Synthesis And Modification Of LiNi_1-x-yCo_xAl_yO₂ Nickel Rich Cathode Materials

Ni-rich cathode materials Li Ni1-x-y Cox Aly O2, which are generally called NCA, are being considered as very promissing electrodes to replace Li Co O2 due to high reversible specific capacity, excellent cycle performance and low cost. At present, Co-precipitation is one of the most suitable methods for industrial application and uniform spherical particles with homogeneous size can be obtained. In spite of that, there are some shortcomings for the synthesis of NCA materials with excellent electrochemic performance. An elaborate and facial co-precipitation is adopted to synthesiz spherical NCA with good electrochemical performance in this paper. And then, the synergistic mechanism of nickel, cobalt and aluminum metal elements in Li Ni1-x-y Cox Aly O2 system is studied systematacially. After that, the size structureactivity relationship between NCA and carbon based conductive agent is investigated. Finally, NCA electrode is improved by surface modification.Co-precipitation is adopted to synthesiz NCA precursor, and Ni SO4·6H2O, Co SO4·7H2O and Na Al O2 are used as raw materials. At the same time, Na OH and NH3·H2O are used as precipitant and chelating agent. A thermodynamics model of system is established to analyze the feasibility. According to experimental results, it can be concluded that uniform spherical precursor with homogeneous distribution of nickel, cobalt and aluminum metal elements can be obtanied under the followi ng conditions: p H is 11.5, cocentration of NH3·H2O is 0.6 mol/L, feed rate is 0.06 L/min, stirring intensity is 800 rpm and reaction time is above 30 h.NCA electrode with high specific capacity of 214 m Ah/g and good capacity retension of 91.5% after 100 cycles at 0.1 C can be obtained through pre-calcination at 500℃ for 4 h and then calcination at 750℃ for 12 h under the condition of pure oxyen.NCA materials with various ratio of metal elements are synthesized by optimized technological conditions. According to performance tests, it can be known that high capacity is provide by nickel. However, mixing of cation exists in the system of Ni-rich cathode materials. Doping of Co can suppress cation mixing and stabilized layered structure. But too much doping of Co will decrease reversible capacity. Partially doping of Al can improve stabilization of materials. In concluded, Li Ni0.80Co0.15Al0.05O2 is the optimal in the system.Acetylene black, graphite and MCMB are selected as conductive agent based on the prepared NCA to study the size structure-activity relationship among them. From test results, it is indicated that using nano acetylene black as conductive agent can increase contact area due to the distribution of acetylene black on the surface of NCA, which leads to a better electrical conductivity. Finally, carbon co-doping by N and P caoting layer on the surface of NCA is prepared. The electrode conductivity can be effectively improved by coating layer. And as a protective layer, it can suppress the dissolution of the transition metal ions at the particle surface resulting from attack by HF. NCA electrode coated by 1.0 wt.% carbon has the highest capacity retention of 90.7% after 200 cycles at 1 C, which is better than that of pristine NCA.