Hard-carbon hybrid Li-ion/metal anode enabled by preferred mesoporous uniform lithium growth mechanism

To achieve high energy density in lithium batteries,the construction of lithium-ion/metal hybrid anodes is a promising strategy.In particular,because of the anisotropy of graphite,hybrid anode formed by graphite/Li metal has low transport kinetics and is easy to causes the growth of lithium dendrites and accumulation of dead Li,which seriously affects the cycle life of batteries and even causes safety problems.Here,by comparing graphite with two types of hard carbon,it was found that hybrid anode formed by hard carbon and lithium metal,possessing more disordered mesoporous structure and lithophilic groups,presents better performance.Results indicate that the mesoporous structure provides abundant active site and storage space for dead lithium.With the synergistic effect of this structure and lithophilic functional groups(–COOH),the reversibility of hard carbon/lithium metal hybrid anode is maintained,promoting uniform deposition of lithium metal and alleviating formation of lithium dendrites.The hybrid anode maintains a 99.5%Coulombic efficiency(CE)after 260 cycles at a specific capacity of 500 m Ah/g.This work provides new insights into the hybrid anodes formed by carbon-based materials and lithium metal with high specific energy and fast charging ability.

Engineering homotype heterojunctions in hard carbon to induce stable solid electrolyte interfaces for sodium-ion batteries

Developing effective strategies to improve the initial Coulombic efficiency(ICE)and cycling stability of hard carbon(HC)anodes for sodium-ion batteries is the key to promoting the commercial application of HC.In this paper,homotype heterojunctions are designed on HC to induce the generation of stable solid electrolyte interfaces,which can effectively increase the ICE of HC from 64.7%to 81.1%.The results show that using a simple surface engineering strategy to construct a homotypic amorphous Al_(2)O_(3) layer on the HC could shield the active sites,and further inhibit electrolyte decomposition and side effects occurrence.Particularly,due to the suppression of continuous decomposition of NaPF 6 in ester-based electrolytes,the accumulation of NaF could be reduced,leading to the formation of thinner and denser solid electrolyte interface films and a decrease in the interface resistance.The HC anode can not only improve the ICE but elevate its sodium storage performance based on this homotype heterojunction composed of HC and Al_(2)O_(3).The optimized HC anode exhibits an outstanding reversible capacity of 321.5mAhg^(−1) at 50mAg^(−1).The cycling stability is also improved effectively,and the capacity retention rate is 86.9%after 2000 cycles at 1Ag^(−1) while that of the untreated HC is only 52.6%.More importantly,the improved sodium storage behaviors are explained by electrochemical kinetic analysis.

Enhanced interphasial stability of hard carbon for sodium-ion battery via film-forming electrolyte additive

Although the operating mechanism of sodium-ion battery(SIB)resembles that of lithium-ion battery,common film-forming additive for lithium-ion battery does not play its role in SIB.Therefore,it is essential to tailor new additives for SIB.Hard carbon(HC),as the most used anode material of SIB,has the disadvantage of interphasial instability,especially under the condition of long-term cycling.The incessant accumulation of electrolyte decomposition products leads to a significant increase in interphasial impedance and a sharp decline in discharge capacity.In this work,N-phenyl-bis(trifluoromethanesulfonimide)(PTFSI)was proposed as a novel film-forming electrolyte additive,which effectively enhances the long-term cycling performance for HC anode in SIB.The passivation film generated from the preferential reduction of PTFSI improves the capacity retention of HC/Na half-cell from 0%to 68%after 500 cycles.Profoundly,the enhanced interphasial stability of HC anode results in a 52%increase in capacity retention of HC/Na_(3)V_(2)(PO_(4))_(3)full-cells after 100 cycles.

Boosting the capability of Li_(2)C_(2)O_(4)as cathode pre-lithiation additive for lithium-ion batteries

Li_(2)C_(2)O_(4),with a high theoretical capacity of 525 mAh·g^(−1)and good air stability,is regarded as a more attractive cathode prelithiation additive in contrast to the reported typical inorganic pre-lithiation compounds which are quite air sensitive.However,its obtained capacity is much lower than the theoretical value and its delithiation potential(>4.7 V)is too high to match with the most commercial cathode materials,which greatly impedes its practical application.Herein,we greatly improve the pre-lithiation performance of Li_(2)C_(2)O_(4)as cathode additive with fulfilled capacity at a much-reduced delithiation voltage,enabling its wide applicability for typical commercial cathodes.We increase the capacity of Li_(2)C_(2)O_(4)from 436 to 525 mAh·g^(−1)by reducing its particle size.Through optimizing the types of conductive additives,introducing nano-morphological NiO,MnO2,etc.as catalysts,and innovatively designing a bilayer electrode,the delithiation potential of Li_(2)C_(2)O_(4)is successfully reduced from 4.778 to 4.288 V.We systematically study different particle size,conductive additives,and catalysts on the delithiation behavior of Li_(2)C_(2)O_(4).Finally,it is applied to pre-lithiate the hard carbon anode,and it is found that Li_(2)C_(2)O_(4)could effectively increase the capacity of the full cell from 79.0 to 140.0 mAh·g^(−1)in the first cycle.In conclusion,our study proves that improving the reactivity is an effective strategy to boost the pre-lithiation of Li_(2)C_(2)O_(4).