Study on the electronic structure of nickel hydroxide by quantum chemical DV-Xα calculation

Abstract

of β-Ni(OH) 2 were calculated by quantum chemical DV-Xα method. By analyzing the state densities, orbital populations, net charges and electric charge density differences of the selected clusters, it was indicated that β-Ni(OH) 2 was not typical ionic crystal, and the bonds between Ni and O atoms had obvious covalent characteristics. The bonds between H atom and other atoms in the crystal structure were weaker, which ensured that H atoms can easily deintercalate and intercalate into β-Ni(OH) 2 . The structure of β-Ni(OH) 2 was not changed by moderate de-intercalation of H atoms. However, with the excessive de-intercalation of H atoms, the structure of β-Ni(OH) 2 changed and the electrochemical active properties were reduced. nickel hydroxide, electronic structure, quantum chemistry, DV-Xα methodThe nickel-metal hydride (Ni-MH) battery has many characteristics including high energy density, high-rate discharge capability, longer cycle life, no memory effect, no pollution, being easy to fabricate and safe to handle. In the past years, Ni-MH rechargeable battery has been widely used in many fields and is replacing the traditional nickel-cadmium battery [1,2] . It is well known that the capacity of Ni-MH battery depends on the capacity of the positive electrode according to the principle of the rechargeable battery. For nearly ten years, great progress has been made for the hydrogen storage alloy material as a kind of negative electrode material [3] , however, the progress in positive electrode material of Ni-MH battery lags [4,5] .On the other hand, quantum chemical calculation has become a useful tool for battery design since it can be used to calculate most important properties including open circuit voltage, energy density, structure of phases, instability, conductivity of electrode materials without any requirement of experimentally measured input data. Thereby, experimental investigations can be focused on those materials appearing to be most promising [6] . This paper aims to clarify the cycling mechanics of β-nickel hydroxide (β-Ni(OH) 2 ), as a kind of positive electrode material of Ni-MH battery, by analyzing the electronic structures of Ni 7 O 12 H 12 2+ and Ni 7 O 12 H 9 − atom clusters of β-Ni(OH) 2 from quantum chemical DV-Xα calculation. Calculation models and methodChemically prepared β-Ni(OH) 2 consists of a hexagonal sandwich type (Brucite) structure with a plane of nickel atoms in an array of oxygen atoms (OH). Every crystal cell includes one nickel atom, two oxygen atoms and two hydrogen atoms. The distance a 0 between two nickel atoms is 0.312 nm, and the distance c 0 between two layers is 0.4605 nm [7] (Figure 1(a)). By now, of the popular quantum chemical calculation methods, the discrete variational method (DV-Xα) [8]

A Tale of Nickel-Iron Batteries: Its Resurgence in the Age of Modern Batteries

“…When the C-rate was doubled, a high capacity of 145 mAh g −1 was still observed while retaining 90% at the same number of cycles. The in situ sulfurization enabled the formation of a well-conductive sulfide layer that greatly reduced the charge transfer resistance and improved the electrochemical reversibility of the Ni-active materials [166]. Similar observations were reported for composite Ni cathodes with phosphorous-based compounds.…”

“…In some studies, different metals such as calcium and zinc have been doped into the Ni-based electrode, improving the electrode performance. Calcium can reduce the ionization energy of Ni(OH) 2 , which accelerates the electron transfer process and improves the electrode's electrochemical activity [166]. Doping zinc into Ni(OH) 2 , on the other hand, increases charge efficiency and the reversibility of the Ni electrode by preventing the deterioration of β-Ni(OH) 2 to γ-NiOOH [167].…”

Polytypism and Stacking Disorders in Nickel Hydroxide: A First-Principles Study

“…The major contribution to the enthalpy of a solid arises from bond formation within the first coordination shell. 18 Because all the polytypes of nickel hydroxide comprise the same metal hydroxide layer, the bonding within the first coordination shell remains invariant in all of the polytypes. Among the close-packed polytypes ͑1H, 2H 2 , and 3R 2 ͒, the nonbonding HO ¯OH distances are also expected to remain the same in all model structures.…”