In order to confirm reasons that deteriorate cathode performances, Ni-rich Li[Ni0.7Mn0.3]O2 is modified by lithium isopropoxide to artificially provide lithium excess environment by forming Li2O on the surface of active materials. X-ray diffraction patterns indicate that the lithium oxide coating does not affect structural change comparing to the bare material. Scanning electron microscopy and transmission electron microscopy data show the presence of coating layers on the surface of Li[Ni0.7Mn0.3]O2. Electrochemical tests demonstrate that the Li2O-coated Li[Ni0.7Mn0.3]O2 exhibits a greater irreversible capacity with a small capacity because of the presence of insulating layers composed of lithium compounds on the active materials since these layers delay facile Li+ diffusion. Also, the Li2O layer forms byproducts such as Li2CO3, LiOH, and LiF, as are proved by X-ray photoelectron spectroscopy and time-of-flight secondary ion mass spectrometry. The presence of residual lithium tends to bond with hydrocarbons induced from decomposition of electrolytic salt during electrochemical reactions. And the reaction, accelerated by the decomposition of electrolytic salt that produces the byproducts, causes the formation of passive layers on the surface of active material. As a result, the new layers consequently impede diffusion of lithium ions that deteriorate electrochemical properties.

No abstract

Cathode materials are usually active in the range of 2–4.3 V, but the decomposition of the electrolytic salt above 4 V versus Na+/Na is common. Arguably, the greatest concern is the formation of HF after the reaction of the salts with water molecules, which are present as an impurity in the electrolyte. This HF ceaselessly attacks the active materials and gradually causes the failure of the electrode via electric isolation of the active materials. In this study, a bioinspired β‐NaCaPO4 nanolayer is reported on a P2‐type layered Na2/3[Ni1/3Mn2/3]O2 cathode material. The coating layers successfully scavenge HF and H2O, and excellent capacity retention is achieved with the β‐NaCaPO4‐coated Na2/3[Ni1/3Mn2/3]O2 electrode. This retention is possible because a less acidic environment is produced in the Na cells during prolonged cycling. The intrinsic stability of the coating layer also assists in delaying the exothermic decomposition reaction of the desodiated electrodes. Formation and reaction mechanisms are suggested for the coating layers responsible for the excellent electrode performance. The suggested technology is promising for use with cathode materials in rechargeable sodium batteries to mitigate the effects of acidic conditions in Na cells.

In the search for high-capacity anode materials, a facile hydrothermal route has been developed to synthesize phase-pure NiC 2 O 4 ·2H 2 O nanorods, which were crystallized into the orthorhombic structure without using templates. To ensure the electrical conductivity of the nanorods, the produced NiC 2 O 4 ·2H 2 O nanorods were attached to reduced graphene oxide (rGO) sheets via self-assembly layer-by-layer processes that utilize the electrostatic adsorption that occurs in a poly(diallyldimethylammonium chloride) solution. The high electrical conductivity aided by the presence of rGO significantly improved the electrochemical properties: 933 mAh g − 1 for the charge capacity (oxidation), which showed 87.5% efficiency at the first cycle with a retention of approximately 85% for 100 cycles, and 586 mAh g − 1 at 10 C-rates (10 A g − 1 ) for the NiC 2 O 4 ·2H 2 O/rGO electrode. The lithium storage processes were involved in the conversion reaction, which were fairly reversible via a transformation to Ni metal accompanied by the formation of a lithium oxalate compound upon discharge (reduction) and restoration to the original NiC 2 O 4 ·2H 2 O upon charging (oxidation); this was confirmed via X-ray diffraction, transmission electron microscopy, X-ray photoelectron microscopy and time-of-flight secondary ion mass spectroscopy. We believe that the high rate capacity and rechargeability upon cycling are the result of the unique features of the highly crystalline NiC 2 O 4 ·2H 2 O nanorods assisted by conducting rGOs. INTRODUCTIONThe demand for sustainable and green-energy sources is rising because of increasing concerns regarding fast population growth and industrialization worldwide. Lithium-ion batteries have been developed as power sources over several decades and have achieved great commercial success, ranging from mobile to stationary applications. [1][2][3][4] Rechargeable lithium-ion batteries are suitable for the aforementioned applications because of their high energy density and high power properties. 5,6 In commercial batteries, graphite is commonly adopted as the active material for the negative electrodes. Apart from its ability to accommodate Li + ions in its structure and its reversibility, the theoretical capacity of graphite is limited to 372 mAh g − 1 . 7 The predominant intercalation potential of graphite is approximately 0.1 V vs Li/Li + , which results in risks associated with short circuits derived from dendritic growth of Li. In the past, efforts have been made to find high-capacity alternative electrode materials to replace graphite. These new materials can be classified based on their reaction mechanisms: (i) intercalation: Ti-based oxides that store

Recent lithium-ion battery (LIB) technologies power electric vehicles (EVs) to run approximately 220 miles in a single charge, and further effort to increase the energy density of LIBs is being made to run LIB-mounted EVs up to 300 miles in the next few years. Among several important components of LIBs, cathode materials play a significant role in contributing to cost, safety issues, and more importantly energy density. For this concern, Ni-rich cathode materials are indispensable because of their high capacity, reaching over 200 mAh g−1. To commercialize Ni-rich cathode material, tremendous work has been carried out to stabilize the crystal structure and minimize the side reaction with electrolytes, namely, doping, surface modification from nano- to microscale, densification of secondary particles, morphological alternation of primary particles in a secondary particle, and so on. The approaches that have pursued will be discussed in this chapter followed by a perspective.