RESUMO
A lithium sulfur composite electrode (SCPV) is prepared by in situ permeation of poly (3,4-dioxyethiophene):poly(styrene sulfonate) (PEDOT:PSS) with a thickness of about 10 nm onto the surface of a SC (sulfur and carbon nanotubes) electrode via a low pressure (3.3 kPa) method. The SCPV electrode exhibits a discharge capacity of 1320.0 mA h g-1, which is higher than that of the SC electrode (1265.8 mA h g-1) at 0.1C; furthermore, it exhibits a discharge capacity of 604.9 mA h g-1, which is almost twice that of the SC electrode (306.8 mA h g-1) at 2C, and it is due to the fact that PEDOT:PSS gel polymers store large amounts of electrolytes and have excellent electronic and ionic conductivities. However, the discharge capacity of a SCPV cathode remains at 91.87% after 200 cycles at 0.5C, which is more than twice that of the SC cathode (44.70%); this superior cycling stability is mainly due to the in situ fixation of PEDOT:PSS inside the SC electrode, which inhibits the shuttle effect and volume change during the cycling process, thus improving the cycling stability.
RESUMO
The Ni-rich LiNi0.8 Co0.10 Mn0.1 O2 (NCM811) cathode coated by combining with multi-walled carbon nanotubes (MWCNTs) and polyimide (PI) produces a PI3-NCM811 cathode, which markedly improves cycling stability and suppresses secondary crystal cracking. The initial discharge capacity of the PI3-NCM811 cathode is 199.6 mAh g-1 between 2.8 and 4.3 V at 0.1 C @ 25 °C, which is slightly lower than that of NCM811 (201.1 mAh g-1 ). The PI3-NCM811 and NCM811 cathodes keep 90.6% and 64.8% of their initial discharge capacity at 1 C between 2.8 and 4.3 V after 500 cycles, respectively. Furthermore, the difference (21.1%) in capacity retention rate between PI3-NCM811 and NCM811 under the condition of 2.8-4.5 V became smaller compared with the difference (25.8%) under the condition of 2.8-4.3 V. This better cyclic stability is mainly attributed to the toughness and elasticity of PI, which inhibits the secondary cracking, maintains the structural integrity of the cathode particles, and protects the particles from electrolyte damage during long-term cycling.
RESUMO
Coating with FePO4 with the size of 20-30 nm on the surface of a LiNi0.8Co0.10Mn0.1O2 (NCM811) cathode produces an LFP3@NCM811 cathode via a sol-gel method, which markedly reduces secondary crystal cracking. A stable particle structure greatly improves the cycling stability of the LFP3@NCM811cathode, which retains 97% of its initial discharge capacity compared to NCM811 (78%) after 100 cycles at 2.7-4.5 V. Furthermore, it retains 86 and 63% of its initial discharge capacity after 400 cycles for LFP3@NCM811 and NCM811, respectively. The initial discharge capacity of the LFP3@NCM811 cathode is 218.8 mAh g-1 at 0.1 C, and the discharge capacity of the LFP3@NCM811 cathode is achieved to be 151.4 mAh g-1 at 5 C, which is 15 mAh g-1 higher than that of the NCM811 cathode. These are due to the reduction of cation mixing for a certain amount of Fe2+/Fe3+ or PO43- doped into the NCM811 surface, and the yolk-shell structure formed by coating with FePO4 helps improve the electronic conductivity and accelerate the Li+ transport. The cycling stability is mainly due to the secondary cleavage inhibition, which maintains the structural integrity of the cathode particles during the long cycle process and protects the inside of the particle from harmful electrolytes.
