Thermal Stability and Electrochemical Performance of Graphite Anodes in Li-ion Batteries

PhD i materialteknologiPhD in Materials Science and Engineerin

Effect of strategy and innovation on profitability of knowledge intensive business services in Norway

Master in Business Administration (MBA) - Nord universitet 202

Edge/basal/defect ratios in graphite and their influence on the thermal stability of lithium ion batteries

Raw graphite can be processed industrially in large quanta but for the graphite to be useful in lithium ion batteries (LIB's) certain parameters needs to be optimized. Some key parameters are graphite morphology, active surface area, and particle size. These parameters can to some extent be manipulated by surface coatings, milling processes and heat treatment in various atmospheres. Industrial graphite materials have been investigated for use as anode material in LIB's and compared with commercial graphite. These materials have been exposed to two different milling processes, and some of these materials were further heat treated in nitrogen atmosphere above 2650 °C. Brunauer-Emmett-Teller (BET) theory combined with density functional theory (DFT) has been employed to study the ratio of basal to non-basal plane and to determine the relative amount of defects. Thermal properties have been investigated with differential scanning calorimetry (DSC). High ethylene carbonate (EC) content improved the thermal stability for graphite with high amount of edge/defect surface area, but showed no improvement of graphite with lower amount of edge/defects. High irreversible capacity loss (ICL) combined with low surface area improved the thermal properties. DFT combined with ICL could potentially be used as a tool to predict thermal stability

Electrochemical impedance spectroscopy of a porous graphite electrode used for Li-ion batteries with EC/PC based electrolytes

Electrochemical impedance spectroscopy has been employed to investigate different electrolyte compositions used for lithium-ion batteries. Diffusion coefficients in ethylene carbonate (EC) was estimated to be in order of 10-7-10-11 cm2/s, depending on the state of charge (SOC), and propylene carbonate (PC) based electrolytes has been estimated to be in the order 10-10-10-11 cm2/s. Lithium bis(oxalato) borate (LiBOB) was used as an additive in the PC electrolytes to prevent exfoliation

Electrochemical impedance spectroscopy of a porous graphite electrode used for Li-ion batteries with EC/PC based electrolytes

Electrochemical impedance spectroscopy has been employed to investigate different electrolyte compositions used for lithium-ion batteries. Diffusion coefficients in ethylene carbonate (EC) was estimated to be in order of 10-7-10-11 cm2/s, depending on the state of charge (SOC), and propylene carbonate (PC) based electrolytes has been estimated to be in the order 10-10-10-11 cm2/s. Lithium bis(oxalato) borate (LiBOB) was used as an additive in the PC electrolytes to prevent exfoliation.© The Electrochemical Society. This is the authors' accepted and refereed manuscript to the article

Silicon-carbon composite anodes from industrial battery grade silicon

In this work, silicon/carbon composites for anode electrodes of Li-ion batteries are prepared from Elkem’s Silgrain® line. Gentle ball milling is used to reduce particle size of Silgrain, and the resulting Si powder consists of micrometic Si with some impurities. Silicon/carbon composite with CMC/SBR as a dual binder can achieve more than 1200 cycles with a capacity of 1000 mAh g−1 of Si. This excellent electrochemical performance can be attributed to the use of a buffer as a solvent to control the pH of the electrode slurry, and hence the bonding properties of the binder to the silicon particles. In addition, the use of FEC as an electrolyte additive is greatly contributing to a stabilized cycling by creating a more robust SEI layer. This work clearly demonstrates the potential of industrial battery grade silicon from Elkem.publishedVersio

Temperature effects on performance of graphite anodes in carbonate based electrolytes for lithium ion batteries

The performance of graphite electrodes in various electrolytes containing ethylene carbonate (EC) and mixtures of EC and propylene carbonate (PC) was studied at temperatures between 0 and 40 °C. Included in the study was also the addition of ethyl acetate (EA). Differential scanning calorimetry (DSC) was employed to investigate phase transitions at low temperature (down to −80 °C) and decomposition at elevated temperatures. Capacity loss was compared for graphite electrodes cycled at varying temperatures between 0 and 40 °C for these electrolytes. Based on the results, suitable electrolytes able to work in a wide temperature range could be identified. Addition of EA improved the low temperature properties of the electrolyte and the graphite electrode, but the electrodes failed upon cycling at +40 °C. Addition of PC to a multi-component system, making the total amount of cyclic carbonates 40% (i.e. 20% EC and 20% PC), increased the liquid temperature range of the electrolyte. However, the addition of PC, led to very high initial irreversible capacity loss of the graphite electrode, and reduced the capacity considerably at 0 °C, most likely related to a higher resistance of the solid electrolyte interphase. Thus, mixtures of EC and linear carbonates like dimethyl carbonate (DMC) and ethyl methyl carbonate (EMC) were found to perform best in this temperature range

Anodes for Li‑ion batteries prepared from microcrystalline silicon and enabled by binder’s chemistry and pseudo‑self‑healing

publishedVersio

Silicon-carbon composite anodes from industrial battery grade silicon

In this work, silicon/carbon composites for anode electrodes of Li-ion batteries are prepared from Elkem’s Silgrain® line. Gentle ball milling is used to reduce particle size of Silgrain, and the resulting Si powder consists of micrometic Si with some impurities. Silicon/carbon composite with CMC/SBR as a dual binder can achieve more than 1200 cycles with a capacity of 1000 mAh g−1 of Si. This excellent electrochemical performance can be attributed to the use of a buffer as a solvent to control the pH of the electrode slurry, and hence the bonding properties of the binder to the silicon particles. In addition, the use of FEC as an electrolyte additive is greatly contributing to a stabilized cycling by creating a more robust SEI layer. This work clearly demonstrates the potential of industrial battery grade silicon from Elkem