阅读说明：本技术 一种锂离子电池正极极片及其制备方法 (Lithium ion battery positive pole piece and preparation method thereof ) 是由 常武杰 段士涛 牛壮壮 张飞 于 2019-08-02 设计创作，主要内容包括：本发明公开了一种锂离子电池正极极片,包括集流体和涂覆在集流体上的涂层,所述涂层靠近所述集流体的部分导电剂的含量大于远离所述集流体部分导电剂的含量。本发明还公开了上述正极极片的制备方法,包括以下步骤：步骤一：分别制备底层浆料和上层浆料；其中,所述底层浆料中导电剂的含量大于所述上层浆料中导电剂的含量；步骤二：在所述集流体上涂布所述底层浆料,涂覆厚度2－10μm,烘干；步骤三：在烘干后的涂层上涂布所述上层浆料,烘干、辊压。本发明的正极片靠近集流体的部分导电剂含量大,其导电性较所述远离集流体部分大,从而提高了涂层中活性物质与集流体之间的导电性,减小了电池内阻,提高了电池的倍率性能和循环性能。(The invention discloses a positive pole piece of a lithium ion battery, which comprises a current collector and a coating coated on the current collector, wherein the content of a part of conductive agent of the coating, which is close to the current collector, is greater than that of a part of conductive agent far away from the current collector. The invention also discloses a preparation method of the positive pole piece, which comprises the following steps: the method comprises the following steps: respectively preparing bottom layer slurry and upper layer slurry; wherein the content of the conductive agent in the bottom layer slurry is greater than the content of the conductive agent in the upper layer slurry; step two: coating the bottom layer slurry on the current collector, wherein the coating thickness is 2-10 mu m, and drying; step three: and coating the upper slurry on the dried coating, drying and rolling. The part of the positive plate close to the current collector has high conductive agent content, and the conductivity of the positive plate is higher than that of the part far away from the current collector, so that the conductivity between an active substance in the coating and the current collector is improved, the internal resistance of the battery is reduced, and the rate capability and the cycle performance of the battery are improved.)

1. The positive pole piece of the lithium ion battery comprises a current collector and a coating coated on the current collector, and is characterized in that the content of a part of conductive agent, close to the current collector, of the coating is greater than that of a part of conductive agent, far away from the current collector.

2. The positive electrode sheet of the lithium ion battery of claim 1, wherein the coating comprises a bottom layer adjacent to the current collector and an upper layer distal from the current collector, wherein the amount of conductive agent in the bottom layer is greater than the amount of conductive agent in the upper layer.

3. The positive electrode plate of the lithium ion battery as claimed in claim 2, wherein the mass percentage of the conductive agent in the upper layer is not more than 5%, the mass percentage of the binder is not more than 5%, and the mass percentage of the positive active material is 90-99%.

4. The lithium ion battery positive electrode sheet according to claim 2, wherein the mass percentage of the conductive agent in the bottom layer is not less than 50%, the mass percentage of the binder is not less than 10%, and the mass percentage of the positive electrode active material is 10% -40%.

5. The positive electrode sheet of the lithium ion battery according to claim 4, wherein the thickness of the base layer is 2 to 10 μm.

6. The lithium ion battery positive electrode sheet according to claim 4, wherein the conductive agent is at least one of graphite, carbon black, acetylene black, graphene and carbon nanotubes; the binder is polyvinylidene fluoride; the positive active material is lithium iron phosphate.

7. The positive electrode plate of the lithium ion battery according to claim 2, wherein the current collector is a single-optical-surface aluminum foil, a double-optical-surface aluminum foil or a porous aluminum foil.

8. A method for preparing the positive pole piece of the lithium ion battery as claimed in one of claims 1 to 7, characterized by comprising the following steps:

the method comprises the following steps: respectively preparing bottom layer slurry and upper layer slurry; wherein the content of the conductive agent in the bottom layer slurry is greater than the content of the conductive agent in the upper layer slurry;

step two: coating the bottom layer slurry on the current collector, wherein the coating thickness is 2-10 mu m, and drying;

step three: and coating the upper slurry on the dried coating, drying and rolling.

9. The preparation method of the positive pole piece of the lithium ion battery as claimed in claim 8, wherein the mass percentage of the conductive agent in the upper layer slurry is not more than 5%, the mass percentage of the binder is not more than 5%, and the mass percentage of the positive active material is 90-99%.

10. The preparation method of the positive pole piece of the lithium ion battery as claimed in claim 8, wherein the mass percentage of the conductive agent in the bottom layer slurry is not less than 50%, the mass percentage of the binder is not less than 10%, and the mass percentage of the positive active material is 10% -40%.

Technical Field

The invention belongs to the field of lithium ion batteries, and relates to a lithium ion battery positive pole piece and a preparation method thereof.

Background

Along with the increasing exhaustion of petrochemical energy and the increasing greenhouse effect, people are continuously searching for a novel environment-friendly new energy source which can slow down the energy crisis and avoid environmental pollution, and in the process, the lithium ion battery is in due charge and develops greatly. At present, the lithium ion battery is widely applied to the fields of digital products, electric automobiles and the like. The lithium ion battery mainly comprises a positive plate, a negative plate, a diaphragm and electrolyte. The positive pole piece is formed by coating positive pole slurry on a positive pole current collector, the coating mode of the positive pole slurry in the prior art is generally finished by coating the slurry with a certain proportion on an aluminum foil at one time, and the positive pole piece manufactured by the mode has poor conductivity and influences the rate capability, capacity and cycle performance of the battery.

Disclosure of Invention

The invention aims to provide a lithium ion battery positive pole piece with good conductivity, and the lithium ion battery manufactured by using the positive pole piece has good rate performance, capacity and cycle performance.

The technical scheme of the invention is as follows:

the positive pole piece of the lithium ion battery comprises a current collector and a coating coated on the current collector, wherein the content of partial conductive agent of the coating, which is close to the current collector, is greater than that of partial conductive agent far away from the current collector.

Preferably, the coating comprises a bottom layer close to the current collector and an upper layer far away from the current collector, wherein the content of the conductive agent in the bottom layer is greater than the content of the conductive agent in the upper layer.

Preferably, the mass percentage of the conductive agent in the upper layer is not more than 5%, the mass percentage of the binder is not more than 5%, and the mass percentage of the positive electrode active substance is 90-99%.

Preferably, the mass percentage of the conductive agent in the bottom layer is not less than 50%, the mass percentage of the binder is not less than 10%, and the mass percentage of the positive electrode active substance is 10% -40%.

Preferably, the thickness of the bottom layer is 2-10 μm.

Preferably, the conductive agent is at least one of graphite, carbon black, acetylene black, graphene and carbon nanotubes; the binder is polyvinylidene fluoride; the positive active material is lithium iron phosphate.

Preferably, the current collector is a single-optical-surface aluminum foil, a double-optical-surface aluminum foil or a porous aluminum foil.

The invention also aims to provide a preparation method of the lithium ion battery positive pole piece, which comprises the following steps:

the method comprises the following steps: respectively preparing bottom layer slurry and upper layer slurry; wherein the content of the conductive agent in the bottom layer slurry is greater than the content of the conductive agent in the upper layer slurry; step two: coating the bottom layer slurry on the current collector, wherein the coating thickness is 2-10 mu m, and drying; step three: and coating the upper slurry on the dried coating, drying and rolling.

Preferably, in the upper layer slurry: the mass percentage of the conductive agent is not more than 5%, the mass percentage of the binder is not more than 5%, and the mass percentage of the positive active substance is 90% -99%.

Preferably, in the primer slurry: the mass percentage of the conductive agent is not less than 50%, the mass percentage of the binder is not less than 10%, and the mass percentage of the positive electrode active substance is 10% -40%.

The invention has the beneficial effects that:

according to the invention, the bottom layer slurry and the upper layer slurry are prepared respectively, so that the content of the conductive agent in the bottom layer slurry is larger than that of the conductive agent in the upper layer slurry, and then the conductive agents are sequentially coated on the current collector, so that the content of the conductive agent of the part, close to the current collector, of the coating of the prepared positive pole piece is larger than that of the conductive agent of the part, far away from the current collector, of the coating of the prepared positive pole piece. The positive plate has higher conductivity than the part far from the current collector due to the high content of the conductive agent at the part close to the current collector, so that the conductivity between the active substance in the coating and the current collector is greatly improved, the internal resistance of the battery is reduced, and the rate capability and the cycle performance of the battery are improved.

Drawings

Fig. 1 is a graph showing 500 cycles of charge and discharge of the batteries manufactured in example 1 and comparative example.

Detailed Description

The present invention will be described in detail with reference to examples. It should be noted that the description of the embodiments is provided to help understanding of the present invention, but the present invention is not limited thereto. In addition, the technical features involved in the embodiments of the present invention described below may be combined with each other as long as they do not conflict with each other.