The proportion of new energy power generation gets higher and higher, due to the depletion of fossil energy resources. However, new energy power is generally unstable, so that it is necessary to use energy storage batteries to balance the power peak and valley. Although lithium-ion batteries have been widely used in various fields, in particular for large-scale energy storage, the low abundance of lithium in the earth crust makes it untenable to meet the ever-intense future demand. Sodium ion batteries, which have similar energy storage mechanism to lithium-ion batteries, have attracted significant attentions due to their abundant raw material resources, low cost, and fairly high energy densities. Layered transition metal oxides are a class of the most promising cathode materials for sodium ion batteries, owing to their high theoretical specific capacities, good conductivity, and fast diffusion kinetics. In this paper, we conduct a comprehensive review of the electrochemical performance, structural characteristics, performance shortcomings and modification technologies about the O3- and P2-type layered transition metal oxide cathode materials. The application potentials of layered materials are summarized and analyzed, which provides a reference for the industry to select the most promising and practical layered cathode material for sodium ion batteries.

It’s critical to quantitatively investigate the thermal characteristics of single overcharged lithium-ion batteries to realize security alert before thermal runaway occurs. In this work, various (LiCoO2 + LiMn2O4)/graphite soft pack cells overcharged under different cut-off voltages, temperatures and C-rates are tested electrochemically to calculate the heat generation rate and distinguish the dominating heat resource. The results show that overcharged cells with higher cut-off voltage, overcharge temperature and the lower overcharge C-rate exhibit higher heat generation and temperature rise rate as well as poorer state of healthy. Among nonexplosive tested cells, the cell overcharged to 4.8 V at 0.1 C rate and 40°C exhibits the highest heat generation and temperature rise rates of 9.17 W·L-1 and 4.60 °C·h-1 during 1 C charging at 25°C. For overcharged cells, lithium plating, increased resistance and gas generation are observed, which are the reason for the accelerated total heat generation rate compared to baseline cells. Comparing with reversible heat, the irreversible heat resulting from diffusion overpotential and the sum of ohmic and charge transfer overpotential is dominating for overcharged cells working under high current. It’s recommended to comprehensively monitor the temperature change of each cell of battery pack.

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Understanding the entropy change (ΔS) characteristics of hard carbon || Na3V2(PO4)3 full cell is crucial for its long cycle life and high safety. This work investigated the thermodynamic data of sodium ion half/full cells based on Na3V2(PO4)3 and hard carbon material. The results show that the trend of ΔS for Na || Na3V2(PO4)3 exhibits great change at 0-10% and 90-100% SOCs (states of charge), and remains constant (≈-14.54 J·mol-1·k-1) in 10-90% SOCs, which is consistent with the characteristics of two-phase reaction. Whereas the ΔS of Na || hard carbon (HC) remains essentially constant (≈8.30 J·mol-1·k-1) in the most Na+ concentration, fluctuating in the range of 3.17-11.71 J·mol-1·k-1. Notably, ΔS shows a negative value (-6.09 J·mol-1·k-1) at x = 0.3 (x in NaxC) and is close to 0 J·mol-1·k-1 at x = 1.0. The HC || Na3V2(PO4)3 full cell entropy change is basically constant (≈-19.56 J·mol-1·k-1) in 10-90% SOCs, and reaches a peak at 60% SOC (-10.75 J·mol-1·k-1), indicating the ΔS of full cell is mainly influenced by Na3V2(PO4)3 electrode. Based on thermodynamic entropy change characteristics, this work aims to provide a reliable reference to the storage, transportation, thermal management, and safety boundary for batteries.