CN106252625B

CN106252625B - Preparation method of graphite negative electrode material of lithium ion battery for EV (electric vehicle)

Info

Publication number: CN106252625B
Application number: CN201610741674.6A
Authority: CN
Inventors: 杨再颖; 谢秋生; 仲林; 陈然; 李长浩; 王旭峰; 娄文君
Original assignee: Ningbo Shanshan New Material Tech Co ltd
Current assignee: Ningbo Shanshan New Material Tech Co ltd
Priority date: 2016-08-26
Filing date: 2016-08-26
Publication date: 2022-06-07
Anticipated expiration: 2036-08-26
Also published as: CN106252625A

Abstract

The invention relates to the technical field of graphite cathode materials, in particular to a preparation method of a graphite cathode material of a lithium ion battery for EV (electric vehicle), which is characterized by comprising the following preparation steps: mixing natural graphite and tar, wherein the weight ratio of the natural graphite to the tar is 60: 40-95: 5; carrying out cold isostatic pressing treatment on the natural graphite mixed with the tar; then carrying out heat treatment at 300-700 ℃ in a hot VC machine; mixing and carbonizing the heat-treated natural graphite mixed with tar and high-temperature asphalt, wherein the temperature of the carbonizing treatment is 1000-1900 ℃, and the time of the carbonizing treatment is 10-50 hours; the EV natural graphite with the surface modified and the compact interior is prepared. Compared with the prior art, the prepared product has high discharge capacity and first discharge efficiency, good cycle performance and excellent comprehensive performance of the prepared half cell.

Description

Preparation method of graphite negative electrode material of lithium ion battery for EV (electric vehicle)

Technical Field

The invention relates to the technical field of graphite cathode materials, in particular to a preparation method of a graphite cathode material of a lithium ion battery for EV.

Background

Compared with the original battery, the lithium ion battery has been rapidly popularized in the aspects of mobile phones, notebook computers, electric tools and the like due to the characteristics of high energy density, long cycle life, no memory effect and the like. In recent years, as a new application of effectively utilizing the characteristics of a lithium ion battery such as small volume and light weight, a battery for an Electric Vehicle (EV) driven by a motor has been actively developed, and it has been a major point of research and development to improve the specific capacity of a negative electrode material of a lithium ion battery, to reduce the first irreversible capacity, and to improve the cycle stability.

The natural graphite used by the lithium ion secondary battery cathode material has an ideal layered structure, has very high discharge capacity (close to theoretical capacity 372mAh/g), is low in cost but has an unstable structure, so that the co-intercalation of solvent molecules is easily caused, and the interlayer falls off in the charge and discharge process, so that the battery has poor cycle performance and poor safety.

Therefore, in order to overcome the performance deficiency of natural graphite, the prior art carries out modification treatment on the natural graphite. In japanese patent JP10294111, the graphite carbon material is coated with pitch at a low temperature, and after coating, non-melting treatment and light pulverization are required, which makes uniform coating difficult. Japanese patent JP11246209 discloses a method of impregnating graphite and hard carbon particles in pitch or tar at a temperature of 10-300 ℃, followed by solvent separation and heat treatment, which is difficult to form a highly polymerized pitch layer having a certain thickness on the surface of the graphite and hard carbon, and is limited in improvement of structural stability of natural graphite. JP2000003708 rounds graphite material mechanically, then impregnates it in heavy oil, tar or pitch, separates and washes it, just like JP11246209 in terms of coating method. Japanese patent JP2000182617 uses natural graphite and the like to carbonize together with asphalt or resin or a mixture thereof, and the method can reduce the specific surface area of the graphite material, but cannot achieve better control on the coating effect. JP2000243398 discloses a method for surface treatment of graphite material by utilizing the atmosphere generated by pyrolysis of pitch, which is unlikely to improve the morphology of the modified material, and thus the improvement of the electrical properties is limited. JP2002042816 uses aromatic hydrocarbon as raw material and coats it with CVD method or pitch phenolic resin, which is similar to JP2000182617 and JP2000283398 in effect.

Disclosure of Invention

The invention aims to overcome the defects of the prior art and provides a preparation method for heating natural graphite mixed tar by a cold isostatic pressing hot VC machine, coating high-temperature asphalt on the surface and carbonizing.

In order to achieve the purpose, the preparation method of the graphite cathode material of the lithium ion battery for the EV is designed, and is characterized by comprising the following preparation steps:

(1) mixing natural graphite and tar, wherein the weight ratio of the natural graphite to the tar is 60: 40-95: 5;

(2) carrying out cold isostatic pressing treatment on the natural graphite mixed with the tar;

(3) then carrying out heat treatment at 300-700 ℃ in a heat VC machine;

(4) mixing and carbonizing the heat-treated natural graphite mixed with tar and high-temperature asphalt, wherein the temperature of the carbonizing treatment is 1000-1900 ℃, and the time of the carbonizing treatment is 10-50 hours; the EV natural graphite with the surface modified and the compact interior is prepared.

The natural graphite is spherical natural graphite.

The tar is coal tar or petroleum heavy oil.

The natural graphite for EV has an average particle size of 5-25 μm and a specific surface area of 4.0m²Less than or equal to g, the first discharge capacity is more than or equal to 365mAh/g, the first charge-discharge efficiency is more than or equal to 95.0 percent, and the discharge capacity retention rate is more than or equal to 85 percent after 300 cycles of charge-discharge cycle

Compared with the prior art, the preparation method can effectively solve the problems of the existing material, and obtains the modified natural graphite cathode material which is subjected to internal densification surface coating and carbonization treatment, wherein the natural graphite surface coating high-temperature asphalt and carbonization process are simple, convenient and easy to implement, the raw material source is wide, and the cost is low; because of adopting the methods of internal densification surface modification treatment, carbonization and the like, the prepared product has high discharge capacity and first discharge efficiency, good cycle performance and excellent comprehensive performance of the prepared half cell.

Drawings

Fig. 1 is a first charge-discharge curve of the graphite negative electrode material of the present invention.

FIG. 2 is a scanning electron microscope image of the graphite cathode material of the present invention.

Fig. 3 is a graph showing cycle performance of the graphite negative electrode material of the present invention.

Detailed Description

The present invention will now be further described with reference to examples.

Examples 1 to 7

The preparation method of the examples 1 to 7 is shown in the following table:

the raw materials in the embodiments 1 to 7 are all conventional commercial products, and the natural graphite is spherical natural graphite.

The following is specifically illustrated by example 2:

mixing 20kg of spherical natural graphite with 2kg of coal tar, placing the mixture into a cold isostatic press for cold isostatic pressing, heating the mixture in a hot VC (vitamin C) machine after discharging the mixture to 600 ℃, mixing high-temperature asphalt according to the weight ratio of 100: 4 after cooling and discharging the mixture, and carrying out carbonization and high-temperature treatment on the natural graphite at 1500 ℃ for 30 hours to obtain the graphite cathode material of the lithium ion battery. The capacity of the half cell is 368.7mAh/g, and the first efficiency is 96.0%.

The method for testing the half cell comprises the following steps: adding conductive carbon black into a carboxymethyl cellulose (CMC) aqueous solution, then adding a graphite sample, finally adding Styrene Butadiene Rubber (SBR), uniformly stirring, and uniformly coating the slurry on a copper foil on a coating machine to prepare a pole piece. And (3) putting the coated pole piece into a vacuum drying oven at the temperature of 110 ℃ for vacuum drying for 4 hours, taking out the pole piece, and rolling the pole piece on a roller press for later use. The simulated cell was assembled in an argon-filled German Braun glove box with an electrolyte of 1M LiPF6+ EC: DEC: DMC 1: 1 (volume ratio) and a metallic lithium plate as the counter electrode. The capacity test was carried out on an ArbinBT2000 model U.S. Battery tester, with a charge-discharge voltage range of 0.005 to 2.0V and a charge-discharge rate of 0.1C.

The full cell testing method used by the invention comprises the following steps: the graphite of the embodiment or the comparative example of the invention is used as a negative electrode, lithium cobaltate is used as a positive electrode, 1M-LiPF6EC, DMC, EMC (volume ratio) is 1: 1 solution is used as electrolyte to assemble a full cell, and the capacity retention rate is more than 85.0% in the test 1C charging and discharging cycle for 300 weeks, as shown in FIG. 3.

The performance parameters of the examples and comparative examples are shown in the following table:

as can be seen from the above data, the discharge capacity and the first efficiency in the comparative example are low, the discharge capacity of the natural graphite which is not treated by tar is the lowest, namely 354.1mAh/g, the first efficiency is only 90.2%, and the capacity retention rate reaches only 70% after 300 cycles. The capacity of the negative electrode material prepared by the method is more than 365mAh/g, the efficiency is more than 95.0%, and the capacity retention rate is more than 85% after 300 cycles, which is shown in figures 1 to 3.

Claims

1. A preparation method of a graphite cathode material of a lithium ion battery for EV is characterized by comprising the following preparation steps:

(3) then carrying out heat treatment at 300-700 ℃ in a heat VC machine;

2. The method for preparing the graphite anode material for the EV lithium ion battery as claimed in claim 1, wherein the natural graphite is spherical natural graphite.

3. The method for preparing the graphite negative electrode material for the lithium ion battery of the EV according to claim 1, wherein the tar is coal tar or petroleum heavy oil.

4. The preparation method of the graphite anode material for the lithium ion battery for the EV according to claim 1, wherein the natural graphite for the EV has an average particle size of 5-25 μm and a specific surface area of 4.0m²The discharge capacity is less than or equal to g, the first discharge capacity is more than or equal to 365mAh/g, the first charge-discharge efficiency is more than or equal to 95.0 percent, and the discharge capacity retention rate is more than or equal to 85 percent after 300 cycles of charge-discharge cycle.