CN217641407U

CN217641407U - Low-expansion silicon-carbon cathode and lithium ion battery thereof

Info

Publication number: CN217641407U
Application number: CN202220230746.1U
Authority: CN
Inventors: 杨春乐; 张越超; 高秀玲
Original assignee: Tianjin EV Energies Co Ltd
Current assignee: Tianjin EV Energies Co Ltd
Priority date: 2022-01-27
Filing date: 2022-01-27
Publication date: 2022-10-21
Anticipated expiration: 2032-01-27

Abstract

The utility model provides a silicon carbon negative pole of low inflation and lithium ion battery thereof, including the mass flow body and by interior and coat in proper order in the multilayer silicon carbon layer on the mass flow body outward, the expansion ratio on different silicon carbon layers by interior and outer reduces in proper order. Low expanded silicon carbon negative pole and lithium ion battery thereof set up two at least layers of silicon carbon layer outside the current collector, the outer lower silicon carbon electrode material of expansion rate that uses, the higher silicon carbon electrode material of expansion rate is used to the inlayer, through the outer constraint effect to the inlayer, can restrain the inflation on silicon carbon electrode surface, prevent to take place to break, the pulverization, reduction battery capacity decay rate.

Description

Low-expansion silicon-carbon cathode and lithium ion battery thereof

Technical Field

The utility model belongs to lithium ion battery accessory field especially relates to a low expanded silicon carbon negative pole and lithium ion battery thereof.

Background

With the continuous improvement of the requirement on energy density, the graphite cathode material is restricted by the theoretical capacity of 372mAh/g, the compaction density is improved for several years and basically reaches the limit, the silicon-carbon cathode material becomes a cathode material with the requirement on high energy density, and the theoretical capacity of silicon can reach 4200mAh/g.

But the binding force of the surface of the silicon-carbon negative plate is very small, so that the silicon on the surface of the plate or close to the surface expands very seriously to generate serious cracks, the silicon-carbon expansion causes the gap area among active particles of the negative electrode to be reduced or completely separated, and an electronic conductive network is damaged; at the same time, the cracks consume active lithium, causing rapid decay in battery capacity.

SUMMERY OF THE UTILITY MODEL

In view of this, the utility model aims at providing a low expanded silicon carbon negative pole and lithium ion battery thereof to solve silicon carbon electrode surface serious inflation, lead to the problem that negative pole conductivity descends, the capacity attenuates fast.

In order to achieve the above purpose, the technical scheme of the utility model is realized as follows:

the utility model provides a low expanded silicon carbon negative pole, includes the mass flow body and from interior to exterior in proper order the multilayer silicon carbon layer of coating on the mass flow body, the expansion ratio of different silicon carbon layers reduces from interior to exterior in proper order, plays the constraint effect through the outer silicon carbon layer that has low expansion ratio to the inlayer silicon carbon layer that has high expansion ratio, suppresses the inflation of silicon carbon negative pole.

Furthermore, the current collector is copper foil, and the thickness of the current collector is 5-10 μm.

Further, the double-sided surface density of the silicon-carbon layer of the innermost layer is 15mg/cm ² 。

Further, the double-sided surface density of the outermost silicon-carbon layer is 3mg/cm ² 。

Further, the silicon-carbon layer of the innermost layer comprises, by mass, 5% -30% of silicon-carbon, 65% -92.5% of graphite, 0.5% -5% of a conductive agent and 2% -5% of a binder.

Further, the outermost silicon-carbon layer comprises, by mass, 0% -10% of silicon-carbon, 74.5% -95% of graphite, 0.5% -10% of a conductive agent, and 2% -10% of a binder.

Further, in order to improve the binding effect of the surface layer on the silicon carbon of the lower layer, the binder used for the silicon carbon layer of the outermost layer comprises PAA, PAN or PEO crosslinking resin.

A lithium ion battery using the silicon-carbon cathode.

Compared with the prior art, low expanded silicon carbon negative pole and lithium ion battery thereof have following advantage:

low expanded silicon carbon negative pole and lithium ion battery thereof set up two at least layers of silicon carbon layer outside the current collector, the outer lower silicon carbon electrode material of expansion rate that uses, the higher silicon carbon electrode material of expansion rate is used to the inlayer, through the outer constraint effect to the inlayer, can restrain the inflation on silicon carbon electrode surface, prevent to take place to break, the pulverization, reduction battery capacity decay rate.

Drawings

The accompanying drawings, which form a part of the present disclosure, are included to provide a further understanding of the present disclosure, and are incorporated in and constitute a part of this specification, illustrate embodiments of the present disclosure and together with the description serve to explain the present disclosure. In the drawings:

fig. 1 is a schematic structural diagram of a silicon-carbon negative electrode according to an embodiment of the present invention.

Description of the reference numerals:

1. copper foil; 2. an inner silicon carbon layer; 3. a surface silicon carbon layer.

Detailed Description

It should be noted that, in the case of no conflict, the embodiments and features of the embodiments of the present invention may be combined with each other.

In the description of the present invention, it is to be understood that the terms "center", "longitudinal", "lateral", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc. indicate orientations or positional relationships based on the orientations or positional relationships shown in the drawings, and are only for convenience of description and simplicity of description, but do not indicate or imply that the device or element referred to must have a particular orientation, be constructed and operated in a particular orientation, and therefore, are not to be construed as limiting the present invention. Furthermore, the terms "first", "second", etc. are used for descriptive purposes only and are not to be construed as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Thus, a feature defined as "first," "second," etc. may explicitly or implicitly include one or more of that feature. In the description of the present invention, "a plurality" means two or more unless otherwise specified.

In the description of the present invention, it is to be noted that, unless otherwise explicitly specified or limited, the terms "mounted," "connected," and "connected" are to be construed broadly, and may be, for example, fixedly connected, detachably connected, or integrally connected; can be mechanically or electrically connected; they may be connected directly or indirectly through intervening media, or they may be interconnected between two elements. The specific meaning of the above terms in the present invention can be understood by those of ordinary skill in the art through specific situations.

The present invention will be described in detail below with reference to the accompanying drawings in conjunction with embodiments.

The raw materials used in the embodiments and the comparative examples of the present invention are commercially available products, and the components and the proportions thereof in the silicon-carbon negative electrode material are known to those skilled in the art and can be freely adjusted as needed.

Example 1

(1) Negative electrode

Inner silicon carbon layer 2 formula: 30% of silicon carbon, 66% of graphite, 1% of conductive agent SP, 0.5% of conductive agent CNT and 2.5% of binder PAA. The dispersing agent is deionized water, and the solid content of the cathode slurry obtained by mixing is 50%;

surface silicon carbon layer 3 formula: 90% of graphite, 5% of conductive agent SP and 5% of binder PAA. The dispersing agent is deionized water, and the solid content of the cathode slurry obtained by mixing is 50%;

the preparation process of the cathode comprises the following steps: coating the negative electrode slurry on a copper foil 1 with the thickness of 6um in an extrusion coating mode according to the formula of the inner silicon-carbon layer 2 and the formula of the surface silicon-carbon layer 3 in sequence, wherein the double-sided density of the inner silicon-carbon layer 2 is 15mg/cm ² The surface silicon-carbon layer 3 has a double-sided surface density of 3mg/cm ² . And rolling and cutting the negative electrode after coating.

(2) Positive electrode

The positive electrode formula comprises: 97% of nickel cobalt lithium manganate, 1% of conductive agent SP, 1% of conductive agent CNT and 1% of binder PVDF. The dispersing agent is NMP, and the solid content of the anode slurry obtained by mixing is 75%. The positive electrode slurry was coated on a copper foil 1 having a thickness of 12 um. And rolling and cutting the positive electrode after coating.

(3) The diaphragm is a polyolefin diaphragm.

(4) The electrolyte is carbonate electrolyte, and the concentration of LiPF6 is 1.2M.

(5) Packaging into a PET/aluminum/PP composite aluminum-plastic film.

And assembling the negative electrode, the positive electrode, the diaphragm, the electrolyte and the aluminum-plastic film, and pre-charging and forming to obtain the finished battery.

Example 2

(1) Negative electrode

Inner silicon carbon layer 2 formula: 30% of silicon carbon, 66% of graphite, 1% of a conductive agent SP, 0.5% of a conductive agent CNT and 2.5% of a binder PAN. The dispersing agent is deionized water, and the solid content of the cathode slurry obtained by mixing is 50%;

formulation of surface silicon carbon layer 3: 80% of graphite, 10% of conductive agent SP and 10% of binder PAA. The dispersing agent is deionized water, and the solid content of the cathode slurry obtained by mixing is 50%;

the preparation process of the negative electrode comprises the following steps: coating the negative electrode slurry on a copper foil 1 with the thickness of 6um in an extrusion coating mode according to the formula of the inner silicon-carbon layer 2 and the formula of the surface silicon-carbon layer 3 in sequence, wherein the double-sided density of the inner silicon-carbon layer 2 is 16mg/cm ² The surface silicon-carbon layer 3 has a double-sided surface density of 2mg/cm ² . And rolling and cutting the negative electrode after coating.

The rest is the same as in example 1.

Comparative example

The cathode formula is as follows: 30% of silicon carbon, 66% of graphite, 1% of conductive agent SP, 0.5% of conductive agent CNT and 2.5% of binder PAA. The dispersing agent is deionized water, and the solid content of the cathode slurry obtained by mixing is 50%;

coating the negative electrode slurry on the copper foil 1 with the thickness of 6um by an extrusion coating mode according to a negative electrode formula, wherein the density of the double surfaces of the inner layer is 17.5mg/cm ² The surface layer has a double-sided surface density of 2mg/cm ² . And rolling and cutting the negative electrode after coating.

The rest is the same as in example 1.

Cycle testing

The batteries manufactured in examples 1 to 2 and comparative example were subjected to cycle tests. The environmental temperature is 25 ℃, the cycle voltage interval is 2.75-4.25V, the current is 1C, and the test results are shown in Table 1.

TABLE 1 results of the cycling tests

Scheme(s)	Capacity retention rate	Number of cycles
			Example 1	80％	622
Example 2	80％	678
			Comparative example	80％	425

It can be seen from the results of table 1 that, compared with the comparative example, the batteries obtained in examples 1-2 have more cycle numbers under the same capacity retention rate, because the utility model discloses use the negative electrode material with double-layer silicon carbon layer in examples 1-2, the amount of silicon carbon contained in the surface silicon carbon layer is lower, the binder content is higher, the expansion rate is low, and the amount of silicon carbon contained in the inner silicon carbon layer is higher, the binder content is lower, the expansion rate is high, the surface silicon carbon layer can play a binding role to the expansion of the inner silicon carbon layer, can inhibit the expansion of silicon carbon negative electrode surface, prevent the occurrence of cracking and pulverization, reduce the battery capacity decay rate.

The above description is only a preferred embodiment of the present invention, and should not be taken as limiting the invention, and any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A low expansion silicon carbon anode characterized by: the current collector comprises a current collector and a plurality of silicon carbon layers sequentially coated on the current collector from inside to outside, and the expansion rates of different silicon carbon layers are sequentially reduced from inside to outside.

2. The silicon carbon anode of claim 1, wherein: the current collector is a copper foil, and the thickness of the current collector is 5-10 mu m.

3. The silicon carbon anode of claim 1, wherein: the density of the two surfaces of the silicon-carbon layer of the innermost layer is 15mg/cm ² 。

4. The silicon carbon anode of claim 1, wherein: the double-sided surface density of the silicon-carbon layer of the outermost layer is 3mg/cm ² 。

5. A lithium ion battery using the silicon carbon negative electrode as defined in any one of claims 1 to 4.