Search

In the pursuit of ever more energy-dense and longer lasting Li-ion batteries, the electrolyte is still an area of intense research. A good choice of electrolyte can make or break the long-term performance of a cell. This paper highlights various advances in electrolyte development and evaluation that have been made in the last several years. Blends of electrolyte additives that give superior capacity retention over several thousand cycles, as well as new formulations of electrolyte solvents to achieve higher charging rates and higher voltage operation are presented. The Advanced Electrolyte Model, a theoretical model for the calculation of electrolyte properties, is presented as an effective way to determine the transport properties of a diverse array of electrolyte systems thus speeding electrolyte development.

Adding esters as co-solvents to Li-ion battery electrolytes can improve low-temperature performance and rate capability of cells. This work uses viscosity and electrolytic conductivity measurements to evaluate electrolytes containing various ester co-solvents, and their suitability for use in high-rate applications is probed. Among the esters studied, methyl acetate (MA) outperforms other esters in its impact on the conductivity and viscosity of the electrolyte. Therefore, viscosity and conductivity were measured as a function of temperature and LiPF6 concentration for electrolytes ethylene carbonate (EC): linear carbonate: MA in the ratio 30:(70-x):x, where linear carbonate = {ethyl methyl carbonate (EMC), dimethyl carbonate (DMC)}, and x = {0, 10, 20, 30}. Adding MA leads to an increase in conductivity and decrease in viscosity over all conditions. Calculations of electrolyte properties from a model based on a statistical-mechanical framework, the Advanced Electrolyte Model (AEM), are compared to all measurements and excellent agreement is found. All electrolytes studied roughly agree with a Stokes' Law model of conductivity. A Walden analysis shows that the ionicity of the electrolyte is not significantly impacted by either MA content or LiPF6 concentration. Li[Ni0.5Mn0.3Co0.2]O2/graphite cells containing MA were cycled at charging rates up to 2C and showed improved cycling performance.

Plating rates and Ni co-deposition were measured for electroless Cu plating baths without and with an added proprietary stabilizer system. The bath has formaldehyde as reducing agent and tartrate as complexing agent. The concentrations of Ni and stabilizer codetermine the plating rate. We investigated this bath over a wide range of compositions, varying the concentrations of stabilizer, Ni, formaldehyde and hydroxyl ions. Stabilized baths without Ni plate very slowly, while with the addition of Ni plating rates are comparable to non-stabilized baths. The amount of Ni in the film is proportional to Ni in the bath for stabilizer-free baths, but becomes dependent on plating rate when the bath is stabilized. Extended absorption fine structure measurements show that the co-deposited Ni is metallic. A quantitative model for time-dependent plating kinetics and Ni incorporation is proposed. The model is based on the inhibition of plating by the adsorption of non-stabilizer and stabilizer species on the plating surface, and it is used to fit plating rates and Ni incorporation for 254 experimental combinations of chemical composition and plating times.