TECHNICAL FIELD

The invention relates to a sulfide solid electrolyte.

BACKGROUND ART

With the rapid spread of information-related devices and communication devices such as personal computers, video cameras, mobile phones in recent years, the development of batteries used as power sources thereof has been emphasized. Among the batteries, lithium ion batteries are attracting attention from the viewpoint of high energy density.

A liquid electrolyte comprising a flammable organic solvent is used in conventional lithium-ion batteries currently on the market. Therefore, conventional lithium-ion batteries need attachment of a safety device which suppresses a temperature rise during a short circuit, and improvements in structure and material to prevent a short circuit. On the other hand, it is thought that, since a lithium ion battery obtained by allowing a battery to be totally solid by using a solid electrolyte instead of liquid electrolyte does not use a flammable organic solvent in a battery, simplification of a safety device can be attained, and a production cost can be saved or productivity can be improved.

A sulfide solid electrolyte is known as a solid electrolyte used in a lithium-ion battery. While there are various known crystal structures of sulfide solid electrolytes, a stable crystal structure which is difficult to change in structure in a wide temperature range is suitable from the perspective of widening the use temperature area of a battery. As such sulfide solid electrolytes, for example, sulfide solid electrolytes having argyrodite-type crystal structures (for example, see Patent Documents 1 to 5) have been developed.

RELATED ART DOCUMENTS

Patent Documents

Patent Document 1: JP 2010-540396 A

Patent Document 2: WO 2015/011937

Patent Document 3: WO 2015/012042

Patent Document 4: JP 2016-24874 A

Patent Document 5: WO 2016/104702

SUMMARY OF THE INVENTION

Sulfide solid electrolytes having argyrodite-type crystal structure are highly stable and some have high ionic conductivity. However, further improvements in such as processability at the time of manufacturing a battery and ionic conductivity are required.

It is an object of the invention to provide sulfide solid electrolytes having good processability at the time of manufacturing a battery and high ionic conductivity.

As a result of intensive studies by the present inventors, sulfide solid electrolytes having characteristics differing from those of conventional sulfide solid electrolytes having argyrodite-type crystal structure have been discovered. In the sulfide solid electrolytes according to one embodiment of the present invention, a peak having a half-value width of 500 to 800 Hz are observed in solid-state31P-NMR measurements. Further, in the sulfide solid electrolytes according to the one embodiment of the present invention has a diffraction peak A at 2θ=25.2±0.5 deg, and a diffraction peak B at 29.7±0.5 deg in powder X-ray diffraction, and a Si-relative half-value width of the diffraction peak B is 1.3 or more and 3.0 or less, and a Si-relative peak intensity of the diffraction peak B is 0.01 or more and 0.15 or less. The above features are not observed in conventional sulfide solid electrolytes.

The present invention has found that the novel sulfide solid electrolyte having the above-mentioned characteristics has excellent processability, specifically, compaction property at the time of manufacturing a battery, and high ionic conductivity.

According to one embodiment of the present invention, there is provided a sulfide solid electrolyte comprising lithium, phosphorus and sulfur, having a diffraction peak A at 2θ=25.2±0.5 deg and a diffraction peak B at 29.7±0.5 deg in powder X-ray diffraction using CuKα radiation, and having a peak observed in the range of 60 to 120 ppm in solid state31P-NMR measurements, and having at least one half-value width of the peak obtained by peak-separating the peaks is 500 to 800 Hz.

According to another embodiment, there is provided sulfide solid electrolytes comprising lithium, phosphorus, and sulfur, having a diffraction peak A at 2θ=25.2±0.5 deg, a diffraction peak B at 29.7±0.5 deg, a Si relative half-value width of the diffraction peak B of 1.3 or more and 3.0 or less, and a Si relative peak intensity of the diffraction peak B of 0.01 or more and 0.15 or less in powder X-ray diffraction using CuKα rays.

According to one embodiment of the present invention, it is possible to provide sulfide solid electrolytes having good processability and high ionic conductivity at the time of manufacturing a battery.

