Method for uniformly and controllably coating conducting carbon layer at surface of LiFePO4 granule surface

[0025] Example 1.

[0026] Put LiFePO 4 The powder is placed in the constant temperature zone of the chemical vapor deposition furnace, and then evacuated for 1 hour (the vacuum degree reaches about 10Pa). After the air in the furnace is exhausted, nitrogen is introduced. After the temperature is increased to 720°C, acetylene gas is introduced for chemical vaporization. Deposition. In the furnace gas, the volume percentage of acetylene gas is 20%, and the deposition time is 2 hours. The deposited carbon sample is cooled to room temperature with the furnace and taken out. X-ray diffraction analysis was performed on the sample of deposited carbon, and the sample before deposition ( Figure 1a )Compare found LiFePO 4 The structure of has not changed after carbon deposition ( Figure 1b ). Transmission electron microscopy observation results show that the thickness of the deposited carbon layer is very uniform ( Figure 2a ), the thickness of the carbon layer is about 20 nanometers ( Figure 2b ). The apparent conductivity of the deposited carbon sample is 1.72Ω -1 ·M -1 , And the sample before carbon deposition (apparent conductivity 9.23×10 -6 Ω -1 ·M -1 Compared with ), the conductivity is improved by five orders of magnitude. Apparatus for measuring apparent conductivity see image 3. Apparent electrical conductivity measurement method: powder sample 2 is molded in a plexiglass mold 1 under a pressure of 50 MPa to achieve a density of about 22%, and then the stainless steel upper indenter 3, lower indenter 4 and the electrodes of the chemical workstation are connected for measurement resistance. The voltage scan interval is -0.5V to +0.5V, the scan rate is 1V/s, and the voltage-current curve is recorded. The slope of the curve is the resistance. The resistivity is obtained from the resistance according to the sample size, and the reciprocal of the resistivity is the conductivity. Electrical conductivity usually refers to dense samples. Because it is a powder sample, the measured resistance has a great relationship with the density of the powder sample after molding, so it is defined here as the apparent conductivity (conductivity under the measurement conditions).

[0027] Example 2.

[0028] The difference from Example 1 lies in:

[0029] Put LiFePO 4 The powder is placed in the constant temperature zone of the chemical vapor deposition furnace, and then evacuated for 1 hour (the vacuum degree reaches about 10Pa). After the air in the furnace is exhausted, nitrogen is introduced. After the temperature is raised to 700°C, acetylene gas is introduced for chemical vaporization. Deposition. In the furnace gas, the volume percentage of acetylene gas is 5%, and the deposition time is 2 hours. Transmission electron microscope observation results show that the thickness of the deposited carbon layer is about 5 nanometers, and the thickness is very uniform ( Figure 4 ). The apparent conductivity of the deposited carbon sample is 1.04Ω -1 ·M -1.

[0030] Example 3.

[0031] The difference from Example 1 lies in:

[0032] Put LiFePO 4 The powder is placed in the constant temperature zone of the chemical vapor deposition furnace, and then purged with argon for 2 hours. After the temperature is raised to 700°C, acetylene gas is introduced for chemical vapor deposition. In the furnace gas, the volume percentage of acetylene gas is 20%, and the deposition time is 0.5 hours. Transmission electron microscope observation results show that the thickness of the deposited carbon layer is about 8 nanometers, and the thickness is very uniform ( Figure 5 ). The apparent conductivity of the deposited carbon sample is 1.29×10 -1 Ω -1 ·M -1.