In the early 1970s, the research work of lithium-ion batteries was promoted due to the energy crisis, and lithium primary batteries with Li or Li-Al alloy as negative electrode materials, including Li/MnO2, Li/I2, Li/SOCl2, Li/FeS2, etc., appeared one after another. In 1970, Japan’s panasonic company obtained a patent for Li/(CF)n batteries in the United States, and during the discharge process (CF)n was lithiated into C and LiF, and the reaction was not reversible, so the lithium primary battery at that time was a disposable battery.
After the 1980s, research on lithium-ion batteries made breakthroughs: in 1980, Goodenough’s group made LiCoO2 cathode material; In 1981, Bell Laboratories used graphite in the negative electrode material of lithium-ion batteries because the potential difference between lithium metal and graphitized carbon material and lithium is less than 0. 3V, so the rechargeable lithium-ion battery anode material can be used without lithium metal. In the process of recharging the lithium-ion battery, the lithium first enters the graphite.
Graphene is the basic unit of carbonaceous materials. The ideal graphene lamellar mechanism has an ultra-high specific surface area of 2630.0m2/g and a lithium-ion storage capacity of 744mAh/g. At the same time, the good mechanical properties, optical properties, electrical conductivity and thermal properties of graphene materials also make it an important material for lithium-ion batteries. Lithium vanadium phosphate is a composite of graphene and other materials, and its electrical conductivity is much higher than that of graphene materials.
Lithium-ion batteries are currently the highest energy density of commercial secondary batteries. The most used cathode material for commercial lithium-ion batteries is lithium cobaltate (LiCoO2), but lithium cobaltate is expensive because of cobalt and poor safety, so researchers in various countries have not stopped researching and developing new cathode materials for a moment. Polyanionic compounds are the most promising cathode materials for a new generation of lithium-ion batteries because of their good safety and good impingement/delithium properties.
Due to the addition of carbon in the lithium vanadium phosphate complex, the overall energy density and safety are high, which can not only eliminate the shortcomings of lithium cobalt acid and lithium iron phosphate, but also improve the electrical conductivity . However, vanadium material has the disadvantages of difficult extraction of precursor, high energy loss and high toxicity, so it is very important to analyze the application of graphene in the preparation of lithium vanadium phosphate for lithium ion batteries.
Compared with the traditional battery, the lithium-ion battery with lithium vanadium phosphate as the negative electrode material has the characteristics of large capacity, good safety, long service life and good low temperature performance. At present, the most used cathode materials on the market are lithium cobalt acid, lithium manganese acid, ternary materials and lithium iron phosphate. These batteries have their own characteristics, but one of the disadvantages is that the safety risks are large, the electric vehicle battery explosion or combustion phenomenon, and lithium-ion batteries in the field of electric vehicles to be widely used, safety is the primary problem that must be solved.
The vanadium phosphate lithium-ion battery also has a prominent feature, that is, the low temperature function is very good. At present, the serious aging of batteries at low temperatures is a major problem encountered by new energy vehicles, especially pure electric vehicles. A typical example is the number of pure electric vehicles, which have a driving range of about 200 kilometers, but in the cold winter in the north, the actual driving range after a full charge may only be more than 100 kilometers, and the aging of the battery is also serious.