.

5. The cathode electrode according to claim 4, wherein the outermost cathode active material layer has a thickness of 10 to 100 μm;

the thickness of the innermost cathode active material layer is 10 to 100 micrometers.

6. The cathode electrode according to any one of claims 1 to 5, wherein the additive is a carbonate or/and an oxalate;

optionally, the carbonate is selected from Li₂CO₃、Na₂CO₃And K₂CO₃At least one of;

optionally, the oxalate salt is selected from Li₂C₂O₄/Na₂C₂O₄/K₂C₂O₄At least one of (a).

7. The cathode electrode according to any one of claims 1 to 5, wherein the cathode active material is selected from the group consisting of LiNi_xCo_yMn_zFe_aAl_bP_cO₂Wherein x is more than or equal to 0 and less than or equal to 1, y is more than or equal to 0 and less than or equal to 1, z is more than or equal to 0 and less than or equal to 1, a is more than or equal to 0 and less than or equal to 1, b is more than or equal to 0 and less than or equal to 0.8, and c is more than or equal to 0 and less than;

optionally, the binder is selected from at least one of polyvinylidene fluoride, polytetrafluoroethylene, perfluoroethylene propylene copolymer, polyperfluoroalkoxy resin, polychlorotrifluoroethylene, ethylene-chlorotrifluoroethylene copolymer, ethylene-tetrafluoroethylene copolymer, and polyvinyl chloride;

optionally, the conductive agent is selected from at least one of SP, CNTs, acetylene black, graphene, KS-6, and conductive polymers.

8. A method of making the cathode electrode of any one of claims 1 to 7, comprising:

(1) decomposing the cathode active material, the binder, the conductive agent, the solvent and the solvent under high temperature to generate CO₂Mixing the additives of (a) to obtain a slurry;

(2) and coating the slurry on a cathode current collector, drying, rolling, die-cutting and punching to obtain the cathode pole piece.

9. A lithium ion battery comprising the cathode electrode according to any one of claims 1 to 7.

10. An electric vehicle comprising the lithium ion battery according to claim 9.

Images