Abstract
Among many types of batteries, Li-ion and Li-S batteries have been of great interest because of their high energy density, low self-discharge, and non-memory effect, among other aspects. Emerging applications require batteries with higher performance factors, such as capacity and cycling life, which have motivated many research efforts on constructing high-performance anode and cathode materials. Herein, recent research about cathode materials are particularly focused on. Low electron and ion conductivities and poor electrode stability remain great challenges. Three-dimensional (3D) porous nanostructures commonly exhibit unique properties, such as good Li+ ion diffusion, short electron transfer pathway, robust mechanical strength, and sufficient space for volume change accommodation during charge/discharge, which make them promising for high-performance cathodes in batteries. A comprehensive summary about some cutting-edge investigations of Li-ion and Li-S battery cathodes is presented. As demonstrative examples, LiCoO2, LiMn2O4, LiFePO4, V2O5, and LiNi1−x−yCoxMnyO2 in pristine and modified forms with a 3D porous structure for Li-ion batteries are introduced, with a particular focus on their preparation methods. Additionally, S loaded on 3D scaffolds for Li-S batteries is discussed. In addition, the main challenges and potential directions for next generation cathodes have been indicated, which would be beneficial to researchers and engineers developing high-performance electrodes for advanced secondary batteries.
Highlights
Rechargeable batteries are widely used in emergency power backup, electric vehicles, solar power storage, portable equipment, and wearable electronics [1,2]
The synthesized porous LiFePO4/NCNTs composite demonstrates a specific capacity of 159 mAh g−1 at a rate of 0.1 C, a rate performance with a capacity of 72 mAh g−1 at a high rate of 10 C, and a high capacity retention of 96.7% after 500 charge/discharge cycles
The cathode exhibits a good rate performance with a specific capacity of 100 mAh g−1 at 15 C in the potential range of 3.0–4.3 V, which is attributed to the 3D porous frog egg-like structure
Summary
Rechargeable batteries are widely used in emergency power backup, electric vehicles, solar power storage, portable equipment, and wearable electronics [1,2]. For Li-S batteries, as displayed, S8 reacts with Li ions to form high-order lithium polysulfides Li2Sx (4 < x < 8), and lower-order lithium polysulfides Li2Sx (2 < x < 4) are formed as the Li ions insert continuously [14,15,16]. The long-chain lithium polysulfide formed during the discharge process tends to dissolve in the organic electrolytes. When these polysulfides diffuse to the anode through the electrolytes, and react with the lithium anode, the reactions are named as shuttle mechanisms. Dendrites of lithium growing on the surface of the electrode should be removed to ensure battery safety
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