Solid-State Batteries Get Wet

In the March issue of Joule, Chunsheng Wang, Xiangxin Guo, and collaborators develop a process to form an all-ceramic cathode-electrolyte composite with extremely low interfacial resistance, demonstrating excellent cycling performance in a full solid-state cell with Li metal anode, garnet-type Li7La3Zr2O12 (LLZO) electrolyte, and LiCoO2 (LCO) cathode. By taking advantage of the native Li2CO3 impurity formed on the electrolyte and cathode materials when exposed in ambient conditions, the authors outline a practical process to produce an electrochemically stable and ionically conductive interphase that wets both LLZO and LCO. In the March issue of Joule, Chunsheng Wang, Xiangxin Guo, and collaborators develop a process to form an all-ceramic cathode-electrolyte composite with extremely low interfacial resistance, demonstrating excellent cycling performance in a full solid-state cell with Li metal anode, garnet-type Li7La3Zr2O12 (LLZO) electrolyte, and LiCoO2 (LCO) cathode. By taking advantage of the native Li2CO3 impurity formed on the electrolyte and cathode materials when exposed in ambient conditions, the authors outline a practical process to produce an electrochemically stable and ionically conductive interphase that wets both LLZO and LCO. Driven by continually decreasing cost, the revolution in lithium ion (Li-ion) battery technology is apparently well underway and continues to march along at an accelerated pace, amid much fanfare and mainstream coverage. At the same time, battery scientists are quick to acknowledge that improving upon the performance of current commercial Li-ion cells is an increasingly difficult but necessary endeavor. The looming prospect of hitting a hard limit in the electrochemical performance achievable with the conventional Li-ion cell architecture (Li intercalation-based electrode materials and non-aqueous liquid electrolyte) sits in the minds of many in the field. Accordingly, significant effort has been directed toward investigating a number of alternative, so-called “beyond Li-ion” technologies that have the outside possibility of outperforming Li-ion by employing new chemistries and/or cell architectures. Though each “beyond Li-ion” technology investigated in the literature may present a well-motivated path to realizing breakthroughs in important battery performance metrics, the vast majority of these technologies operate at the earliest stages of development. They often face fundamental technical obstacles that are especially difficult to foresee and resolve. Truthfully, surpassing the performance of a finely tuned energy storage technology as mature as state-of-the-art Li-ion with any radically different alternative is a daunting challenge that still requires large leaps in human ingenuity. Therefore, it comes as a very welcome surprise that batteries with solid-state electrolytes are receiving enthusiastic attention not only from the basic research community, but also from the private sector with recent prominent endorsements from large companies, hopefully a positive sign of market readiness and future deployment.1Shirouzu, N. Toyota scrambles to ready “game-changer” EV battery for mass market. Reuters. October 27, 2017. https://www.reuters.com/article/us-autoshow-tokyo-toyota-battery/toyota-scrambles-to-ready-game-changer-ev-battery-for-mass-market-idUSKBN1CW27Y.Google Scholar, 2Will solid-state batteries power us all? The Economist. October 16, 2017. https://www.economist.com/blogs/economist-explains/2017/10/economist-explains-6.Google Scholar, 3Solid Power, BMW partner to develop next-generation EV batteries. Reuters. December 18, 2017. https://www.reuters.com/article/us-bmw-solid-power/solid-power-bmw-partner-to-develop-next-generation-ev-batteries-idUSKBN1EC16V.Google Scholar For example, Toyota announced its intention to commercialize all solid-state batteries for application in electric vehicles by the early 2020s,1Shirouzu, N. Toyota scrambles to ready “game-changer” EV battery for mass market. Reuters. October 27, 2017. https://www.reuters.com/article/us-autoshow-tokyo-toyota-battery/toyota-scrambles-to-ready-game-changer-ev-battery-for-mass-market-idUSKBN1CW27Y.Google Scholar and BMW recently announced a partnership with solid-state battery company Solid Power, also to pursue application in electric vehicles.3Solid Power, BMW partner to develop next-generation EV batteries. Reuters. December 18, 2017. https://www.reuters.com/article/us-bmw-solid-power/solid-power-bmw-partner-to-develop-next-generation-ev-batteries-idUSKBN1EC16V.Google Scholar The excitement could be well warranted, as the full promise of all solid-state batteries is certainly nothing short of a breakthrough.4Janek J. Zeier W.G. A solid future for battery development.Nat. Energy. 2016; 1: 16141Crossref Scopus (1641) Google Scholar, 5Sun C. Liu J. Gong Y. Wilkinson D.P. Zhang J. Recent advances in all-solid-state rechargeable lithium batteries.Nano Energy. 2017; 33: 363-386Crossref Scopus (1098) Google Scholar, 6Luntz A.C. Voss J. Reuter K. Interfacial challenges in solid-state Li ion batteries.J. Phys. Chem. Lett. 2015; 6: 4599-4604Crossref PubMed Scopus (319) Google Scholar Replacing the flammable liquid electrolyte with a solid Li-ion conducting medium could mostly mitigate costly safety risks (also reduce the need for additional system management7Lu L. Han X. Li J. Hua J. Ouyang M. A review on the key issues for lithium-ion battery management in electric vehicles.J. Power Sources. 2013; 226: 272-288Crossref Scopus (3312) Google Scholar), and simultaneously present new routes to high energy density by enabling the use of electrode materials and cell designs previously incompatible with liquid electrolytes. While replacing the non-aqueous liquid electrolyte with a solid Li-ion conductor has its benefits, it also introduces a host of new complications and design considerations, the majority of which are focused at the active electrode interfaces in the cell.8Kerman K. Luntz A. Viswanathan V. Chiang Y.M. Chen Z. Practical Challenges Hindering the Development of Solid State Li Ion Batteries.J. Electrochem. Soc. 2017; 164: A1731-A1744Crossref Scopus (429) Google Scholar, 9Wu B. Wang S. Evans IV, W.J. Deng D.Z. Yang J. Xiao J. Interfacial behaviours between lithium ion conductors and electrode materials in various battery systems.J. Mater. Chem. A Mater. 2016; 4: 15266-15280Crossref Google Scholar In conventional Li-ion cells, the non-aqueous liquid electrolyte not only possesses high ionic conductivity, but critically, it also forms dynamic but robust electrochemically active interfaces stable against the electrode materials and enables a more than 4 V operating voltage window. The same functionality must be accomplished in solid-state batteries, but maintaining high-fidelity interfaces becomes even more problematic when all components are now solid materials. Also, secondary phases formed during processing or electrochemical operation can introduce unwanted interfacial impedance, which is difficult to negotiate as well. In the March issue of Joule, Chunsheng Wang, Xiangxin Guo, and collaborators10Han F. Yue J. Chen C. Zhao N. Fan X. Ma Z. Gao T. Wang F. Guo X. Wang C. Interphase Engineering Enabled All-Ceramic Lithium Battery.Joule. 2018; 2 (Published online February 28, 2018)https://doi.org/10.1016/j.joule.2018.02.007Abstract Full Text Full Text PDF Scopus (304) Google Scholar develop a process to form an all-ceramic cathode-electrolyte composite with extremely low interfacial resistance, demonstrating excellent cycling performance in a full solid-state cell with Li metal anode, garnet-type Li7La3Zr2O12 (LLZO) electrolyte, and LiCoO2 (LCO) cathode. By taking advantage of the native Li2CO3 impurity formed on the electrolyte and cathode materials when exposed in ambient conditions, the authors outline a practical process to produce an electrochemically stable and ionically conductive interphase that wets both LLZO and LCO. In 2007, Murugam, Thangadurai, and Weppner introduced Li7La3Zr2O12 (LLZO) as a top solid electrolyte candidate, with suitable ionic conductivity, compatibility with Li metal, and air stability.11Murugan R. Thangadurai V. Weppner W. Fast lithium ion conduction in garnet-type Li(7)La(3)Zr(2)O(12).Angew. Chem. Int. Ed. 2007; 46: 7778-7781Crossref PubMed Scopus (2089) Google Scholar Unfortunately, it is exceptionally difficult to prepare LLZO/LCO electrodes without also introducing a number of secondary electronically resistive phases when in contact, either in the sintering process or during electrochemical operation. One strategy is to keep LLZO and LCO entirely separated. By designing Li2.3C0.7B0.3O3 to ultimately react with the Li2CO3 accumulated on the LLZO and LCO particle’s surface, the authors ensured cathode and electrolyte particles never touch but do form in between a fast ion conducting interphase, Li2+yC1-yByO3 (y = 0∼0.3). With this approach, they were able to prepare cells with an initial ∼120 mAh/g capacity, tapering to 57 mAh/g after 50 cycles at 0.05 C at 100°C. At room temperature, impressive capacity was achieved for over 100 cycles, further demonstrating the viability of the approach. In future work, Wang and Guo aim to address the capacity decay especially at high temperature, which they attribute to mechanical degradation of the cathode/electrolyte interface arising from the repetitive cathode volume change. The authors suggest that this could be addressed potentially using LLZO nanowires acting as a reinforcing phase improving the mechanical strength of the cathode. Interphase Engineering Enabled All-Ceramic Lithium BatteryHan et al.JouleFebruary 28, 2018In BriefAll-ceramic cathode-electrolyte with a low interfacial resistance can be realized by thermally soldering LiCoO2 and Li7La3Zr2O12 (LLZO) together with Li2.3−xC0.7+xB0.3−xO3 solid electrolyte interphase through the reaction between the Li2.3C0.7B0.3O3 solder and the Li2CO3 layers that can be spontaneously coated on both LLZO and LiCoO2. The all-solid-state Li/LLZO/LiCoO2 battery with such an all-ceramic cathode/electrolyte exhibits high cycling stability and high rate performance. Full-Text PDF Open Archive