LIB Anodes

Graphite Pros

372mAh/g, low volume expansion (~10%), low electrochemical potential (0.17 close to Li) maximises cell voltage, stable SEI, good conductivity (10^4S/cm), cheap, abundant, long cycle life 500-1000

Graphite cons

slow Li+ diffusion (limits charging speed), Li plating at high T or current, ~10% capacity loss to SEI, exfoliation with some electrolytes, modest capacity

Graphite intercalation process

1 Li per 6 C, Li occupies every third C6 ring, will fill every 4th gallery then every 3rd, 2nd and then all galleries, each stage gives distinct voltage plateau

Natural graphite

single crystals, higher capacity

Artificial graphite

from petroleum coke, better life cycle, lower capacity

Li metal pros

low potential (maximum cell voltage), v high capacity 3862mAh/g

Li metal cons

uneven Li deposition causes dendrites and expansion, capacity loss from detached Li, both increase SEI formation, Li and electrolyte lost in corrosion reaction

Si anodes

alloying mechanism, 1Si to 4Li, 3579mAh/g, low potential (0.4); BUT: 300% expansion causing cracking and cell failure, low ionic conductivity

Spinel Li4Ti5O12 as an anode

Li inserted via two phase reaction to form rocksalt Li7Ti5O12 with very little strain, <0.2% volume change, >10,000 cycles

Spinel Li4Ti5O12 pros

low expansion, no SEI formation (1.55V is within electrolyte stability window), low V prevents Li plating = safer, fast Li diffusion along spinel channels = faster charging

Spinel Li4Ti5O12 cons

low voltage = low energy density, slow Li diffusion and low e conductivity, moderate capacity 175mAh/g

Conversion materials

break and reform chemical bonds during cycle, >800mAh/g due to multiple e per atom

State of the art

dope graphite with Si NPs to increase capacity, but have to manage Si expansion; coat graphite with oxides or phosphates to improve charging rate by reducing Li plating; Artificial graphite optimisation: mixture of small and big particles for good packing and better rate capability; Prelithiation: compensate for 1st cycle loss, add Li powder, increases energy density by 5-15%

Graphene

double graphite capacity as Li adsorbs onto both sides (and on edges), restacking hard to prevent, large SA = large SEI losses, v expensive

Hard Carbon

disordered carbon with no long range crystallinity, intercalation, pore filling and adsorption; good for low T use and high rate capability