Lithium Titanate: A Promising Anode Material for Li-ion Power Batteries   

Replacing fuel-powered vehicles with electric vehicles is the best way to solve urban environmental pollution. High-safety Li-ion power batteries have become the ideal source of power for electric vehicles. At the same time, a variety of anode and cathode materials for Li-ion power batteries are also being extensively studied worldwide. Popular cathode materials are lithium cobalt oxide, lithium manganese oxide and lithium iron phosphate. Although graphite is still the most popular anode material, other kinds of anode materials are being developed rapidly, such as tin-based materials, silicon-based materials, metal oxide materials, nitrides and lithium titanate ( Li4Ti5O12, LTO).

   There is a very high requirement for the safety performance of Li-ion power batteries for electric vehicles. But Li-ion power batteries with graphite as the anode electrode have serious safety risks. Because the potential of graphite and metallic lithium's potential are very close, when the battery is overcharged, lithium dendrites can easily form on the surface of the graphite electrode, causing a short circuit, and affecting the safety performance of the Li-ion battery. But Li-ion power batteries with LTO as the anode electrode present high safety performances. Thus, LTO has become one of the best anode materials for Li-ion power batteries.

Features of LTO as an anode material

LTO has a spinel structure. In the 1970s, it was once extensively studied as a superconducting material. In the late 1980s, it was carefully studied as a cathode material for Li-ion batteries. But because its potential vs. Li is low and its energy density is also relatively low, it did not cause much attention at the aspect.
   Not until around 1999 did scientists start to conduct extensive studies on LTO as a Li-ion battery anode material. Lithium ion batteries using LTO as the anode material have a long cycle life, high stability, high safety and small volume changes caused by charges and discharges; and their first charge-discharge efficiency can reach about 95%. In addition, LTO is a zero-strain material. Its actual specific discharge capacity is 165 mAh /g; and its Li-ion diffusion coefficient reaches 2 × 10-8 cm2/s at room temperature, an order of magnitude higher than that of graphite. Higher Li-ion diffusion coefficient can make the anode material charge and discharge more quickly. It does not react with the electrolyte solution and does not easily produce lithium dendrites on its surface. It is also cheap and easy to manufacture. Due to these merits, LTO as an anode material for Li-ion power batteries has bright prospects for commercial applications.
   With LTO is as the anode material and lithium manganese oxide (LMO), lithium nickel-cobalt-manganese oxides or lithium iron phosphate (LFP) as the cathode material, a high-performance Li-ion power battery can be formed. Of course, the anode and cathode electrodes are separated with a separator, and the electrolyte solution is filled between them. After extensive studies, scientists find that LMO and LTO are an ideal mix for Li-ion power batteries. Such a mix has nearly perfect safety performance, long cycle life, fast charge and discharge speeds and low costs. Therefore, industry insiders believe that the LTO+LMO system will be the main anode and cathode materials mix of Li-ion power batteries in the future.

Market prospects of LTO as Li-ion power battery anode material

For power batteries for electric vehicles, it is required that the cycle life of a single cell is greater than 2 000 times and the cycle life of the whole battery is more than 1 200 times. Currently, the cycle life of single cells with LMO as the cathode material and graphite as the anode material can only reach 1 000 times. However, the cycle life of single cells with LMO as the cathode material and LTO as the anode material can reach more than 5 000 times. Even after such cells are repeatedly charged and discharged for 3 000 times, their discharge capacity only decreases by 10%.
   In Japan, studies on LTO as Li-ion power battery anode material are in full swing. Electric scooter EV-neo launched by Honda in December 2010 used Toshiba's Li-ion power bacterial that uses LTO as the anode material. The electric scooter can run 30 km/h and 30 km per charge of electricity.
   LTO has superior safety and cycle life performances, but its specific discharge capacity is relatively low. Scientists at Murata and Toyota also try studying how to combine LTO and silicon to improve the specific discharge capacity of LTO.
   The LTO-based Li-ion battery developed by U.S. battery maker Altair Nanotechnologies (ALTI) may be widely used in electric vehicles (EV) in the future, because it can be charged very fast, in a few minutes instead of a few hours. In addition, it can be recharged for more than 5 000 times. Even if it is charged once a day, it can be used for more than 13 years. It was reported that the ALTI battery has been used on a UK-based EV maker's super sports EVs. And it will soon be used on a USA-based company's EVs. ALTI claims that the battery can be used in environments with temperature ranging from -40 to 55 degrees Celsius.
   In China, CITIC Guoan MGL Power Science & Technology Co Ltd and other companies are also developing Li-ion power batteries which use LMO as the cathode material and LTO as the anode material and will launch some trial products. Zhuhai Yintong New Energy Co Ltd (Yintong) already mass produced LTO-based batteries in the end of 2009. In November 2010, the company invested RMB325 million to acquire 51% of ALTI's shares. With the ALTI technology, Yintong will invest RMB5 billion to build an industrial park, which will cover an area of 260 000 square meters and include a LTO-based Li-ion power battery production base, a new energy technology research institute, a new energy bus assembly line, a new energy vehicle factory, a storage battery plant and an electric unmanned helicopter factory, with a design capacity of 1 billion Ah batteries, 50 000 new energy buses, 50 000 electric taxis, 100 000 official electric cars and 300 000 family electric cars a year. The phase I of the project, with an investment of RMB900 million, was formally put into operation on August 10, 2010, having a production capacity of 100 million Ah batteries a year.
   Due to its high safety, high reliability, long cycle life and environmental friendliness, in next 2 to 3 years LTO will become the anode material of new-generation Li-ion power batteries and be widely used in new energy vehicles, electric motorcycles and other application areas. The market prospect of LTO as Li-ion power battery anode material is bright.