Accurate estimation of Li/Ni mixing degree of lithium nickel oxide cathode materials

Li/Ni mixing negatively influences the discharge capacity of lithium nickel oxide and high-nickel ternary cathode materials.However,accurately measuring the Li/Ni mixing degree is difficult due to the preferred orientation of labbased XRD measurements using Bragg–Brentano geometry.Here,we find that employing spherical harmonics in Rietveld refinement to eliminate the preferred orientation can significantly decrease the measurement error of the Li/Ni mixing ratio.The Li/Ni mixing ratio obtained from Rietveld refinement with spherical harmonics shows a strong correlation with discharge capacity,which means the electrochemical capacity of lithium nickel oxide and high-nickel ternary cathode can be estimated by the Li/Ni mixing degree.Our findings provide a simple and accurate method to estimate the Li/Ni mixing degree,which is valuable to the structural analysis and screening of the synthesis conditions of lithium nickel oxide and high-nickel ternary cathode materials.

Comparative study of LiNiO_2, LiNi_(0.8)Co_(0. 2)O_2 and LiNi_(0.75)Al_(0.25)O_2 for lithium-ion batteries

The comparative study of LiNi_(0.8)Co_(0.2)O_2 and LiNi_(0.75)A_(0.25)O_2 wascarried out by X-ray diffraction (XRD) and electrochemical methods. The results show that Co and Aldoping suppress the phase transition during charge-discharge. The experiments indi cate thatLiNi_(0.75)Al_(0.25)O_2 has the better cycle-ability and over-charge resistance comparing withLiNi_(0.8)Co_(0.2)O_2. The interfacial behavior was studied by use of electrochemical impedancespectroscopy (EIS). The results show that LiNi_(0.75)Al_(0.25)O_2 has a slightly larger polarizationcharacter than LiNi_(0.8)Co_(0.2)O_2.

Gas Generation Mechanism in Li-Metal Batteries

Gas generation induced by parasitic reactions in lithium-metal batteries(LMB)has been regarded as one of the fundamental barriers to the reversibility of this battery chemistry,which occurs via the complex interplays among electrolytes,cathode,anode,and the decomposition species that travel across the cell.In this work,a novel in situ differential electrochemical mass spectrometry is constructed to differentiate the speciation and source of each gas product generated either during cycling or during storage in the presence of cathode chemistries of varying structure and nickel contents.It unambiguously excludes the trace moisture in electrolyte as the major source of hydrogen and convincingly identifies the layer-structured NCM cathode material as the source of instability that releases active oxygen from the lattice at high voltages when NCM experiences H2→H3 phase transition,which in turn reacts with carbonate solvents,producing both CO_(2)and proton at the cathode side.Such proton in solvated state travels across the cell and becomes the main source for hydrogen generated at the anode side.Mechanisms are proposed to account for these irreversible reactions,and two electrolyte additives based on phosphate structure are adopted to mitigate the gas generation based on the understanding of the above decomposition chemistries.

Synthesis and Electrochemical Property of Calcium Doped LiNi0.8Co0.2O2 Solid Solution

A divalent ion doped LiNi0.8Co0.2O2 solid solution, LiNi0.79Co0.20Ca0.01O2, was synthesized in air at 720℃. The structure and electrochemical property as cathode material of lithium ion batteries were measured by XRD and charge-discharge system. The solid solution showed high capacity and good cycle-ability. The second discharged capacity reached 190 mAh穏-1 at the current density of 100 mA穏-1.

CHARACTERISTICS OF NEW CATHODE MATERIAL FOR LTSOFC INVESTIGATED BY IMPEDANCE SPECTROSCOPY

The characteristics of a new Li-NiO cathode were investigated. The crystal structure of Li-NiO was explored by XRD. Electrochemical behaviors of Li-NiO composite cathode were revealed by impedance spectroscopy from 400℃ to 650℃. The diameter of deformed arc increased with the decrease of temperature. Above the melting point of the eutectic salt in composite electrolyte, the Li-NiO curves are similar with two deformed semicircular arcs at high frequency which partially overlaps each other and corresponds...

Synthesis and Electrochemical Characterization of Gradient Composite LiNi_(1-y)Co_yO_2 Used as Cathode Materials in Lithium-ion Battery

Gradient composites, LiNi1-yCoyO2, are synthesized from coated spherical Ni(OH)2 precursor. These compos-ites could be applied as new cathode materials in lithium-ion batteries because they have low cobalt content (y≤0.2) and exhibit excellent properties during high-rate charge/discharge cycles. The initial discharge capacity of coated composite of LiNi0.95Co0.05O2 is 186 mAh/g, and the decreasing rate of the capacity is 3.2% in 50 cycles at 1 C rate. It has been verified by TEM and EDX experiments that a core-shell structure of the composite particles develops because of the cobalt enrichment near the surfaces, and the formation of the cobalt enrichment layer is sensitive to sintering temperature. High cobalt surface concentration may reduce the undesired reactions and stabilize the struc-ture of the particles.