Advanced Lithium Batteries for Automobile Applications at ABAA-9

Advanced Lithium Batteries for Automobile Applications at ABAA‑9

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consortium will improve the electrode architecture and cell design to ensure significant innovations that can be quickly and seamlessly implemented by industry throughout the project. New Innovative Research Projects proposed by others from throughout the battery research community will be added each year as “Seedlings” for diversity in experience and opinions. Shuguang Bian, Deputy Director of the High Technology R&D Center, Ministry of Science and Technology (MOST) of the People’s Republic of China, introduced the Clean Energy Vehicle project of the National 13th Five-year Plan (year 2016 to 2020), aiming at lithium batteries with an energy density higher than 300 Wh/kg and cost lower than 0.8 RMB/Wh, as well as beyond-Li battery systems with energy density higher than 500 Wh/kg. Awards totaling 64 million RMB will be given to research institutes and universities for fundamental and frontier investigations of novel materials and new system design, and a 290 million RMB fund is proposed to support high-energy battery technology development led by battery manufacturers. Katsunori Kodato, an officer of the New Energy and Industrial Technology Development Organization (NEDO) of Japan, introduced NEDO’s smart community activities and battery R&D strategies. Novel electrode and electrolyte materials are key in the pursuit of batteries with high energy, high power, long cycle life, good safety, and low cost. On the cathode side, Prof. Stanley Whittingham from SUNY Binghamton discussed their initial results using the model compound VOPO4 for a two-electron redox process, that is, to intercalate two Li ions into a host lattice. This multielectron intercalation cathode delivered a reversible capacity of about 240 mAh/g in cycling from 1.6 to 4.5 V, which is believed to be a promising option for highenergy-density batteries. Dr. Michael Thackeray from Argonne National Laboratory discussed recent advances in designing lithium- and manganese-rich “layered−layered” xLi2MnO3·(1− x)LiMO2 (M = Mn, Ni, Co) cathode materials by seeking a compromise between capacity, cycling stability, and voltage fade. They found that control of the composition and the spinel content in layered−layered spinel cathode structures can enhance the capacity of the electrode, while regulating the electrochemical voltage window of the cells can significantly reduce voltage fade. The charging/discharging rate is a key parameter that dictates how fast energy can be harnessed or released and is critical for applications such as vehicle electrification and renewable energy grids. Prof. Feng Pan from Peking University presented their studies on the kinetics of Li-ion diffusion for two representative cathode materials, layered Li(NixMnyCoz)O2 (NMC) (x + y + z = 1) and LiFePO4 across the bulk electrode, at the electrode/electrolyte

he battery-electrified vehicle industry is booming since the past decade, driven by consumers’ growing demand for “green” cars with zero emission of greenhouse gases and speedy-but-silent driving experience. Aiming for advanced battery technology to support electric vehicles, the International Conference on Advanced Lithium Batteries for Automobile Applications (ABAA) was launched in 2008. It was conceived with the mission of promoting global R&D of automobile lithium batteries through international communication and collaboration engaging automobile manufacturers, battery manufacturers, research institutes, and universities. The ninth International Conference on Advanced Lithium Batteries for Automobile Applications (ABAA-9), held at Sheraton Huzhou Hop Spring Resort on October 17−20, 2016 was coorganized by the International Automotive Lithium Battery Association (IALB) and Huzhou Economic & Technological Development Zone Administrative Committee (see Figure 1). Huzhou, located right at the heart of the Yangtze River Delta Economic Area, is a picturesque city of south China with a history that can be traced back before the Qin Dynasty (about 248 B.C.). With such a long history of harmony between humans developing and the environment, this city is devoted to sustainable development and provides full support to environmentally benign industries, especially battery-electrified vehicles. In the 3.5 day conference, over 50 government officers, world-class leading scientists, and industry leaders from around the world were invited to give talks on the latest research and development in advanced lithium batteries focused on automotive applications, which are critical to achieve fuelefficient automobiles such as hybrid electrical vehicles (HEVs), plug-in hybrid electric vehicles (PHEVs), and pure electric vehicles (EVs). Government officers from the United States, China, and Japan introduced the progress and funding plans of EV battery R&D in the three countries. Dr. Dave Howell, the Acting Director of the Vehicle Technologies Office in the Office of Energy Efficiency and Renewable Energy (EERE) at the U.S. Department of Energy (DOE), presented rapid growth in annual U.S. plug-in electric vehicle sales and shared the vision of the United States Advanced Battery Consortium (USABC) of future battery technology. Advancing the development of batteries is projected to reduce the production cost of an EV battery to $80/kWh, in order to enable a large-market penetration of HEVs and EVs. Dr. Howell also introduced the VTO Battery 500 Consortium, whose strategic goal is to develop and demonstrate cells with a specific energy of 500 Wh/kg and achieving 1000 cycles. The consortium team, including four National laboratories, five universities, and four advisors in the United States, hopes to reach high energy density by focusing on lithium batteries with lithium metal as the anode and two different materials (high nickel NMC and sulfur) as the cathode. While studying these materials, the © XXXX American Chemical Society

Received: May 13, 2017 Accepted: May 31, 2017

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http://pubs.acs.org/journal/aelccp

Energy Focus

ACS Energy Letters

Figure 1. Opening ceremony of the ninth International Conference on Advanced Lithium Batteries for Automobile Applications (ABAA-9), held at Sheraton Huzhou Hop Spring Resort, Huzhou, China, on October 17−20, 2016.

cells”, in which Li metals are used as the counter electrodes, and thus, the Li supply can be considered to be unlimited. Instead, Prof. Dominique Guyomard from the Institute of Materials Jean Rouxel at Nantes and his group focused on the failure mechanisms of the Si electrode in full Li-ion batteries, in which limited Li ions are provided by the cathode. Upon cycling, an inorganic layer of SEI grows at the early stages, while the reductive decomposition of the organic solvents occurs continuously over the cycling. After almost all of the active Li ions from the cathode are trapped in the SEI layer and anode (so-called “dead Li”) upon long cycling, Li-free decomposition of the carbonate solvents goes on and thickens the SEI layer with a degradation mechanism different from that of the half cell. As to the electrolyte, despite many advantages of the water molecule as an excellent solvent (high dielectric constant, strong solvating power, high fluidity, and nonflammability), this narrow stability window of aqueous electrolytes precludes the use of aqueous electrolytes in advanced battery chemistries, especially Li-ion batteries, because the most interested electrochemical couples (cathodes and anodes) reside outside of this narrow range. Dr. Kang Xu from the U.S. Army Research Laboratory succeeded in expanding the thermodynamic stability window of aqueous electrolytes from 1.23 to 3.0 V through the formation of an electrode/electrolyte interphase in aqueous media. Prof. Atsuo Yamada from the University of Tokyo discovered a room-temperature hydrate melt of Li salts as a stable aqueous electrolyte, in which all water molecules participate in Li+ hydration shells with retaining fluidity. The hydrate melt electrolyte enabled the reversible reaction of a commercially used negative electrode, spinel Li4Ti5O12 with a low reaction potential and high capacity. This discovery paves the way for a new class of high-energy-density aqueous Li-ion batteries with over 150 Wh kg−1 and a ∼3.1 V average voltage, making significant inroads in the realm of commercial nonaqueous batteries (150−400 Wh kg−1). The safety evaluation and diagnose of the Li-ion battery is critical for practical application in vehicles. Prof. Liquan Chen from the Institute of Physics of the Chinese Academy of

solid−liquid interface, and in the electrolytes. They proposed that a “Janus” solid−liquid interface would facilitate the Li-ion transport and that introducing some disordering in nonactive cathode materials would activate them for Li-ion storage. On the anode side, silicon (Si) has the potential to revolutionize the energy storage capacity of Li-ion batteries to meet the ever-increasing power demands of next-generation technologies. However, the dramatic volume and structure variation associated with the dynamic formation and decomposition of a solid electrolyte interphase (SEI) layer during Si electrode cycling results in rapid performance degradation. In order to conquer these critical obstacles, Prof. Zhongwei Chen from the University of Waterloo and his group systematically studied the degradation mechanism and innovatively proposed a series of design strategies for the development of highperformance Si-based electrodes. These strategies include preparation of Si−carbon nanocomposites in which Si nanoparticles are shielded within a sponge-like 3D architecture of carbon-based materials; design of the electrode structure from the molecular level, where Si nanoparticles are covalently bonded to sulfur-doped graphene, forming active building blocks, while these building blocks are further shielded by 3D cyclized polyacrylonitrile through the whole electrode; and a novel, conservative flash heat treatment to fabricate Si-based electrodes, which enables a high mass fraction of Si, improved interfacial contact, synergistic SiO2/C coating, and a conductive cellular network for improved electronic conductivity, as well as flexibility for stress compensation. Prof. Yi Cui presented how they rationally designed materials at the nanoscale for nextgeneration batteries. An example includes high-capacity nanostructured Si anodes with stable SEI formation. Prof. Xinping Qiu from Tsinghua University and his group prepared silicon foam with a hollow structure with chemical vapor deposition (CVD). In order to further confine space for SEI growth, they filled pores of hollow structured silicon with PEO electrolyte. With the built-in space, this silicon foam demonstrates remarkable capacity retention and fairly high Coulombic efficiency. Up to now, methods to optimize silicon electrode cycling performance have been extensively described in “half 1629

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ACS Energy Letters

anode in a lithium−sulfur battery: (1) lanthanum nitrate as an electrolyte additive to modify the surface of the lithium anode; (2) LiFSI-LiTFSI binary-salt electrolyte to stabilize the surface of the lithium anode; (3) the porous Al2O3 protective layer on the surface of the metallic lithium anode; and (4) porous carbon paper as an interlayer to protect the lithium anode. The development of Na-ion batteries is moving at a much faster rate, and their use in the market is expected to be in the near future. Very promising results have been reported in recent years showing that the performances of the Na-ion batteries are very competitive for stationary energy storage. Prof. Teóphyllo Rojo from the CIC energiGUNE Center, Spain presented a general overview of the most interesting electrode materials for Na-ion batteries. A great range of possible cathode materials is being screened for Na-ion storage. Energy density over 600 mWh/g has been achieved using layered oxides exhibiting high rate capability, while polyanionic materials such as Na[FexMn1−x]PO4 and Na3V2O2x(PO4)2F3−2x demonstrate good thermal stability and cycle performance at high operation voltage. Regarding the negative electrode, unlike Li-ion batteries, Na+ does not insert into graphite and hard carbon is plagued by slow diffusion and an end-of-charge potential very close to the electroplating of Na0 with risk of dendrites. Two new organic systems, poly-Schiff bases and carbodiimides, have been described. Schiff-base entities show large reversible capacities (∼350 mAh g−1). They have been chemically modified by incorporation of PEO linkers, improving their processing without the use of any binder. The transition metal carbodiimides achieve large capacities (550 mAh g−1) in the first cycles with good cyclability. In addition, batteries based on multivalent cations such as Al3+, Mg2+, and Zn2+ that engage in multiple electron transfer are promising alternatives if they can be employed in conjunction with a metallic anode. Prof. Linda Nazar from the University of Waterloo presented their work on Mg intercalation in some materials such as birnessite, contrasting its behavior in nonaqueous and aqueous electrolytes, and sulfides, a thiospinel Ti2S4 and its layered counterpart TiS2, where highly reversible Mg2+ electrochemical cycling vs a Mg anode is achieved along with capacities as high as 80% of theoretical at a practical rate (C/5) at 60°C. Recent operando X-ray diffraction (XRD) analysis performed during electrochemical Zn2+ (de)intercalation has provided vital probes of structural reversibility over long-term cycling and leads to a better understanding of the complex intercalation behavior in these materials. The visions and requirements of the vehicle manufacturers are important guidance for R&D in both academia and industry. Dr. Peter Lamp from BMW outlined the potential and limits of present material concepts from a car manufacturer point of view. He emphasized that one of the major factors for high market penetration of electric vehicles is the ratio between driving range and price, which requires high energy density and low cost of battery packs. The largest impact on the energy density is the introduction of novel cathode and anode materials for Li-ion cells. For most of the material developments, considerable improvements are needed before possible industrialization of the new generations of batteries for automotive application can be envisaged. Dr. Mark Verbrugge from General Motors overviewed a method to operate lithium−silicon (Li−Si) thick-film electrodes in a manner consistent with traction applications. The operating strategy was based on voltage control of the electrode. He showed that operating Li−Si at both high and low potentials damaged the

Sciences emphasized that the main reason for Li-ion battery safety accidents is the use of flammable organic solution as the electrolyte. Therefore, the research and development of the solid-state battery with a solid ionic conductor as the electrolyte is a very urgent task for solving the safety problem of Li-ion batteries. Prof. Minggao Ouyang from Tsinghua University and his group investigated the multidisciplinary mechanisms of thermal runaway initiation and propagation, created a model database for all aspects of thermal runaway issues, and found a technology platform for designing a safer Li-ion power battery system with less potential of thermal runaway. Prof. Tetsuya Osaka from Waseda University introduced battery assessment technology from analysis of electrochemical impedance spectroscopy (EIS) using an equivalent circuit developed by his group. Instead of using a conventional measurement system of a frequency response analyzer potentiostat, they applied squarecurrent electrochemical impedance spectroscopy (SC-EIS), which is able to detect the low internal resistance of large-scale Li-ion batteries. The SC-EIS technique enabled the operando evolution of battery health of cells and modules. Li-ion and related battery technologies will be important for years to come. However, society needs for energy storage is exceeding that of Li-ion batteries. One alternative to the Li-ion battery is the Li−air (O2) battery; its theoretical specific energy exceeds that of the Li ion, but many hurdles face its realization. The cell operates by reduction of O2 to form Li2O2 at the positive electrode upon discharge and its oxidation upon charge. Conventional electrolytes in Li−O2 batteries promote the formation of a passivating Li2O2 films, which leads to low rate performance. Prof. Peter Bruce from the University of Oxford discussed the implication of moving to a solution- phase growth mechanism for Li2O2 in the Li−O2 battery to achieve high rate and high capacity. New strategies were introduced to avoid passivating Li2O2 films by exploiting the effect of the electrolyte solution. Also, the Li−air battery is plagued by high overpotential (>1.2 V between charge and discharge) and poor cyclability of the cathode due to solid ↔ gas conversion of oxygen. Prof. Ju Li and his group used cobalt oxide confined nanolithia as the cathode in a sealed battery without any gas evolution that can charge/discharge between solid Li2O/Li2O2/ LiO2 with a theoretical capacity of 1341 mAh/g. The cathode shows round-trip overpotential loss of only 0.24 V, a 5-fold improvement compared to that of the gas-evolving Li−air battery. Li−S is another alternate chemistry that could provide much higher energy density than Li-ion batteries but requires a better understanding of the reaction mechanisms with high loading of the active materials and low electrolyte amounts. Dr. Jun Liu from PNNL, the Director of the Battery500 Consortium, presented a careful analysis of the polysulfide deposition mechanisms, which led to new methods to improve the long cycle stability in addition to carbon encapsulation of polysulfides on the cathodes. New electrolytes and additives were used to significantly improve the wetting, ionic conductivity, and electrode integrity against degradation. Passivation of cathodes by polysulfie deposition was identified as a key mechanism for battery failure. In addition, the instability of the metallic lithium anode during lithium electrochemical dissolution/deposition is still a major barrier for practical application of Li−S batteries. Surface modification of the lithium anode is extremely essential, especially for lithium−sulfur cells. Prof. Xueping Gao presented different technological approaches to modify the surface of the lithium 1630

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ACS Energy Letters active material. Dr. Andreas Hintennach from Mercedes-Benz urged the need for a post-lithium-ion technology including a Li−S battery with a silicon-based anode, batteries with nonflammable electrolytes, or solid-state cells, mainly due to limited availability of highly pristine nickel and cobalt and increasing need for recycling, environmental protection, and overall energy efficiency. In summary, this conference covered important progress and perspectives of Li-ion batteries and beyond-Li-ion systems including Li−S, Li−O2, Na-ion batteries, and multivalent cation batteries. Essential challenges and R&D focuses continue to be the energy/power density, durability, safety, and cost of the batteries as the power source of vehicles. We believe that the collaborative efforts of scientists, engineers, and industry leaders will constantly improve the performance of batteries and eventually make an approach to electric vehicles with low cost, long driving range, and low safety risks.

Chun Zhan† Feng Cai‡ Khalil Amine† Jun Lu*,† †

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Chemical Sciences and Engineering Division, Argonne National Laboratory, Argonne, Illinois 60439, United States ‡ China Council for the Promotion of International Trade, Huzhou Committee, Huzhou, Zhejinag Province 313000, China

AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. ORCID

Khalil Amine: 0000-0001-9206-3719 Jun Lu: 0000-0003-0858-8577 Notes

Views expressed in this Energy Focus are those of the authors and not necessarily the views of the ACS. The authors declare no competing financial interest.

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ACKNOWLEDGMENTS The organizers thank Dongyao Qiu, Weijun Chen, Lixing Dong, Gengbao Shi, Fangfang Ding, Quanguan Ding, Yunjuan Yan, Yanlai Xu, and the whole local team for their great effort and support to this conference. C.Z, K.A., and J.L. acknowledge financial support from the U.S. Department of Energy under Contract DE-AC02-06CH11357 from the Vehicle Technologies Office, Department of Energy, Office of Energy Efficiency and Renewable Energy.

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DOI: 10.1021/acsenergylett.7b00407 ACS Energy Lett. 2017, 2, 1628−1631