## New thermally durable solid-state Li-ion battery technology from Hitachi and Tohoku University

##### 07 December 2015

Hitachi, Ltd. and Tohoku University’s Advanced Institute for Material Research (AIMR) have demonstrated technology reducing the internal resistance of all-solid-state lithium ion batteries (Li-ion battery) through the use of LiBH4-based complex hydrides as novel solid electrolytes.

The reduction of internal resistance improves the charge-discharge performance of the all-solid-state Li-ion battery, resulting in the batteries (capacity: 2 mAh, density: 30 Wh/L) successfully operating at temperatures as high as 150 ˚C with a discharge capacity of 90% of theoretical value.

This technology is significant as it allows the thermally durable Li-ion battery to be used in a wider variety of applications. Because this technology does not require the cooling system common in conventional Li-ion batteries, Hitachi expects it to lead to the development of more compact battery systems and to reduce overall costs.

This research was part of a collaborative project between Hitachi and AIMR has developed the new technology to reduce the internal resistance that is a factor of deterioration of charge-discharge performance.

A conventional Li-ion battery consists of a separator, a positive electrode (cathode), and a negative electrode (anode). The battery is filled with organic electrolyte solution in which lithium ions move between the two electrode layers during the charge and discharge process. One issue with conventional Li-ion batteries is the thermal durability of the organic electrolyte solution.

The upper operating temperature is limited to around 60 ˚C owing to the volatility of the organic electrolyte. Consequently, it is difficult to use the conventional Li-ion battery in a high temperature environment without a cooling system.

While solid electrolytes with no volatility have been developed for use in a high temperature environment, the lithium ion conductivity of the solid electrolyte, is lower than that of the organic electrolyte solution. The internal resistance of all-solid-state Li-ion battery needs to be reduced for its commercialization.

 Schematic illustration of conventional Li-ion battery (left) and new solid-state battery (right). Source: Hitachi. Click to enlarge.

Details of the new battery technology include:

1. Composite positive electrode layer to suppress the decomposition of active materials at interface. One potential issue is that Li-ion conductivity will be inhibited by the decomposition of the cathode material, which is reduced by LiBH4-based complex hydrides. To solve this issue, a Li-B-Ti-O-based oxide material was developed to form a dense composite positive electrode with the active materials. The Li-B-Ti-O in the electrode effectively protected the active materials, and suppressed the increment of internal resistance caused by the decomposition. In consequence, the discharge capacity of the battery was improved from 0 to 50% of theoretical value.

2. Adhesive layer for reducing the interface resistance between solid electrolyte and composite positive electrode layer.Another issue is that the composite cathode material and the metal hydride complex solid electrolyte layer were delaminated due to the volume change of the active materials during charge-discharge reaction. This causes incremental interfacial resistance by poor lithium ion conduction at the delaminated interface. To prevent delamination of the interface, the team developed an amide-added metal hydride complex with a low melting point for use as an adhesive layer.

As a result, the internal resistance of the all-solid-state Li-ion battery was successfully reduced to 1/100 of the value compared to that of a battery with no adhesive layer.

The discharge capacity was improved up to 90% at 150 ˚C by applying the two technologies. In addition, the degradation of the discharge capacity during charge-discharge cycles was effectively suppressed and the stable charge-discharge of the all-solid-state Li-ion battery was confirmed.

The researchers said that now that they have verified the fundamental operation of a thermally durable all-solid-state Li-ion battery, they intend to look into further improving battery capacity, energy density and charge-discharge duration.

This research was part of a project between Hitachi and AIMR called “Collaborative Research for Next Generation Innovative Battery”. The findings of this research were partially presented on 13 November at The 56th Battery Symposium in Japan.

This is great news.  A battery which can endure a desert hot-soak and needs only a bit of air cooling is going to be much easier and cheaper to package.  I hope by the time my car needs a new battery, something like this is available.

Yes, this could be very good news for HEVs, PHEVs, BEVs and FCEVs if energy density can be multiplied by 3X to 5X (+) at an affordable mass produced price.

If you can get 80% charge in 15 minutes, even a 200-mile battery would be enough for almost everyone.

What many posters like to forget is that a good weather 200 miles maximum can quickly become less than 100 miles on a cold snowy slow traffic day.

Looking for a quick charge station every 100 miles would be a real pain?

So that makes perhaps 10 million out of 20 million Canadians, and maybe 20 million out of 320 million Americans.  That bunch would need a PHEV for the auxiliary heat the engine would provide; the other 90+% would not.

Harvey, just get a PHEV if it scares you that much and give it a rest.

My favorite signature line, seen on a Canadian's email:

"I'm all for global warming!"

I, as many other city dwellers, do not have access to home charging facilities. A PHEV with very limited e-range is not the proper current answer. That's why we temporary use 3 excellent Toyota HEVs.

Since it is almost impossible to convince the majority (currently with large ICEVs) to invest a few thousand $per internal garage unit for proper legal electrical modifications, the situation may not change for another 5 to 10 years or so. By that time, many HEVs and PHEVs may be replaced by affordable extended range BEVs and/or FCEVs. I'm not against PHEVs but the current constrains do not make it a good choice. You mean your current constraints do not make it a good choice for you. A few people who want EVs or PHEVs, or people who realize that EV charging would increase the value of their condo, could change all of that. You are absolutely correct E-P. I'll keep trying a few times a year. I do not know which will come first: 1) extended range affordable BEVs + a network of public quick (10 minutes or so) charge stations or/ 2) a majority accepting to invest a few$K to modify our internal garages electrical distribution system.

Both may take up to 10 years. Our new HEVs will last that long and more.

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