Stress-Regulation Design of Lithium Alloy Electrode toward Stable Battery Cycling

Metallic tin(Sn)foil is a promising candidate anode for lithium-ion batteries(LIBs)due to its metallurgical processability and high capacity.However,it suffers low initial Coulombic efficiency and inferior cycling stability due to its uneven alloying/dealloying reactions,large volume change and stress,and fast electrode structural degradation.Herein,we report an undulating LiSn electrode fabricated by a scalable two-step procedure involving mechanical lithography and chemical prelithiation of Sn foil.With the combination of experimental measurements and chemo-mechanical simulations,it was revealed the obtained undulating LiSn/Sn electrode could ensure better mechanical stability due to the pre-swelling state from Sn to Li x Sn and undulating structure of lithography in comparison with plane Sn,homogenize the electrochemical alloying/dealloying reactions due to the activated surface materials,and compensate Li loss during cycling due to the introduction of excess Li from Li_(x)Sn,thus enabling enhanced electrochemical performance.Symmetric cells consisting of undulating LiSn/Sn electrode with an active thickness of∼5 um displayed stable cycling over 1000 h at 1 mA cm^(-2) and 1 mAh cm^(-2) with a low average overpotential of<15 mV.When paired with commercial LiNi_(0.6)Co_(0.2)Mn_(0.2)O_(2)(NCM622)cathode with high mass loading of 15.8 mg cm^(-2),the full cell demonstrated a high capacity of 2.4 mAh cm^(-2) and outstanding cycling stability with 84.9% capacity retention at 0.5 C after 100 cycles.This work presents an advanced LiSn electrode with stress-regulation design toward high-performance LIBs,and sheds light on the rational electrode design and processing of other high-capacity lithium alloy anodes.

Circumventing chemo-mechanical failure of Sn foil battery anode by grain refinement and elaborate porosity design

Tin (Sn) metal foil is a promising anode for next-generation high-energy–density lithium-ion batteries (LIBs) due to its high capacity and easy processibility. However, the pristine Sn foil anode suffers nonuniform alloying/dealloying reaction with lithium (Li) and huge volume variation, leading to electrode pulverization and inferior electrochemical performance. Herein, we proposed that reduced grain size and elaborate porosity design of Sn foil can circumvent the nonuniform alloy reaction and buffer the volume change during the lithiation/delithiation cycling. Experimentally, we designed a three-dimensional interconnected porous Sn (3DIP-Sn) foil by a facile chemical alloying/dealloying approach, which showed improved electrochemical performance. The enhanced structure stability of the as-fabricated 3DIP-Sn foil was verified by chemo-mechanical simulations and experimental investigation. As expected, the 3DIP-Sn foil anode revealed a long cycle lifespan of 4400 h at 0.5 mA cm^(−2) and 1 mAh cm^(−2) in Sn||Li half cells. A 3DIP-Sn||LiFePO_(4) full cell with LiFePO_(4) loading of 7.1 mg cm^(−2) exhibited stable cycling for 500 cycles with 80% capacity retention at 70 mA g^(−1). Pairing with high-loading commercial LiNi0.6Co0.2Mn0.2O_(2) (NCM622, 18.4 mg cm^(−2)) cathode, a 3DIP-Sn||NCM622 full cell delivered a high reversible capacity of 3.2 mAh cm^(−2). These results demonstrated the important role of regulating the uniform alloying/dealloying reaction and circumventing the localized strain/stress in improving the electrochemical performance of Sn foil anodes for advanced LIBs.

Cobalt doping boosted electrocatalytic activity of CaMn3O6 for hydrogen evolution reaction

The development of earth-abundant-metal-based electrocatalysts with high efficiency and long-term stability for hydrogen evolution reaction(HER)is crucial for the clean and renewable energy application.Herein,we report a molten-salt method to synthesize Co-doped CaMn_(3)O_(6)(CMO)nanowires(NWs)as effective electrocatalyst for HER.The as-obtained CaMn_(3-x)Co_(x)O_(6)(CMCO)exhibits a small onset overpotential of 70 mV,a required overpotential of 140 mV at a current density of 10 mA·cm^(-2),a Tafel slope of 39 mV·dec^(-1)in 0.1 M HClO_(4),and a satisfying long-term stability.Experimental characterizations combined with density functional theory(DFT)calculations demonstrate that the obtained HER performance can be attributed to the Co-doping which altered CMO’s surface electronic structures and properties.Considering the simplicity of synthesis route and the abundance of the pertinent elements,the synthesized CMCO shows a promising prospect as a candidate for the development of earth-abundant,metal-based,and cost-effective electrocatalyst with superior HER activity.Our results also establish a strategy of rational design and construction of novel electrocatalyst toward HER by tailoring band structures of transition metal oxides(TMOs).