## 1 Introduction  
Lithium ion batteries (LIBs) are the next generation of power sources for technology such as electric vehicles, mobile phones, and notebook computers, due to its higher energy density, longer cyclic life, faster charge/discharge rates, and better safety. The performance of cathode materials is one of the most important factors that determine the performance of a battery. Therefore, developing a cathode material with high energy density, long cyclic life, and high security is essential [1]. Nickel-rich cathode material Li(Ni\({}_{x}\)M\({}_{1-x}\))O\({}_{2}\) is one of the most applicable cathode materials for advanced LIBs, due to its high energy, power density, and lower cost [2]. Intense research efforts have found that Co and Al co-doping could stabilise the layered structure of LiNiO\({}_{2}\). To date, a Co and Al co-doped NCA has been successfully designed, and it shows excellent thermodynamic stability and electrochemical reactivity with a specific capacity as high as 200 mAh/g. Therefore, NCA shows promise as a candidate for lithium ion batteries, particularly for use in electric vehicles.  
However, some aspects of NCA remain problematic such as poor cycle stability, low electronic conductivity, and the disordered spinel structure in the charged states due to its inherent shortcomings with instability structure at elevated voltages [3; 4; 5]. NCA has been synthesized by various methods including Co-precipitation which is the most common method. To compensate for the loss of lithium at high temperature, excessive lithium is needed in the preparation, however it does not completely evaporate during the high temperature solid phase reaction. Some lithium oxide (Li\({}_{2}\)O) remains on the surface of the cathode materials which can react directly with CO\({}_{2}\) and atmospheric H\({}_{2}\)O to generate Li\({}_{2}\)CO\({}_{3}\) and LiOH [6], as in the reaction shown at Equation (1). In the coating process of battery fabrication, the slurry readily forms a gel and loses its binding ability, which is detrimental to the foil coating. Furthermore, Li\({}_{2}\)CO\({}_{3}\) may react with HF and generate CO\({}_{2}\), resulting in high temperature inflatable and cyclic performance degradation [4]. Additionally, under the highly delithiated state, the reduction of Ni\({}^{4+}\) to Ni\({}^{2+}\) occurred on the NCA surface and led to the release of O\({}_{2}\), and the consequent thermal instability and safety problems.  
\[\ce{LiNi_{0.80}Co_{0.15}Al_{0.05}O_{2}+\frac{1}{2}xO_{2}+\frac{1}{2}xCO_{2}+ \frac{1}{2}xH_{2}O\Rightarrow Li_{1-2x}Ni_{0.80}Co_{0.15}Al_{0.05}O_{2}+\frac{1 }{2}xLi_{2}CO_{3}+xLiOH} \tag{1}\]  
To reduce the residual lithium compound and the pH of NCA, intensive methods have been developed recently:  
1. Controlling the residual lithium compound content by reducing the proportion of lithium salt or by extending the time of the solid phase reaction at high temperature.
2. Washing the cathode materials several times in water, carbonate, organic acids, or organic solvents.
3. Enhancing the capacity and electronic conductivity by coating the electroactive materials; TiO\({}_{2}\), AlF\({}_{3}\), Al\({}_{2}\)O\({}_{3}\), SiO\({}_{2}\), and AlPO\({}_{4}\) have been suggested as suitable coating materials for the layered cathodes [7; 8; 9; 10; 11; 12; 13; 14; 15; 16]. The coating material mainly acts as an isolation layer to prevent side reactions and reduce the pH, which improved thermal stability and cycling stability of the cathode materials.  
In this study, we improved the performance of Ni-rich cathode material NCA using a facile method by modifying LiAlO\({}_{2}\). The results revealed that the residual lithium compound and the pH of NCA was successfully reduced by coating it with LiAlO\({}_{2}\). Furthermore, the SEM images of NCA indicated that the layer was distributed uniformly on the cathode material, which could enhance process ability, safety, and the electrochemical performance of lithium ion batteries.