Electrochemical Performance of High-Loading Pure Ni Layered Oxide Electrodes with Functional Conductive Agents

1. Introduction
Pure Ni layered oxides are promising positive electrode candidates for high-energy lithium-ion batteries owing to their large capacity and high operating voltage. Recently, Li-deficient Li_0.975Ni_1.025O₂, as a pure Ni layered oxide, has been reported to show excellent cyclability because the presence of antisite defects in the crystal structure effectively improves the reversibility in the high-voltage region associated with the suppression of Ni ion migration to adjacent tetrahedral sites.¹ To achieve higher energy density of batteries, it is necessary to increase the mass loading of active materials, especially for positive electrodes, while minimizing the content of conductive agents. Therefore, the development of conductive agents that form an efficient electron-conducting path is crucial to fabricate high-loading positive electrodes. In this study, Graphene MesoSponge^® (GMS)² with excellent electronic conductivity and superior chemical stability is selected as conductive agents, and electrochemical properties of high-loading electrodes with the pure Ni layered oxide and GMS are evaluated.
2. Experimental
Li-deficient Li_0.975Ni_1.025O₂ was synthesized by a solid-state reaction.¹ LiOH･H₂O and Ni(OH)₂ were mixed with a mortar and pestle and calcined for 12 h at 650 ^oC under oxygen atmosphere. Electrochemical performance of thick Li_0.975Ni_1.025O₂ composite electrodes (Li_0.975Ni_1.025O₂:conductive agents:poly(vinylidene fluoride) (PVdF) = 96:1:3 in wt%) with different conductive agents, acetylene black (AB), carbon nanotube (CNT) and GMS was evaluated by galvanostatic charge/discharge measurement.
3. Results and discussions
The electronic conductivity of Li_0.975Ni_1.025O₂ composite electrodes was evaluated by impedance measurement. The electronic conductivity increases in the order of AB < CNT < GMS, which indicates that GMS effectively enhances the electronic conductivity of the composite electrodes. Galvanostatic charge/discharge test was also conducted to examine the electrochemical performance of Li_0.975Ni_1.025O₂ composite electrodes. The reversible capacity decreases with continuous cycling for the electrode with AB whereas the capacity degradation is relatively suppressed for the electrodes with CNT and GMS. In addition, the smaller polarization for charge/discharge is observed for the electrode with GMS when compared with AB and CNT. Therefore, GMS is an superior conductive agent that efficiently forms electron-conducting path within the composite electrode even with the minimal addition. From these results, the impact of functional conductive agents on electrochemical performance of high-loading Li_0.975Ni_1.025O₂ electrodes will be discussed in detail.
[1] I. Konuma et al., and N. Yabuuchi, Energy Stor. Mater., 66, 103200 (2024).
[2] H. Nishihara. et al., Adv. Funct. Mater., 26, 6418 (2016).