Efforts in lithium-ion batteries research have been to improve energy density and power density. Energy density can be improved through the ability to insert/extract more lithium ions from the electrodes. Electrode capacities are compared through three different measures: capacity per unit of mass (known as "specific energy" or "gravimetric capacity"), capacity per unit volume ("volumetric capacity"), and area-normalized specific capacity ("areal capacity"). Separate efforts focus on improving power density (rate of charge/discharge), which is based upon the mass and charge transport, electronic and ionic conductivity, and electron-transfer kinetic; easy transport through shorter distance and greater surface area improve the rate performance of the battery.
Anodes of carbon are traditionally used because of the ability of lithium to intercalate without unacceptable volumetric expansion. High volumetric expansion damages the battery and reduces the amount of lithium available for recharging. The small amount of intercalation into carbonaceous electrodes limits capacity. Carbon based anodes have a gravimetric capacity of 372 mAh/g for LiC6
Silicon has been considered as an anode material because it supports larger amounts of lithium-ion intercalation. The specific capacity of silicon is approximately ten times greater than carbon. The atomic radius of Si is 1.46 angstroms and the atomic radius of Li is 2.05 angstroms. The formation of Li3.75Si causes significant volumetric expansion of the silicon anode..One approach created composite of silicon with less reactive materials to reduce destruction of the electrode, at the cost of lower capacity
Reducing the anode size to the nanoscale offers advantages including improved cycle life and reduced crack propagation and failure. The latter involves reducing the size of silicon particles below the critical flaw size within a conductive binder film. Reducing transport lengths(the distance between the anode and cathode) reduces ohmic losses.
The high surface area available at the nanoscale improves power density due to an increase in the electrochemically active area and a reduction in ionic and electronic transport lengths. However, the increase in surface area to volume ratio at the nanoscale also leads to increased side reactions of the electrode with the electrolyte causing higher self-discharge, reduced charge/discharge cycles and lower calendar life. Some recent work has been focused on developing materials that are electrochemically active within the range where electrolyte decomposition or electrolyte/electrode reactions do not occur.
Nanostructured architectures
For all the advancement of batteries within the past couple decades, a significant majority of battery designs are two –dimensional and rely on layer-by-layer construction. Recent research has taken the nanodes into fully three dimensional structures. Through novel architectures the nanoscalebenefits are maintained while the battery is scaled up. This allows for significant improvements in battery capacity; a significant increase in areal capacity occurs between a 2d thick film electrode and a 3d array electrode.
Silicon has been considered as an anode material because it supports larger amounts of lithium-ion intercalation. The specific capacity of silicon is approximately ten times greater than carbon. The atomic radius of Si is 1.46 angstroms and the atomic radius of Li is 2.05 angstroms. The formation of Li3.75Si causes significant volumetric expansion of the silicon anode..One approach created composite of silicon with less reactive materials to reduce destruction of the electrode, at the cost of lower capacity
The high surface area available at the nanoscale improves power density due to an increase in the electrochemically active area and a reduction in ionic and electronic transport lengths. However, the increase in surface area to volume ratio at the nanoscale also leads to increased side reactions of the electrode with the electrolyte causing higher self-discharge, reduced charge/discharge cycles and lower calendar life. Some recent work has been focused on developing materials that are electrochemically active within the range where electrolyte decomposition or electrolyte/electrode reactions do not occur.
For all the advancement of batteries within the past couple decades, a significant majority of battery designs are two –dimensional and rely on layer-by-layer construction. Recent research has taken the nanodes into fully three dimensional structures. Through novel architectures the nanoscalebenefits are maintained while the battery is scaled up. This allows for significant improvements in battery capacity; a significant increase in areal capacity occurs between a 2d thick film electrode and a 3d array electrode.
EnerG2 introduces nano-structured silicon and carbon into lithium battery cathodes that it claims nearly quadruples electric car range and improve life cycle by 5X.
EnerG2, a Seattle-based company manufacturing advanced nano-structured materials for next-generation energy storage breakthroughs, today announced that it has extended its product lines to further boost lithium-ion battery capacity and power performance. These improvements, designed to harness the benefit of silicon in Lithium-ion batteries, leverage EnerG2’s unique polymer chemistry-based approach and come less than year after launching production of hard carbons tailored for Li-ion anodes.
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