Aqueous Li-ion Battery:a potential system for stationary power application

The stability and reliability of electricity grids requires a continuous balance between energy supply and demand. Renewable generation, such as solar and wind, is intermittent, which causes sudden and unanticipated changes to power output and contributes to electricity grid instability. For example, the intermittency associated with photo-voltaic(PV) generation, wind turbines is prohibiting the rapid adoption of utility-scale i ntegration with the grid systems.
The lithium-ion battery using two intercalated compounds (carbon anode and LiCo02
cathode) in an organic solution electrolyte was commercialized by Sony in 1990 and is now widely used for cellular phones, notebook-size personal computers, video and digital cameras, and other electronics owing to its long cycling capability and high energy density.
However, despite the remarkable performance of these organic based systems, they suffer from the use of highly toxic and flammable solvents, which can cause safety hazards if usedimproperly, such as overcharging or short-circuiting, specially use for large-scale battery.
Switching to a water-based electrolyte would be cheaper and safer and is feasible using specially designed electrodes, but water-based batteries have not been as reliable as their organic counterparts. Until now, the best aqueous cells to be developed lose around 50 per cent of their storage capacity after being recharged 100 times.

We analyzed the stability of electrode materials in aqueous electrolytes extensively. We found that, in the presence of oxygen, the discharged state of lithium-ion intercalated compounds(LIC) of all negative electrode materials suitable for aqueous lithium-ion batteries reacts with water and O2, with no dependence on the pH value of the electrolyte, which is mainly responsible for the capacity fading of aqueous lithium-ion batteries during charge/discharge cycling. By eliminating the O2(using a sealed cell), adjusting the pH values of the electrolyte, and using carbon-coated electrode materials,a LiTiz(PO:):/LiFePOa aqueous LIB in a LiSO: aqueous electrolyte can cycle over 1000
cycles with a capacity retention above 90%.

We also use a activated carbon as negative electrode to develop a new concept hybridelectrochemical supercapacitor in which a Li-ion intercalated compound was used as a positive electrode in combination with an activated carbon negative electrode in a Li2SO; aqueous electrolyte. The negative electrode stores charge through a reversible nonfaradaic reaction of Li-ion on the surface of an activated carbon. The positive electrode utilizes areversible faradic reaction of Li-ion insertion/extraction in the lithium-ion intercalated compounds. By optimizing the cell composition and charge/discharge condition, the hybrid cell shows the exciting results. For example, the hybrid cell consisting of a spinelLiMn2O; positive and an AC negative electrode shows excellent reversibility with a sloping voltage profile from 0.8 to 1.8 V at an average voltage near 1.3 V, and delivers an estimated specific energy of ca.35 Wh/kg based on the total weight of the active electrode materials.
Even the energy density of these aqueous lithium batteries cannot compete with that of its organic counterpart for portable electronics in terms of its high safety, long cycling life, high power, low cost, low toxicity, which make it the most suitable for short-distance city-bus and stationary power sources to store energy from sustainable sources, such as the wind and solar power.


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