In a rechargeable lithium ion battery lithium ions move from the negative electrode to the positive electrode during discharge, and back when charging.
The cathode is a lithium transition metal oxide, eg manganese or cobalt or a combination of transitional metals. The anode is a graphite-based material, which can intercalate or release lithium.
When discharge begins the lithiated carbon releases a Li+ ion and a free electron.
Electrolyte, that can readily transports ions, contains a lithium salt that is dissolved in an organic solvent. The Li+ ion, which moves towards the electrolyte, replaces another Li + ion from the electrolyte, which moves towards the cathode. At the cathode/electrolyte interface, Li+ ions then become intercalated into the cathode and the associated electron is used by the external device.
When charging takes place, the lithium metal oxide is delithiated and the reverse process ensues.
Equivalent Lithium Content – An estimation of the amount of lithium in a lithium-ion battery based on the Ah or Wh capacity. An approximation is 0.3 grams of lithium metal to produce 1 Ah.
Graphite Anode – A commercial 2600 mAh 18650 Li-ion cell today uses around 10g of graphite anode material.
Lithium Metal Anode Battery
Lithium metal is an ideal anode material for rechargeable batteries due to its extremely high theoretical specific capacity (3860 mA h g-1), low density (0.59 g cm-3) and the lowest negative electrochemical potential (-3.040 V vs. the standard hydrogen electrode).
Failure caused by dendrite growth in high-energy-density, rechargeable batteries with lithium metal anodes has prevented their widespread use. Contrary to conventional wisdom, it seems that preventing dendrite formation in polymer electrolytes depends on inhibiting the formation of subsurface structures in the lithium electrode. [ref: Harry et al]
Lithium Polymer Battery – The battery has a lithium anode that is separated from the cathode by a thin polymer electrolyte.
Lithium Sulphur Battery – A rechargeable battery with a high energy density.
A porous membrane placed between electrodes of opposite polarity, permeable to ionic flow but preventing electric contact of the electrodes.
The considerations that are important and influence the selection of the separator include the following:
- Electronic insulator
- Minimal electrolyte (ionic) resistance
- Mechanical and dimensional stability
- Sufficient physical strength to allow easy handling
- Chemical resistance to degradation by electrolyte, impurities, and electrode reactants and products
- Effective in preventing migration of particles or colloidal or soluble species between the two electrodes
- Readily wetted by electrolyte
- Uniform in thickness and other properties
In most batteries, the separators are either made of nonwoven fabrics or microporous polymeric films. Batteries that operate near ambient temperatures usually use organic materials such as cellulosic papers, polymers, and other fabrics, as well as inorganic materials such as asbestos, glass wool, and SiO2. In alkaline batteries, the separators used are either regenerated cellulose or microporous polymer films. Lithium batteries with organic electrolytes mostly use microporous films.
The type of separator can be divided into the following groups:
- microporous films
- ion exchange membranes
- supported liquid membranes
- solid polymer electrolytes
- solid ion conductors
Silicon Anode – A commercial 2600 mAh 18650 Li-ion cell today uses around 10g of graphite anode material – just 2.6g of structured silicon can replace graphite.
- Pankaj Arora and Zhengming Zhang, “Battery Separators”, Chem. Rev. 2004, 104, 4419-4462
- Wu Xu, Jiulin Wang, Fei Ding, Xilin Chen, Eduard Nasybulin, Yaohui Zhangad and Ji-Guang Zhang, “Lithium metal anodes for rechargeable batteries”, Energy Environ. Sci., 2014, Advance Article
- Katherine J. Harry, Daniel T. Hallinan, Dilworth Y. Parkinson, Alastair A. MacDowell & Nitash P. Balsara, “Detection of subsurface structures underneath dendrites formed on cycled lithium metal electrodes”, Nature Materials 13, 69-73 (2014)