阅读说明：本技术 锂离子电池用隔膜及快充型锂离子电池的制备方法 (Diaphragm for lithium ion battery and preparation method of quick-charging type lithium ion battery ) 是由 孟宪慧 黄渭 徐永刚 赵卫军 于 2020-12-24 设计创作，主要内容包括：本发明涉及一种采用含有特殊结构的隔膜的快充型锂离子电池的制备方法。本发明的锂离子电池用隔膜包括隔膜基体以及位于隔膜基体一侧表面的连续的石墨层,石墨层具有多个间隔设置的岛状结构,石墨层包括粘结剂和石墨颗粒,石墨颗粒的粒径分布为D50在1-8μm之间。本发明的快充型锂离子电池在制备时,将上述特殊结构隔膜具有石墨层一面与负极极片贴合,并在一定的压力和温度下对制备后电芯进行热压复合,以使得负极极片与隔膜复合。本发明的技术直接可以在现有工艺产出的极片上通过简单的热压复合工艺达到与双层涂布工艺同样的效果,对生产产能和加工成本无影响。(The invention relates to a preparation method of a quick-charging lithium ion battery adopting a diaphragm with a special structure. The diaphragm for the lithium ion battery comprises a diaphragm substrate and a continuous graphite layer positioned on one side surface of the diaphragm substrate, wherein the graphite layer is provided with a plurality of island-shaped structures arranged at intervals, the graphite layer comprises a binder and graphite particles, and the particle size distribution of the graphite particles is D50 between 1 and 8 mu m. When the quick-charging lithium ion battery is prepared, one surface of the diaphragm with the special structure, which is provided with the graphite layer, is attached to the negative pole piece, and the prepared battery core is subjected to hot-pressing compounding at certain pressure and temperature, so that the negative pole piece and the diaphragm are compounded. The technology of the invention can directly achieve the same effect as a double-layer coating process on the pole piece produced by the prior process through a simple hot-pressing composite process, and has no influence on the production capacity and the processing cost.)

1. A separator for a lithium ion battery, characterized in that: the diaphragm comprises a diaphragm base body and a continuous graphite layer positioned on the surface of the diaphragm base body, wherein the graphite layer has a plurality of island-shaped structures arranged at intervals, the graphite layer comprises a binder and graphite particles, and the particle size distribution of the graphite particles is D50 and is between 1 and 8 mu m.

2. The separator for a lithium ion battery according to claim 1, wherein: the thickness of the graphite layer is 4-20 μm.

3. The separator for a lithium ion battery according to claim 1, wherein: the binder accounts for 1-5% of the total weight of the graphite layer, and the graphite particles account for 95-99% of the total weight of the graphite layer.

4. The separator for a lithium ion battery according to claim 1, wherein: the binder comprises one or more of PVDF, CMC/SBR, PAA and PVA.

5. The separator for a lithium ion battery according to claim 1, wherein: the graphite layer also comprises a conductive agent, wherein the conductive agent accounts for less than 5% of the total weight of the graphite layer.

6. The separator for a lithium ion battery according to claim 1, wherein: the material of the diaphragm substrate is selected from one or more of PE, PP and PI.

7. A preparation method of a quick-charging type lithium ion battery is characterized by comprising the following steps:

(1) preparing the separator for a lithium ion battery according to any one of claims 1 to 6;

(2) attaching the graphite layer of the diaphragm for the lithium ion battery to a negative pole piece at 1-20ton/mm²And carrying out hot-pressing compounding at the temperature of 70-95 ℃ under pressure so as to enable the negative pole piece and the diaphragm to be tightly compounded.

8. The method of claim 7, wherein: the negative pole piece comprises a negative active material, and the negative active material is attached to the graphite layer.

9. The method of claim 8, wherein: the negative active material comprises one or more of graphite, silicon carbon and LTO.

10. The method of claim 9, wherein: the particle diameter of the graphite in the negative electrode active material is larger than the average particle diameter of the graphite particles used for the coating layer.

Technical Field

The invention relates to the technical field of lithium ion batteries, in particular to a diaphragm for a lithium ion battery and a preparation method of a quick-charging type lithium ion battery.

Background

In order to improve the quick charge performance of the ion battery, improvement has been mainly made in terms of a negative electrode containing graphite. In addition, at present, the surface of the fast-charging electrode often generates a lithium separation phenomenon, and the main reason of the lithium separation is Li due to polarization under the condition of high multiplying power⁺The graphite layer can not be rapidly embedded, so that the lithium precipitation phenomenon is easy to occur on the surface of the negative pole piece. The dynamic performance can be improved by reducing the particle size of graphite and increasing the content of amorphous carbon on the surface, thereby reducing polarization and achieving the improvement of rate capability. However, such power type graphite has the disadvantages of low first efficiency and low gram capacity. Therefore, the energy density is lowered by using such a negative electrode entirely.

In order to overcome the problems, the conventional method generally adopts a double-layer coating method to prepare a negative electrode, wherein the bottom layer is coated with large-particle graphite, and the surface layer is coated with power type graphite. However, when the double-layer coating technology is adopted, a special coating die head needs to be customized, the manufacturing cost is high, and the requirements on the process parameters of coating are strict. If the coating speed needs to be strictly controlled, the processing temperature range is narrow, the switching between different graphite particles is difficult, and the like. The defects reduce the production capacity and improve the processing cost.

Disclosure of Invention

In order to solve the technical problems, the invention aims to provide a diaphragm for a lithium ion battery and a preparation method of a quick-charging lithium ion battery.

The first object of the invention is to provide a diaphragm for a lithium ion battery, which comprises a diaphragm substrate and a continuous graphite layer arranged on one side surface of the diaphragm substrate, wherein the graphite layer has a plurality of island-shaped structures arranged at intervals, the graphite layer comprises a binder and graphite particles, and the particle size distribution of the graphite particles is D50 and is between 1 and 8 mu m.

Preferably, the distribution of graphite particles is between D502-5 μm.

Further, the thickness of the graphite layer is 4 to 20 μm, and when the graphite particle size distribution D50 is 3 μm, the optimum thickness is 6 μm. The graphite particles can be sprayed on the surface of the diaphragm substrate by adopting a spraying mode.

Furthermore, the binder accounts for 1-5% of the total weight of the graphite layer, and the graphite particles account for 95-99% of the total weight of the graphite layer. In the graphite layer, graphite particles are uniformly distributed in the binder.

Further, the binder comprises one or more of PVDF (polytetrafluoroethylene), CMC/SBR (sodium carboxymethyl cellulose/styrene butadiene rubber), PAA (poly propionic acid) and PVA. Preferably, the binder is PVDF.

Furthermore, the lithium ion battery separator can also comprise a conductive agent, and the conductive agent accounts for less than 5% of the total weight of the graphite layer.

Further, the conductive agent is selected from carbon black, carbon nanotubes, graphene, and the like.

Furthermore, the lithium ion battery diaphragm also comprises a dispersing auxiliary agent, and the dispersing auxiliary agent accounts for less than 2% of the total weight of the graphite layer.

Further, PVA (polyvinyl alcohol) is used as the dispersion aid.

Further, the material of the diaphragm substrate is selected from one or more of PE, PP and PI.

Further, the thickness of the diaphragm substrate is 5-20 microns.

The second purpose of the invention is to provide a preparation method of a quick-charging lithium ion battery, which comprises the following steps:

(1) preparing the diaphragm for the lithium ion battery;

(2) attaching a graphite layer of a diaphragm for a lithium ion battery to a negative pole piece, and selecting proper pressure (1-20 ton/mm) according to the content of a binder in the graphite layer, the diaphragm material and the requirements of different hot-pressed stripping forces²) And hot-pressing and compounding under the pressure and at the temperature of 70-95 ℃ to compound the negative pole piece and the diaphragm.

Further, in the step (2), the negative electrode plate includes a negative electrode active material, and the negative electrode active material is attached to the graphite layer.

Further, the negative electrode active material is selected from a single graphite-containing material or a composite system containing silicon carbon, LTO and the like.

Further, the negative electrode active material is graphite, and the particle size of the graphite is larger than the particle size of the graphite particles in the coating layer. In general, the particle size of the graphite selected for the negative electrode active material is 10 to 30 μm. The process of the invention can achieve the structure that the negative pole piece has the tightly combined double-layer graphite material.

The invention coats a small particle of graphite material on the negative electrode surface of the diaphragm, thereby maintaining a certain energy density of the battery and improving the multiplying power and the cycle performance of the battery.

At the normal temperature of 25 ℃, the rechargeable battery with the SOC 0% -SOC 80% within 48 minutes or the charging rate of more than 1C is generally regarded as a quick-charging lithium ion battery.

By the scheme, the invention at least has the following advantages:

the diaphragm for the lithium ion battery adopts the graphite layer containing the small-particle functional graphite particles, fully utilizes the advantage of ultrahigh multiplying power of the small-particle graphite particles, greatly improves the phenomenon of lithium precipitation on the surface of the quick-charge electrode, and improves the cycle, multiplying power performance and safety performance of the quick-charge lithium ion battery.

In the preparation process of the quick-charging lithium ion battery, the diaphragm and the negative pole piece for the lithium ion battery are compounded by adopting a hot-pressing compounding process, so that the effect of negative double-layer coating that small-particle power graphite particles on the diaphragm are tightly combined with negative active matters on the original negative pole piece is achieved, and the quick-charging lithium ion battery with ultrahigh power performance is prepared. The method of combining the diaphragm and the hot-pressing composite process realizes the double-layer coating effect, and has the advantages of simple coating process, uniform coating and high operability compared with the original graphite coating process for coating double layers on the surface of the negative electrode at the same time and with different particle sizes. Meanwhile, the effect of tight combination of the diaphragm and the negative pole piece is achieved, so that the dynamics is improved from two aspects, and the power performance of the quick-charging lithium ion battery is greatly improved.

The foregoing description is only an overview of the technical solutions of the present invention, and in order to make the technical solutions of the present invention more clearly understood and to implement them in accordance with the contents of the description, the following description is made with reference to the preferred embodiments of the present invention and the accompanying detailed drawings.

Drawings

FIG. 1 is a schematic illustration of the attachment of a separator containing a layer of small-grained graphite to a negative electrode;

description of reference numerals:

1-a separator substrate; 2-power type graphite material; 3-large-particle artificial graphite; 4-copper foil.

Detailed Description

The following examples are given to further illustrate the embodiments of the present invention. The following examples are intended to illustrate the invention but are not intended to limit the scope of the invention.

Comparative example 1

A commercial 20 μm thick material is a PPPP separator.

Example 1

A diaphragm containing a small-particle graphite layer is prepared by the following steps:

specifically, selecting the power type graphite material 2, namely graphite a: d50 is 3 μm, the particle size distribution is 1-5 μm, and PVDF and water are prepared into solution. The surface of the diaphragm substrate 1 with the thickness of 20 microns is uniformly sprayed by adopting a spraying mode so as to form a continuous graphite layer on one side surface of the diaphragm substrate 1, and the graphite layer is provided with a plurality of island-shaped structures which are distributed at intervals. Wherein, in the graphite layer, the mass fractions of the power type graphite material 2 and PVDF in the total mass of the graphite layer are 95% and 5% in sequence. The diaphragm substrate 1 is made of a PP diaphragm, and the thickness of the graphite layer is 8 mu m.

Examples 2 to 6

A diaphragm containing a small-particle graphite layer is prepared by the following steps:

preparing a power type graphite material (graphite a: D50 is 3 mu m, the particle size distribution is 1-5 mu m or graphite b: D50 is 6 mu m, the particle size distribution is 2-10 mu m), PVDF, a conductive agent SuperP and water into a solution a or a solution b, and uniformly spraying the solution a or the solution b on the surface of a diaphragm with the thickness of 20 mu m by adopting a spraying mode so as to form a continuous graphite layer on one side surface of the diaphragm, wherein the graphite layer is provided with a plurality of island-shaped structures which are distributed at intervals. Wherein, in the graphite layer, the mass fractions of the power type graphite material, PVDF and the conductive agent in the total mass of the graphite layer are 95%, 3% and 2% in sequence. The diaphragm material is the PP diaphragm. The thickness of the graphite layer is shown in table 1.

TABLE 1 separator coating thickness and corresponding cathode table

The diaphragm of the embodiment is used for preparing the quick-charging lithium ion battery, and the steps are as follows:

by adopting the design of a 1Ah soft package battery, the anode material is a ternary 622 material, the cathode comprises a copper foil 4 and a cathode active layer positioned on one side surface of the copper foil 4, wherein the cathode active layer comprises large-particle artificial graphite 3 (the particle size is D5015 microns).

And the lithium ion battery is assembled by using the diaphragm of the comparative example 1 according to a conventional method.

In the lamination process, one surface of the diaphragm substrate 1 with the graphite layer is tightly attached to the negative active layer (figure 1), and then the hot pressing forming process is adopted, and 8 tons/mm of pressure is applied²Heating at 80 deg.C for 60 s to combine the diaphragm matrix 1 with the negative electrode tightly, thereby achieving double-layer coating effect.

The normal temperature cycle life of the lithium ion battery prepared above was tested. The cycle performance shows the improvement of the quick charge performance of the lithium ion battery by comparing the cycle life of two different charges under the same discharge condition (CC 1C-2.5V).

The first charging mode is as follows: charging: CC/CV 0.5C to 4.3V, 0.05C cut-off, SOC 0-80% charging time 96 min.

And a second charging mode: quick charging: 2C, 9min-1.5C, 8min-1C, 18min-0.5C to 4.3V, 0.05C cut-off, SOC 0-80% charging time 35 min. The results are shown in table 2:

TABLE 2 Electrical Properties of different lithium ion batteries

As can be seen from table 2, in examples 1 to 6, compared with comparative example 1, the improvement on normal-temperature normal charging is not obvious, the fast-charging cycle performance is remarkably improved, and the performance is improved by adding the conductive agent (examples 1 and 3). Further, the effect of graphite size and coating thickness was analyzed as follows:

(1) thickness of graphite layer

Graphite a: when D50 is 3 μm and the particle size distribution is 2 to 10 μm, the electrical properties of the lithium ion battery are improved and then reduced in comparative examples 2 to 4 with the increase in coating thickness (4 μm, 8 μm, 20 μm). The best performance is achieved when the thickness is 8 μm, i.e. the graphite layer thickness is about 2.5 times the value of D50 for graphite a (3 × 2.5 — 8.5 μm).

B, graphite b: d50 is 6 μm, and when the particle size distribution is 2-10 μm, the thinner the coating thickness is, the better the battery performance is.

(2) Influence of graphite particle size

Comparing example 4 with example 6, the electrical properties of the small particle graphite selected in the coating are better than those of the large particle graphite selected in the coating at the same thickness of 20 μm.

In order to improve the rate capability of a high-energy density quick-charging system, the prior art is a double-layer coating process. The invention develops a technology for coating a power type graphite material on the surface of a diaphragm, fully utilizes the good power of the graphite with small particle size, inhibits the high-rate lithium precipitation performance, greatly expands the performance window of charging under high rate, further reduces the charging time and maintains the excellent cycle performance. Meanwhile, the method has the characteristics of simple process and high manufacturability.

The above is only a preferred embodiment of the present invention, and is not intended to limit the present invention, it should be noted that, for those skilled in the art, many modifications and variations can be made without departing from the technical principle of the present invention, and these modifications and variations should also be regarded as the protection scope of the present invention.