Performance Improvement of Lifepo4 Solar Storage by New Conductive Carbon Material

Lithium-ion batteries are widely used in mobile electronic devices and power tools and other fields, in recent years, with the rapid development of electric vehicle industry, power battery market demand is also expanding rapidly. Electric cars, electric buses in order to ensure the safety of passengers and property, so the safety of battery power requirements are high, especially in the event of a collision and other serious problems, so the battery evaluation indicators for extrusion, acupuncture, etc. Safety indicators have a very stringent requirements. Currently in all the battery materials, lithium iron phosphate material with excellent safety performance has become the preferred material for power battery.

However, lithium iron phosphate materials are also low voltage, poor conductivity and other shortcomings, leading to lithium iron phosphate in the discharge process of polarization, resulting in lower discharge voltage and other issues. In order to improve the conductivity of LiFePO4 LiFePO4 from two aspects of the modified treatment.

One of them is the nano-material processing, the lithium iron phosphate nanoparticles, on the one hand to improve the specific surface area of ​​the material, increasing the contact area and improve the conductivity, but also reduces the Li + diffusion path, High rate of performance of the material. Another method is the surface coating treatment, the current method is more mature lithium iron phosphate particles coated with a layer of graphite layer, thereby enhancing the conductivity of the material.

Wenju Ren, from the Graduate School of Peking University in Shenzhen, studied the structure of the electrode and proposed the concept of the soft carbon conductive agent SCC. The soft carbon material conductive agent produced between the hard carbon conductive agent and the active material particles So that the current distribution and Li + distribution more uniform, thereby reducing the charge and discharge process of the cathode material polarization, which significantly enhance the capacity of the material and rate performance.

Three kinds of conductive carbon materials - spherical, tubular and porous conductive carbon materials with different morphologies were studied. The sp2 / sp3 bonding ratio, crystal structure, surface defects, morphology, specific surface area and Pore ​​structure, and the contact of these carbon materials with LFP particles.

The carbon material of the porous structure has a hair-like morphology and exhibits a very soft state, which can generate a large contact area between the LFP particles, mainly because the carbon material contains a large amount of sp2 (About 80%), a large number of surface defects, a smaller crystal size (about 4 nm), and a large specific surface area (> 1000 m2 / g), so this material is also known as soft carbon material (SCC) While other types of carbon are classified as hard carbon materials (HCC) and carbon nanotubes (CNTs).

The soft carbon material has a large surface defect and a large specific surface area, thus greatly increasing the contact area between the LFP particles, significantly reducing the contact resistance, increase the conductivity of the electrode.

Electrochemical tests show that the plate with SCC conductive agent has a longer discharge voltage platform and a smaller gap between the charge voltage platform and the discharge voltage platform compared with the electrode piece using HCC and CNT conductive agent.

In this study, Wenju Ren conducted a study of several typical conductive carbon materials and found that the soft carbon material due to the larger contact area between the active material makes the current distribution in the charge and discharge process more uniform, thereby reducing the Charge and discharge in the process of LFP electrode polarization phenomenon, improve the LFP material capacity and rate performance. And the soft carbon material SCC is defined for the first time - porous, soft carbon material with hair-like morphology, which can produce large contact area with LFP material; hard carbon material HCC - with spherical structure, and There is a point contact between the active substances.