Materials electrochemistry for high energy density power batteries

On June 30th of 2019, China Association for Science and Technology announced the list of twenty questions that are considered either of guiding importance for frontiers of sciences or playing crucial roles in technological and industrial innovation. Among which the question 4 is materials electrochemistry for high energy density power batteries. This article is an interpretation of this question, including a basic overview of the current technology, industry and market of lithium ion battery for powering electric vehicles, the trends of future development, and where the scientific problems are. Along with the rapid economic development in the last a few decades, the vehicle market in China has grown dramatically in recent years. The total number of vehicles in China is already exceeding 0.2 billion, which makes twenty percent of the total number in the world. And this number keeps increasing at a fast pace since the number of vehicle per capital in China is still much lower than those of developed countries (the average number of vehicles per thousand person at year 2016: China-140, USA-797, Japan-591, Korea-376). The huge number of vehicles in China consume a large amount of fuel oil (about 50% of the total fuel oil consumption of China every year are attributed to vehicles), which is prepared from petroleum, a scarce resource in China. Fossil fuel consumption also causes severe air pollution that threatens people's health and results in global environmental concerns considering the consequences arising from the excessive emission of Greenhouse Gases such as CO2. Development of electric vehicles (EVs) to replace fossil fuel consuming vehicles is a promising solution to tackle the fossil energy exhaustion, global warming, and environment pollution problems, realizing a low-carbon society, and is also an opportunity for China to develop the automobile industry. However, the energy density of the current power batteries used in the EVs is still much lower than that of the fossil energy, which causes the so-called range anxiety in EV drivers, hindering the mass-market penetration of EVs. Therefore, overcoming the range anxiety by developing higher energy density power batteries is a critical technological challenge for innovative revolution of the vehicle market. Usually, driving ranges of at least 500 km are required for EVs to achieve wide customer acceptance. However, the state-of-the-art lithium-ion battery, which has the highest energy density among all mass-produced rechargeable battery systems, barely meets this requirement when battery safety and cycle lifetime are also concerned. Since the energy density of rechargeable batteries is in principle determined by the active anode and cathode materials, the development of new materials chemistry and electrochemistry is the central scientific task for the popularization of EVs. A survey of currently or potentially available active materials is thus helpful in making a technologically sound forecast of battery energy density as well as in setting up EV development roadmap. In this paper, we briefly go through the materials electrochemistry for current and future active materials for lithium ion batteries and lithium metal batteries, thus including both intercalation and conversion reaction mechanisms, and assess the potential of these active materials in the coming decade to achieve energy density as high as 300 Wh/kg or even higher. The scientific questions and technological challenges that need to be addressed to achieve the goal are analyzed and emphasized. We hope this article will help the readers to unravel the complex power battery market, and potentially inspire researchers in the field to solve the materials electrochemistry for high energy density power batteries problem.