Toshiba researchers use TiNb2O7 anodes for high-energy, fast-charging, long-life Li-ion batteries for EVs
A team at Toshiba’s Corporate Research & Development Center in Kawasaki, Japan, has developed a high-density TiNb2O7 (HD-TNO) composite electrode consisting of micro-size spherical TNO secondary particles coated with carbon. As reported in a paper in the Journal of Power Sources, the anodes exhibited high-rate capability, long cycle-life, and a high volumetric capacity of more than twice that of LTO composite anodes.
The team fabricated large-size lithium-ion batteries using the HD-TNO anode and a LiNi0.6Co0.2Mn0.2O2 (NCM) cathode with a capacity of 49 Ah for automotive applications. These cells had a high energy density of 350 Wh L-1, a high input-power density of 10 kW L−1 for 10 s at 50% state of charge (SOC), and fast-charging from 0% to 90% SOC in less than 6 min.
By comparison, a comparable LTO/NCM cell showed an energy density of 177 Wh L-1.
High rate discharge tests indicated high capacity retention of 93% at 10 C rate. The capacity retention at 7,000 cycles was 86% by full charge-discharge cycling at 1C rate. Cycle life was predicted to be 14,000 cycles at 80% capacity retention.
Development of large-size lithium-ion batteries for automotive applications such as electric vehicles (EVs) and plug-in hybrid electric vehicles (PHEVs) has focused on enhancement of energy density. However, conventional lithium-ion batteries using graphite anodes have limitations in terms of fast-charging, life, safety, and low-temperature performance, which are important subjects for these applications. In particular, fast-charging performance of a few minutes is a strong requirement for enhancing the convenience and promoting the spread of EVs. Long-life of batteries is also required for reduction of the total cost for long-term using EVs and saving the resource. In terms of safety and life, it is necessary that lithium-ion batteries do not suffer any lithium metal plating on anodes during fast-charging and low-temperature charging even at the end of life.
It is well known that Li4Ti5O12 (LTO) anodes do not undergo lithium metal plating during fast-charging and long-term cycling, which leads to long-life and safety. However, LTO anode-based batteries have the disadvantage of low energy density, which is not suitable for automotive applications such as EVs with long driving ranges. Therefore, our group and Goodenough’s group have recently proposed TiNb2O7 (TNO) with a monoclinic structure as an alternative high-capacity anode material to LTO.
… However, TNO has poor ionic and electronic conductivity in practice. It is necessary to develop TNO composite anodes with good electron-conductive networks and shorter lithium diffusion length in TNO particles in order to enhance the capacity and rate capability for lithium-ion batteries.—Takami et al.
The researchers used micro-size spherical TNO secondary particles coated with carbon to produce high-density electrodes. The micro-size spherical particles have a high tap density and allow reduction of the amounts of carbon conductor and binder additives.
The lithium-ion batteries using the HD-TNO anodes had excellent performance of high energy, fast-charging, and long life for EVs with long driving ranges by fast charging, which is expected to make important contributions to enhancing the convenience and promoting the spread of EV applications such as electric bus, taxi, and autonomous cars.—Takami et al.
Norio Takami, Kazuki Ise, Yasuhiro Harada, Takuya Iwasaki, Takashi Kishi, Keigo Hoshina (2018) “High-energy, fast-charging, long-life lithium-ion batteries using TiNb2O7 anodes for automotive applications,” Journal of Power Sources, Volume 396, Pages 429-436 doi: 10.1016/j.jpowsour.2018.06.059