## Tokyo Tech team develops low-cost germanium-free solid electrolyte for Li-ion batteries

##### 14 July 2017

Researchers at Tokyo Institute of Technology have devised a low-cost, scalable approach to developing all-solid-state batteries, improving prospects for scaling up the technology for widespread use in electric vehicles, communications and other industrial applications.

Described in a paper in the ACS journal Chemistry of Materials, the approach involves substituting germanium in the solid electrolyte for two more readily available elements: tin and silicon. The new material achieved an ionic conductivity that exceeds that of liquid electrolytes. Reporting the findings, Ryoji Kanno and colleagues stated: “This germanium-free lithium conductor could be a promising candidate as an electrolyte in all-solid-state batteries.

All-solid-state systems with solid electrolytes (SEs) are potential candidates for next-generation batteries and are expected to provide a high power and energy density with reliable and improved safety characteristics. Sulfide-based lithium-ion conductors have the advantages of high conductivities together with suitable electrochemical windows and mechanical properties; thus, they are intensively studied as promising SEs. Li10GeP2S12 (LGPS) is a new member in the crystalline sulfide electrolyte family and exhibits an ionic conductivity of 1.2 × 10−2 S cm−1, which is comparable to that of organic liquid electrolytes. The all-solid-state battery, LiCoO2/LGPS/In−Li, showed excellent charge−discharge characteristics using the LGPS electrolyte. However, Ge is a relatively expensive element and could limit the widespread use of LGPS materials.

The type of crystal structure is an important component in the design of ionic conductors. Materials with similar types of structures and high ionic conducting solids might provide high conducting characteristics. The LGPS-type structure is suitable for high ionic diffusion along the one-dimensional tunnels and/ or two-dimensional planes that participate in high ionic diffusion. Si- and Sn-based analogous with Ge-free materials might be promising as SEs for practical applications.

—Sun et al.

 The atomic arrangement of the new material named LSSPS. Two representations of the new germanium-free material with the structure Li10.35[Sn0.27Si1.08]P1.65S12 (Li3.45[Sn0.09Si0.36]P0.55S4.

Compared to conventional lithium-ion batteries that contain lithium ion conducting liquids, all-solid-state batteries of the future promise a suite of advantages: improved safety and reliability, higher energy storage and longer life cycles.

The discovery of superionic conductors—solid crystals that enable fast movement of ions—is spurring the development of such batteries, but promising designs have so far relied on the use of rare metals such as germanium, making them too expensive for large-scale applications.

Due to its high chemical stability and ease of fabrication, Kanno says that the new material widens the possibilities of fine-tuning solid electrolytes to meet diverse industry and consumer needs.

In 2011, Kanno and his team, working in collaboration with Toyota Motor Corporation and Japan's High Energy Accelerator Research Organization (KEK), published a landmark paper in Nature Materials that introduced a solid electrolyte with the structure Li10GeP2S12 (LGPS). This material became an important forerunner in the race to develop viable all-solid-state batteries. It exhibited an ionic conductivity of 1.2 x 10-2 S cm-1 at room temperature, a level comparable with—and even exceeding some—liquid electrolytes used in existing batteries.

The team went on to design other solid electrolytes based on the same LGPS crystal structure, with promising results.

In their latest study, the researchers kept the same framework structure of LGPS, and finely adjusted the ratio and positioning of the tin, silicon and other constituent atoms. The resulting material LSSPS (composition: Li10.35[Sn0.27Si1.08]P1.65S12 (Li3.45[Sn0.09Si0.36]P0.55S4)) achieved an ionic conductivity of 1.1 x 10-2 S cm-1 at room temperature, almost reaching that of the original LGPS structure.

Although further work will be required to optimize performance for different usage purposes, the new material raises hopes for low-cost production without sacrificing performance.

 Cyclic voltammogram and charge-discharge curves. The material exhibits high stability and cycling ability, with good capacity retention during 20 cycles. Click to enlarge.

Resources

• Yulong Sun, Kota Suzuki, Satoshi Hori, Masaaki Hirayama, and Ryoji Kanno (2017) “Superionic Conductors: Li10+δ[SnySi1–y]1+δP2−δS12 with a Li10GeP2S12-type Structure in the Li3PS4–Li4SnS4–Li4SiS4 Quasi-ternary System” Chem. Mater. doi: 10.1021/acs.chemmater.7b00886

This could become the battery that Toyota has been working on and waiting for to switch to lower cost improved BEVs.

Could this improved lower cost solid state battery be mass produced by 2020 or shortly thereafter?

Will variations of the technology do even better a few years latter?

Superionic Solid Electrolytes will definitely be a component of the next gen battery. Work by John Goodenough, M. Helena Braga, and Andrew J. Murchison from UT Austin, also PATHION Inc. as well as other researchers are looking into these electrolytes.

Harvey,

Audi already has batteries at $114/kWh now. What goal do they have to hit by 2020 to be "low cost and mass produced"? And where is gorr today? I miss my daily dose of drug induced conspiracy/hysteria. LOL Just blah blah without a prototype battery running in a real battery car with a measurable range and estimated longevity. With that we will definatly have to wait 15 to 20 years to beat a small gasoline on cost per mile driven. These reports are just released to justify the subsidies they receive and they probable covertly sell the patents to shell or exxon mobil in Guyana. Ohh, wait, If they had tested this battery in a known bev like the leaf or bolt or tesla model 3 or s or x and they would have had a range of 600 miles for the same price and easy repeatable fast charging, they would have stop these bev sales and everybody would have decided to wait instead of buying these actual bevs. I knew gorr couldn't stay away for long. Funny how Gorr knows the secrets of the world even as the oil companies and OPEC are quintupling their estimates of EVs and admitting that they will displace 8 million barrels of oil a day. But you go with it gorr...we can all use the laugh. Just had to toll that bell, didn't ya Dave...$100/kWh batteries don't just put EVs on cost parity with ICEs, they also reposition renewables (with sufficient production capacity).

$100/kWh is about what pumped hydro costs. A 30kW battery would be enough for most homes in mild climates to run overnight on self generated energy. Second life batteries from EVs could easily serve this application, probably at a lower price point. It seems this will ultimately put a ceiling on electric rates, which will track the cost of solar production. Yes e.c.i.c, lower cost, higher efficiency solar panels and/or larger wind turbines installed on higher towers + lower cost batteries (below$100/KWh) will knock NPPs, CPPs and NGPPs out of business within 10 years or so.

The gradual switch over could start as early as 2020.

About 250,000 coal miners and CPP/NPP specialists will have to be recycled/retrained to seek and destroy fake news broadcasters and IS members?

That's a pretty dark view, Harvey.

Imagine instead they were retrained to install the solar, wind and stationary storage systems which will replace their obsolete mines, transport systems and power plants.

No doubt some could be employed in remediating the landscape they drilled and scraped so effectively. Plant beetle-resistant lodge pole pines perhaps.

ECI,
Huge Grin...Yep LOL It's just so tiring to hear the conspiracy theories and gorr has started going on to every blog/forum he can find to start that crap. It's like dealing with the Trump supporters now: facts and reality have nothing to do with it anymore. They've turned themselves into some type of martyred fossil-fuel cult.

Harvey,

I'm sorry that people have to change because it's never easy. But we can't bring back coal jobs anymore than we can bring stable hand jobs back to every corner of America. We just don't use horses for transportation.

But there are literally millions of jobs that will be created as we build out the renewables and the grid has to be upgraded and updated whether we go to renewables or not. Right now it's totally vulnerable to cyber attacks from those Russian idiots as they prepare for the next stage of cyber war.

So there are plenty of jobs that will be created no matter where the energy comes from. People are going to have to be retrained and there is nothing we can do to turn back the clock on that.

I can not see someone wanting black lung disease versus putting up solar panels and wind turbines. There are less than 100,000 coal jobs.

The 37.8 million dollars in grants for the AC project and Sunline project will cover a grand total of 25 fuel cell busses. Those 25 will nearly double the total fuel cell busses in the US.

Meanwhile there were 94K battery electric busses sold world wide last year. Not only are electrics cheaper to operate and maintain they are now cheaper to purchase than diesel, gas, and CNG busses. Contrast that with the million dollars plus per FC bus.

FCs are making progress but they have a long way to go before they are financially viable. Their problem is that battery electrics are years ahead and also advancing.

Extended range electric buses initial purchase price is still much higher than diesel equivalent. Lifetime cost may be very different and may soon favour e-buses.

FC buses (especially those built in Asia/China) will soon compete with both and could even last longer

With mass produced, longer life, solid states batteries (lower cost - below \$100/kWh), the initial cost of extended range e-buses will probably match equivalent diesel units.

Extended range FC hybrid buses will compete and have the advantage of being able to operate on both electricity and H2 depending on batteries and FCs installed?

Diesel buses will be progressively phased out of service in the next 15 years or so.

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