In fundamental studies of electrode materials for lithium-ion batteries (LIBs) and similar energy storage systems, the main focus is on the capacity, rate capability, and cyclability. The efficiency is usually judged by the coulombic efficiency indicating the electrochemical reversibility. As practical measures, power and energy densities are calculated for discharging, but less attention (if any) is paid to the energy efficiency. Although in the past the energy efficiency was almost close to unity for all electrode materials of LIBs, this factor is critically important for new high-density materials (e.g., based on conversion mechanism) since the energy density can be way below the requirements for the practical development. In fact, a low energy density is due to high overpotentials and is an essential part of the basic research for the material design because it cannot be improved during commercialisation. In large-scale energy storage devices such as batteries in electric vehicles (EVs) or household energy storage systems, the cost of energy consumed to charge the battery is a significant factor and is directly translated into the cost of the energy supplied by the storage device. The present paper clarifies how neglecting the energy efficiency has caused a fraction of research on LIBs to go astray in developing new electrode materials, which are not of practical interest because of huge overpotentials. Particular attention is given to conversion-based electrode materials, which are the common candidates for anode materials of lithium-ion batteries and cathode materials of lithium–sulphur (Li–S) and similar batteries. Furthermore, the impact of nanostructures is considered.

中文翻译：

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能源效率：电池研究中至关重要但却被忽略的因素

在用于锂离子电池（LIB）和类似储能系统的电极材料的基础研究中，主要重点是容量，倍率能力和可循环性。通常通过表明电化学可逆性的库仑效率来判断效率。作为实际措施，计算了用于放电的功率和能量密度，但是对能量效率的关注较少（如果有的话）。尽管在过去，LIB的所有电极材料的能量效率几乎接近统一，但是对于新的高密度材料（例如，（基于转换机制），因为能量密度可能远低于实际开发的要求。实际上，低能量密度是由于过高的电势所致，并且是材料设计基础研究的重要组成部分，因为在商业化过程中无法对其进行改进。在诸如电动车辆（EV）或家用能量存储系统中的电池之类的大规模能量存储设备中，为电池充电所消耗的能量成本是一个重要因素，并直接转化为由存储设备提供的能量成本。本文阐明了忽略能源效率如何导致一部分LIB研究误入了开发新的电极材料的行列，而这种电极材料由于潜力巨大而没有实际意义。特别注意基于转换的电极材料，它们是锂离子电池负极材料以及锂硫（Li-S）电池和类似电池正极材料的常见候选材料。此外，考虑了纳米结构的影响。