Catalysts and batteries Development of All-Solid-State Ceramic Batteries with Solid Electrolytes Toward the Realization of Next-Generation Batteries Superior to Existing Li-ion Batteries

Electrolytes hold the key to the development of next-generation batteries

The development of next-generation batteries with better performance than current lithium-ion batteries from the perspectives of capacity, cost, and safety will be crucial for electric vehicles, plug-in hybrids, and smart grids (next-generation transmission and distribution networks) to permeate society. The key to this development lies in a single constituent material of batteries called “electrolytes.”

While today’s Li-ion batteries employ organic liquid electrolytes, we are using solid electrolytes in an effort to develop all-solid-state batteries whose materials, including the cathode and anode, are wholly solid. The use of solid electrolytes can lead to concepts that upend existing conventions for battery pack design, such as bipolar laminated structures that cannot be formed in conventional electrolyte systems, and is expected to produce batteries with higher capacity and higher power. Moreover, electrolytes in a solid state improve battery safety.

All-solid-state batteries possessing more than 3 times the power of conventional Li-ion batteries

We discovered Li₁₀GeP₂S₁₂, a material possessing ionic conductivity that rivals organic electrolytes. Thereafter, we also found Li_9.54Si_1.74P_1.44S_11.7Cl_0.3 possessing the highest ionic conductivity, Li_9.6P₃S₁₂² that has a large electrochemical window and can be used as electrolyte for lithium-metal anodes, and the SnSi-based material Li_10+δ[Sn_ySi_1-y]_1+δP_2-δS₁₂ that is less expensive and easy to synthesize.

Using these electrolytes, we manufactured all-solid-state ceramic batteries that are much-anticipated for their noncombustibility and safety aspects, and demonstrated their inherent potential for much faster charging and higher power than today’s Li-ion batteries. These all-solid-state batteries showed more than three times the power at room temperature than conventional Li-ion batteries and excellent charging/discharging properties at both low temperatures (-30℃) and high temperatures (100℃), which is a shortcoming of Li-ion batteries employing organic electrolytes.

Crystal structure analysis through neutron diffraction revealed that Li_9.54Si_1.74P_1.44S_11.7Cl_0.3 possesses a three-dimensional framework structure (Figure 1) in which lithium forms a series of chain-like units and three-dimensional conduction pathways at room temperature, yielding high lithium-ion conductivity.

The all-solid state batteries developed in this study clearly possess power and energy characteristics that far exceed those of not only existing Li-ion batteries, but also the various batteries currently being developed as next-generation batteries (Figure 2).

Figure 1 3D framework structure of Li_9.54Si_1.74P_1.44S_11.7Cl_0.3 and the distribution of Li at room temperature

Figure 2 Comparing specific power and energy for various electrochemical devices; all-solid state batteries combine the features of storage batteries with capacitors