Published on May 7th, 2015 | by James Ayre6
High Performance Solid State Lithium Batteries Via Thin/Bendable Sulfide Solid Electrolyte Films
May 7th, 2015 by James Ayre
New, high-performance (high energy density + high rate capabilities), completely solid-state lithium batteries have been developed by a team of researchers based out of South Korea.
These new all-solid-state lithium batteries (ASLBs) were created via the use of newly developed bendable/thin sulfide solid electrolyte films which were reinforced with a high performance polymer (paraphenylene terephthalamide/PPTA NW) scaffolding.
These new ASLBs possess a roughly threefold increase in energy density (up to 44 Wh kgcell−1) as compared to conventional all-solid-state cell — still considerably lower than other competing battery technologies currently under development though (see graph below).
The respective first discharge capacities of the SE-NW-SE and pNW-SE-pNW LCO/LTO cells, 85 and 89 mA h gLCO–1, translate to energy density values of 42 and 44 Wh kgcell–1. Figure 4e shows the cell energy density of all-solid-state cells as a function of the overall weight fraction of SE. The energy density obtained in this work (44 Wh kgcell–1) is still much lower than that (100–200 Wh kgcell–1) of commercialized LIBs(52) and also some conventional ASLB adopting high-capacity electrode materials such as sulfur (eg, ∼150 Wh kgcell–1 assuming that Li metal can be used.). It should be noted, however, that by applying the bendable and thin NW-SE film, the energy density of the LCO/LTO ASLB was almost three times higher than that of the conventional ASLB (15 Wh kgcell–1) that does not contain NW.
Here are some more chunks taken from the paper to provide some background:
Spurred by desperate demands for safe LIBs, all-solid-state lithium batteries (ASLBs) using noninflammable inorganic solid electrolytes (SEs) have attracted significant attention as ultimately safe energy storage device. LiPON (Li3.3PO3.9N0.17) is a well-known commercialized SE material and is used to fabricate thin-film-type ASLBs. However, owing to its low room-temperature ionic conductivity in the range of ∼10−6 S cm−1 and high preparation cost via vacuum deposition the application of thin-film-type ASLBs is limited to low energy devices such as smart cards and microelectronics.
In contrast, bulk-type ASLBs in which composite electrodes comprise a mixture of electrode materials, SE particles, and conductive carbon are considered to be fabricated by a scalable process and are especially promising for outperforming the conventional LIBs. … However, sintering at a high temperature of at least ∼800 °C is necessary to form two-dimensional contacts between active materials and oxide SEs. Unfortunately, high-temperature sintering deteriorates the interfaces between active materials and oxide SEs, leading to extremely poor electrochemical performances.
In sharp contrast, promising performances for bulk-type ASLBs have been reported using sulfide SE materials such as glass-ceramic Li2S−P2S5 … Even though sulfide SE materials suffer from instability in air (due to generation of toxic H2S gas when reacting with moisture in air), the investigation of ASLBs using sulfide SEs has been accelerated because sulfide SEs are far superior to their oxide counterparts in terms of the following properties: First, sulfide SEs exhibit higher ionic conductivities than oxide SEs. … Second, the sulfide SE is ductile, exhibiting Young’s moduli in between those of organic polymers and oxide ceramics, which enables intimate contacts with active materials by means of a simple cold pressing procedure.
The new research utilized glass-ceramic Li3PS4 and tetragonal Li10GeP2S12. The scaffolding was, as stated before, PPTA NW — thereby imparting some strength and flexibility to the above-mentioned materials.
The new sulfide electrolyte films reportedly possess lower conductivity values than conventional ones, but owing to the materials used, the bendable composites can be made much thinner than conventional SE films — and reportedly appear to have higher conductance values, when taken in that way.
The new all-solid-state cells utilized LiTiS2 (LTS) in the cathode, and Li4Ti5O12 (LTO) in the anode.
As you can no doubt guess, the researchers involved hold high hopes for their work: “We believe that the NW-SE films proposed herein hold significant promise as a compelling building unit and their combination with the elaborately designed cell architecture provides a new route for the development of high-performance ASLBs.”
As always with battery technology research, though, actual applicability and commercial interest is still something of an open question.
The new research was detailed in a paper just published in the ACS journal Nano Letters. (It can be found here, for those interested — behind a paywall, though).