Advanced Microscopy and Spectroscopy for Probing and Optimizing Anionic Redox in High Energy Lithium Batteries
The earliest developed LiCoO2 layered oxide cathode material sparked the development of other layered cathode materials, dominating the positive electrode materials for lithium ion batteries. Within the practical operating conditions of today, the current generation layered oxide materials do not meet the future energy storage demands of 350 Wh kg-1 per cell. This roughly translates to over 800 Wh kg-1 at the positive electrode level. Li-excess materials have the potential to meet the high energy demands. Unlike the classical layered oxides, Li-excess materials exhibit capacities that go beyond conventional topotactic mechanistic theoretical values because of reversible and stable anionic redox.
In the past five years, our research group has made great progress on developing advanced characterization techniques (including coherent X-ray imaging, neutron pair distribution function, and resonant inelastic X-ray scattering) coupled with atomic scale modeling to properly characterize the dynamic phenomena that govern the anionic redox related performance limitations of Li-excess materials. Furthermore, our efforts have improved the material synthesis and surface modification to improve capacity retention. It is through the in-depth understanding of these anionic redox based cathode materials at atomistic and molecular level and their dynamic changes during the operation of batteries; we can successfully formulate strategies to optimize this class of cathode materials.
1. A. Singer, M. Zhang, S. Hy, D. Cela, C. Fang, T. A. Wynn, B. Qiu, Y. Xia, Z. Liu, A. Ulvestad, N. Hua, J. Wingert, H. Liu, M. Sprung, A. V. Zozulya, E. Maxey, R. Harder, Y. S. Meng, and O. G. Shpyrko,”Nucleation of Dislocations and Their Dynamics in Layered Oxide Cathode Materials During Battery Charging‘ ,Nature Energy, 2018, 3, 641
2. B. Qiu, M. Zhang, L. Wu, J. Wang, Y. Xia, D. Qian, H.D. Liu, S. Hy, Y. Chen, K. An, Y. Zhu, Z. Liu, Y. S. Meng, “Gas–solid interfacial modification of oxygen activity in layered oxide cathodes for lithium-ion batteries“, Nature Communication 2016, 7,12108
3. Sunny Hy, H.D. Liu, M. Zhang, D. Qian, B.-J. Hwang, Y. S. Meng, “Performance and design considerations for lithium excess layered oxide positive electrode materials for lithium ion batteries“, Energy & Environmental Science, 2016, 9, 1931
Co Free Cathode Materials and Their Novel Architectures
The next generation Li-ion batteries (LIBs) need reasonable matching of electrode and electrolyte to achieve the best performance, including longer cycling and better safety. For the cathode materials, the current commercialization and research mainly focuses on lithium metal oxides (LiNixCoyMnzO2, x+y+z=1) with layered structure. Layered lithium metal oxides have high energy densities, but the use of expensive and toxic cobalt elements greatly restricts their application in widespread commercialization of electric vehicles. In this context, a new spinel type oxide LiNi0.5Mn1.5O4 (LNMO) is of great focus with a theoretical capacity of 147 mAh/g and average working voltage as high as 4.7 V. More importantly, it does not contain expensive cobalt, which makes LNMO cathode cost-effective and suitable for applications in the field of power batteries and large-scale energy storage.
The objective of this project is to research, develop, and demonstrate a spinel type LNMO electrode and novel electrolyte formulation for use in next-generation LIBs. Our proposed cathode is 100% free of cobalt and its novel architecture will have porosity less than 20% and designed tortuosity for high rate capability. In addition, to guide our research to determine which electrolyte system is more stable and compatible for LNMO electrode materials under high voltage cycling, we will develop a series of characterization techniques such as ex-situ X-ray photoelectron spectroscopy (XPS), ex-situ cryogenic transmission electron microscopy (cryo-TEM), ex-situ cryogenic focused ion beam microscope (cryo-FIB) and in situ time-of-flight secondary-ion mass spectrometry (TOF-SIMS).
J. Alvarado, M. A. Schroeder, M. Zhang, O. Borodin, E. Gobrogge, M. Olguin, M. S. Ding, M. Gobet, S. Greenbaum, Y. S. Meng, K. Xu, “A carbonate-free, sulfone-based electrolyte for high-voltage Li-ion batteries” “supplementary data” Materials Today, 2018, 21(4), 341
The lithium metal subgroup focuses on the lithium metal anode fundamental materials science aiming to enable next-generation high-energy lithium metal batteries. The research area of the lithium metal subgroup includes but not limited to investigating the lithium metal failure mechanism from chemical, physical and mechanical perspectives, designing strategies to improve lithium metal performances, including designing novel electrolytes and 3D current collectors. A variety of state-of-the-art characterization tools are utilized, including Titration Gas Chromatography1, Cryogenic Electron Microscope, Cryogenic Focused Ion Beam, etc. The lithium metal subgroup currently has three Ph.D. students, Chengcheng Fang, Bingyu Lu, Yihui Zhang, and one undergraduate student Miguel Ceja.The cause and solution for the Li metal problems. The continuous formation of inactive Li is the direct cause of low CE, safety hazards and cell expansion in Li metal batteries. Li whiskers with large tortuosity and heterogeneous SEI will facilitate the inactive Li formation and cause the series of problems; whereas if the deposited Li possesses a chunky morphology with minimal tortuosity and homogeneous SEI, the inactive Li formation will be significantly reduced, resulting in high CE.
1. C. Fang et al. Quantifying Inactive Lithium in Lithium Metal Batteries. in press. (2019)
2. C.Fang, X.Wang, and Y. S. Meng, “Key Issues Hindering a Practical Lithium-Metal Anode” Trends in Chemistry, 2019, 1, 152
In many applications, energy density and low-temperature performance are two key metrics that state-of-the-art Li-ion batteries have significant difficulty meeting. In recent years, a lot of focus has been placed on the use of the Li-metal anode in combination with high voltage cathodes to dramatically increase the energy densities of batteries. Actual use of these systems has been hampered due to the unavailability of electrolytes that are compatible with the Li-metal anode while at the same time resistant to degradation at the high voltage cathode. Our liquefied gas electrolyte work focuses on gases that are promising candidates to achieve the stability required at both the anode and cathode in these aggressive, high voltage systems. At low temperatures or moderate pressures, these gases liquefy and can dissolve lithium salts to form liquefied gas electrolytes. These electrolytes have shown impressive compatibility with the Li-metal anode, and very good stability with high voltage cathodes as well as dramatically improved low temperature performance down to -60C.
Through experimental and computational approaches, our research has focused on the interesting solvation and transport mechanisms of the bulk electrolyte as well as the interfaces formed on both anodes and cathodes. Our work has opened a new area of research in the energy storage field and we hope to see new materials and manufacturing methods developed from the idea of using these gaseous solvents.
1. Y. Yang, D. M. Davies, Y. Yin, O. Borodin, J. Z. Lee, C. Fang, M. Olguin, X. Wang, Y. Zhang, E. S. Sablina, C. S. Rustomji, Y. M. Meng, “High Efficiency Lithium Metal Anode Enabled by Liquefied Gas Electrolytes “, Joule, 2019, in press
2. C. S. Rustomji, Y. Yang, T. K. Kim, J. Mac, Y. J. Kim, E. Caldwell, H. Chung, Y. S. Meng, “Liquefied Gas Electrolytes for Electrochemical Energy Storage Devices“, Science, 2017, 356, 1351
With the invention of non-aqueous electrolytes which enabled the use of alkali metal anodes, the energy density of batteries exhibited a remarkable improvement. However, in order to mitigate the safety issues the energy density was compromised and Li ion batteries (LIBs) were designed and got wide popularity especially in the potable electronic market. Fast approaching saturation curves of LIB performance matrices and pressing demands for higher energy and power density energy storage systems to support high energy demanding applications viz. electric vehicles make a situation inevitable to stretch out beyond LIBs. Revisiting Li metal anodes as in Li-O2 non-aqueous chemistry seems to be promising even though the understanding of the mechanism is in its infancy. Major bottle neck of exploiting the reversible reaction between Li+ and O2 is the sluggish kinetics of the electrochemical decomposition of the discharge product viz. Li2O2 to Li+ and O2 (Oxygen Evolution Reaction-OER). Fundamental understanding of Li-O2 electrochemistry is believed to pave way for other alkali Metal-Air batteries.
Various approaches aiming to improve the kinetic requirements of the fast charge/discharge include, addition of redox mediators, solubilizing agents etc. Carbonaceous matrices have been nanoengineered to facilitate the discharge process (Oxygen Reduction Reaction-ORR) and mass transport, thus currently playing pivotal role beyond just as catalyst support layer. Our recent oxyhalogen-sulfur electrochemistry approach synergistically combines these two and the round-trip efficiency is remarkably improved. Multi-faceted approaches to take control over the nucleation site, size and composition of the discharge products is critical in the design and fabrication of a practically usable Metal-Air battery.
Schematic depicting the mechanism of oxyhalogen-sulfur electrochemistry driven charge discharge processes
X. Wang, Y. Li, X. Bi, L. Ma, T. Wu, M. Sina, S. Wang, M. Zhang, J. Alvarado, B. Lu, A. Banerjee, K. Amine, J. Lu, and Y. S. Meng “Hybrid Li-Ion and Li-O2 Battery Enabled by Oxyhalogen-Sulfur Electrochemistry“, Joule. 2018, 2, 11, 2381
Research into inexpensive, long lifetime, grid energy storage options is increasingly important as we move to sustainable energy sources such as solar and wind. Sodium ion batteries are an exciting, inexpensive option for grid storage. The components of sodium ion batteries can be made with inexpensive elements such as manganese, iron, and carbon. While initial results show that sodium ion batteries have relatively high energy density, improvements in energy density and lifetime are necessary to make them a viable option.
To improve sodium ion batteries energy density and lifetime, we are studying the mechanism of energy storage in both the cathode and anode including material degradation and irreversible reactions. We use the many tools at our disposal, including novel synthesis methods and advanced characterization techniques. These advanced characterization techniques (XRD, TEM, FIB, NMR, synchrotron instruments, etc.) allow us to “see” what is happening inside the battery from atomic to macro scale. On the cathode side we are researching the irreversible reactions in high capacity inexpensive materials and how to increase the capacity by utilizing oxygen redox. On the anode side we are studying the irreversible reactions and how to increase their life time. We aim to determine the mechanism of energy storage in sodium ion batteries and use this knowledge to build better ones.
1. H. Li, H. Tang, C. Ma, Y. Bai, J. Alvarado, B. Radhakrishnan, S. P. Ong, F. Wu, Y. S. Meng, and C. Wu “Understanding the Electrochemical Mechanisms Induced by Gradient Mg2+ Distribution of Na-Rich Na3+xV2–xMgx(PO4)3_C for Sodium Ion Batteries” Chem. Mater., 2018, 30 (8), 2498
2. M. D. Radin, J. Alvarado, Y. S. Meng, and A. V. der Ven “Role of Crystal Symmetry in the Reversibility of Stacking-Sequence Changes in Layered Intercalation Electrodes”,Nano Letters, 2017, 17(12), 7789
3. J. Alvarado, C. Ma, S. Wang, K. Nguyen, M. Kodur, and Y. S. Meng, “Improvement of the Cathode Electrolyte Interphase on P2-Na2_3Ni1_3Mn2_3O2 by Atomic Layer Deposition“ACS Appl. Mater. Interfaces, 2017, 9(31), 26518
4. C. Ma, J. Alvarado, J. Xu, R. J. Clément, M. Kodur, W. Tong, C. P. Grey, and Y. S. Meng,”Exploring Oxygen Activity in the High Energy P2-Type Na0.78Ni0.23Mn0.69O2 Cathode Material for Na-Ion Batteries“, J. Am. Chem. Soc., 2017, 139(13), 4835
Hybrid organic-inorganic perovskite materials, expressed as ABX3 where a monovalent cation (such as methylammonium (CH3NH3+), formamidinium (CH(NH2)2+), and Cesium (Cs+)) are located at A site, Sn or Pb is located at B site, and halide (I–/Br–/Cl–) is placed at X site, have been attained a lot of attention for their photovoltaic applications. Perovskite materials have great properties as high absorption coefficient, tunable bandgap, low exciton binding energy and long carrier diffusion length, thereby perovskite solar cells (PSCs) are now exhibiting greatly high power conversion efficiencies up to 24.2 % which is comparable performance to conventional polycrystalline Silicon photovoltaics. Though PSCs are close to Si photovoltaics, they still have some drawbacks as their humid/thermal instability, small scale and use of toxic Pb materials. Especially, long-term stability and large-area production should be achieved to take over Si photovoltaics role as a primary conventional solar cell.
So far, we achieved to elucidate the working mechanisms of hole transport materials and degradation process of PSCs. With the help of advanced characterizations like FIB-TEM, APT, and STEM-EELS, we were able to deeply understand their charge transfer and recombination mechanisms. Based on previous researches, we are now aiming for the commercialization of PSCs by scaling up and enhancing long-term stability of the PSCs. Device encapsulation or compositional engineering can provide better stability of PSCs and by developing efficient large-area producing method rather than spin-coating method, we can achieve large-area production of PSCs.
1.S. Wang, Z. Huang, X. Wang, Y. Li, M. Günther, S. Valenzuela, P. Parikh, A. Cabreros, W. Xiong, and Y. S. Meng “Unveiling the Role of tBP−LiTFSI Complexes in Perovskite Solar Cells” J.Am.Chem.Soc 2018, 140 (48), 16720
2. S. Wang, M. Sina, P. Parikh, T. Uekert, B. Shahbazian, A. Devaraj, and Y. S. Meng, “Role of 4-tert-Butylpyridine as a Hole Transport Layer Morphological Controller in Perovskite Solar Cells” Nano Letters, 2016, 16, 5594
3. S. Wang, W. Yuan, and Y. S. Meng. “Spectrum-Dependent Spiro-OMeTAD Oxidization Mechanism in Perovskite Solar Cells“, ACS Appl. Mater. Interfaces, 2015, 7 (44), 24791
Silicon anode subgroup is involved towards developing the next generation of alloy anodes to replace graphite, for increased cell energy density. Silicon anodes can provide high theoretical specific capacity (~4000 mAh/g) but suffer from large volume expansion (~300%) and subsequent contraction during lithiation and delithiation, that severely affects its capacity retention. Our efforts are geared towards solving this fundamental issue through binder engineering, pre-lithiation strategies and exploring silicon oxide as an alternative solution for stable capacity retention. Our team explores the realm of both half-cell and full cell configurations to understand the effects that arise from both the anode and cathode.
Our expertise in diagnosing battery materials through advanced characterization, using tomography for 3-D visualization, microscopy and spectroscopy (TEM, XPS) and electrochemistry provides us with a deeper understanding of the issues and help us to provide more targeted and effective solution to current challenges.
1. P. Parikh, M. Sina, A. Banerjee, X. Wang, M. Savio D’Souza, J.-M. Doux, E. A. Wu, O. Y. Trieu, Y. Gong, Q. Zhou, K. Snyder, and Y. S. Meng, “Role of Polyacrylic Acid (PAA) Binder on the Solid Electrolyte Interphase in Silicon Anodes” Chemistry of Materials, 2019, 31 (7), 2535
2. H. Shobukawa, J. Alvarado, Y. Yang, Y. S. Meng, “Electrochemical performance and interfacial investigation on Si composite anode for lithium ion batteries in full cell”, Journal of Power Sources, 2017, 359, 173
3. M. Sina, J. Alvarado, H. Shobukawa, C. Alexander, V. Manichev, L. Feldman, T. Gustafsson, K. Stevenson, Y. S. Meng,”Direct Visualization of the Solid Electrolyte Interphase and Its Effects on Silicon Electrochemical Performance” Adv. Mater. Interfaces 2016, 1600438
4. H. Shobukawa, J.W. Shin, J. Alvarado, C. S. Rustomji and Y. S. Meng, “Electrochemical reaction and surface chemistry for performance enhancement of a Si composite anode using a bis(fluorosulfonyl)imide-based ionic liquid”, Journal of Materials Chemistry A., 2016, 4, 15117
1. H. Nguyen, S. Hy, E. Wu, Z. Deng, M. Samiee, T. Yersak, J. Luo, S. P. Ong, Y. S. Meng, “Experimental and Computational Evaluation of a Sodium-Rich Anti-Perovskite for Solid State Electrolytes”, Journal of The Electrochemical Society, 2016, 163(10), A2165
2. I.-H. Chu, H. Nguyen, S. Hy, Y.-C. Lin, Z. Wang, Z. Xu, Z. Deng, Y. S. Meng, and S. P. Ong, “Insights into the Performance Limits of the Li7P3S11 Superionic Conductor_ A Combined First-Principles and Experimental Study“, ACS Appl. Mater. Interfaces, 2016, 8 (12), 7843
3. I.-H. Chu, C. S. Kompella, H. Nguyen, Z. Zhu, S. Hy, Z. Deng, Y. S. Meng and S. P. Ong “Room-Temperature All-solid-state Rechargeable Sodium-ion Batteries with a Cl-doped Na3PS4 Superionic Conductor”, Scientific Reports, 2016, 6, 33733
4. E. A. Wu, C. S. Kompella, Z. Zhu, J. Z. Lee, S. C. Lee, I.-H. Chu, H. Nguyen, S. P. Ong, A. Banerjee, and Y. S. Meng,”New Insights into the Interphase between the Na Metal Anode and Sulfide Solid-State Electrolytes_ A Joint Experimental and Computational Study” ACS Appl. Mater. Interfaces, 2018, 10 (12), 10076
All-solid-state batteries (ASSB) offer high energy density and are a safer alternative to conventional liquid electrolytes commonly used in Li-ion batteries. However, electrolyte selection is limited, and those exhibiting competitive ionic conductivities often exhibit high interfacial impedances. Thin film batteries are ASSBs with thickness of only a few micrometers, which have the benefits of solid-state batteries with the potential to be incorporated in microelectronics. Further, they provide with ideal platforms for interfacial studies due to their well-defined geometries.
Thin film subgroup in LESC have been exploring new thin film battery compositions and their interfaces including cathodes LiCoO2 (LCO) and LiNi0.5Mn1.5O4 (LNMO), electrolytes including lithium phosphorus oxynitride (LiPON) and novel amorphous electrolyte lithium lanthanum titanate (LLTO), and anodes of amorphous Si and Li-metal.
Novel characterization technique developed by thin film subgroup has enabled galvanostatically cycling nanobatteries within a TEM for in situ study of interfacial phenomena. Recently, we have also developed high quality cross-sectional analysis combining cryogenic FIB with three-dimensional slice-and-view, allowing high quality quantitative analysis of plating behavior of alkali metal anodes. For future work, thin film subgroup will combine cryogenic focused ion beam and cryogenic TEM for the in situ study of Li metal/solid-state electrolyte and solid-state electrolyte/ cathode interfaces.
1. J. Z. Lee, T. A. Wynn, M. A. Schroeder, J. Alvarado, X. Wang, K. Xu, and Y. S. Meng, “Cryogenic Focused Ion Beam Characterization of Lithium Metal Anodes“ ACS Energy Letters, 2019, 4, 489
2. J. Z. Lee, T. A. Wynn, Y. S. Meng, D. Santhanagopalan, “Focused Ion Beam Fabrication of LiPON-based Solid-state Lithium-ion Nanobatteries for In Situ Testing” . J. Vis. Exp, 2018, e56259
3. J. Z. Lee, Z. Wang, H. L. Xinb, T. A. Wynn, and Y. S. Meng, “Amorphous Lithium Lanthanum Titanate for Solid-State Microbatteries“, Journal of The Electrochemical Society, 2017, 164(1), 6268
4. Z. Wang, D. Santhanagopalan, W. Zhang, F. Wang, H. L. Xin, K. He, J. Li, N. Dudney, and Y. S. Meng,”In Situ STEM-EELS Observation of Nanoscale Interfacial Phenomena in All-Solid-State Batteries“, Nano Letters, 2016, 16 (6), 3760
Attributed as the first practical battery developed, Zinc-anode batteries have the known benefits of low material cost, non-toxicity, and a relatively high theoretical energy density. Zinc-based batteries are commercially implemented in the medical and stretchable electronics industry and have great promise in grid storage. In our lab, we use advanced characterization tools such SEM (Figure 1), XRD, and XPS to understand, synthesize, and develop better batteries to power the world.
Figure 1 Example of using Scanning Electron Microscopy to identify degradation mechanism in Zn-Ag batteries
Printable Stretchable Zn-Based Batteries
Owing to their high energy and power densities (Figure 2), rechargeability, and low-cost, Zinc-Silver (Zn-Ag) batteries offer excellent features to power flexible, stretchable, and wearable electronic devices. With academic and industrial collaboration, our lab has demonstrated the ability to print high throughput stretchable energy dense batteries.
Figure 2 Energy density vs. specific energy showing comparison of commercial versus Ag-Zn batteries
Figure 3 Example of printed stretchable Zn battery
R. Kumar, J. Shin, L. Yin, J.-M. You, Y. S. Meng, Joseph J Wang, “All-Printed, Stretchable Zn-Ag2O Rechargeable Battery via, Hyperelastic Binder for Self-Powering Wearable Electronics“, Advanced Energy Materials, 2017, 1602096
The Computational Materials Science Group at LESC uses atomistic scale modeling to provide predictive understanding of Li-ion battery materials physicochemical properties.
We employ highly accurate first-principles and classical molecular dynamics techniques to study the electronic structure and energetics of anode, bulk electrolyte, cathode, and interface systems on massively parallel supercomputers. These computational chemistry approaches are performed in close collaboration with experimentalists via a complimentary research strategy with the aim of designing functional state-of-the-art battery materials.
1. Y. S. Meng, M. E. A.-d. Dompablo, (invited review) “First principles computational materials design for energy storage materials in lithium ion batteries“, Energy & Environmental Science, 2009, 2, 589
2. B. Xu, C. R. Fell, M. Chi, and Y. S. Meng, “Identifying surface structural changes in layered Li-excess nickel manganese oxides in high voltage lithium ion batteries: A joint experimental and theoretical study“, Energy & Environmental Science, 2011, 4, 2223
3. T. A. Wynn, C. Fang, M. Zhang, H. Liu, D. M Davies, X. Wang, D. Lau, J. Z Lee, B.-Y. Huang, K. Z. Fung, C.-T. Ni and Y. S. Meng “Mitigating Oxygen Release in Anionic-Redox-Active Cathode Materials by Cationic Substitution through Rational Design” JMCA 2018, 6, 24651
4. I.-H. Chu, M. Zhang, S. P. Ong, and Y. S. Meng, “Handbook of Materials Modeling-Battery Electrodes, Electrolytes, and Their Interfaces“
Among other low cost energy storage alternatives to Li-ion batteries, the Meng group explores several flow battery chemistries. Chief among them has been the soluble lead flow battery (SLFB). Social perception of lead-based products is extremely negative due to their association with an array of adverse health effects. The traditional lead-acid battery is the most highly recycled product on earth, however, trumping tires, paper, aluminum cans, and glass. Through centuries of use, we have had time to very thoroughly discern the harmful impacts of these materials, as well as methods to circumvent those negative aspects. A vast infrastructure currently exists to manufacture and sustainably maintain lead-acid batteries, arguably making them the cheapest and most realistic option to implement into grid-level energy storage today, without perverting the market with unsustainable government subsidy.
Much like the traditional lead-acid battery, SLFB chemistry incorporates the reaction of lead (Pb) and lead oxide (PbO2) at anode and cathode, respectively. Unlike traditional lead-acid, however, no sulfuric acid is used in the electrolyte. No sulfate-based products are generated, therefore, overcoming a major deterioration mechanism. By flowing electrolyte through the battery during operation, power and energy components are separated, making large-scale design efficient and flexible. Compared to other flow battery technologies SLFBs provide the added advantage of having a single electrolyte and no separator. Balance of plant is, therefore, considerably less expensive than other chemistries, including its traditional lead-acid predecessor. While the price point is markedly better than competing technologies, performance is not. Power density and cycle life in particular are much lower than technologies such as vanadium-redox. Our group has made progress improving upon these shortcomings, but current research aims to get better still.
1. A. Orita, M. G. Verde, M. Sakai, and Y. S. Meng “A biomimetic redox flow battery based on flavin mononucleotide“, Nat. Commun., 2016, 7, 13230
2. A. Orita, M.G. Verde, M. Sakai, Y.S. Meng,”The impact of pH on side reactions for aqueous redox flow batteries based on nitroxyl radical compounds“, Journal of Power Sources., 2016, 324, 342