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In recent years, recycling of numerous spent lithium-ion battery cathode materials has received increasing attention in order to protect the environment as well as to conserve resources, and the recovery of spent LiFePO4 (LFP) by direct regeneration has been widely studied. A considerable body of literature has delved into the failure mechanism of LFP. The mechanism is characterized by an irreversible phase change, which is primarily attributed to the sluggish diffusion of lithium ions (Li+) during cycling. Additionally, the migration of iron (Fe) ions to occupy Li+ sites further impedes Li+ diffusion. Consequently, the electrochemical performance of directly regenerated LFP is diminished by the phenomenon of Li defects. Here, a method of direct regeneration of LFP based on a doping strategy using environmentally friendly and economically efficient natural biomass amino acids has been developed, which inhibits Fe ion migration and improves the diffusion kinetics of Li+ and electrons by constructing a nitrogen-doped carbon coating. The regenerated LFP cathode exhibits excellent cycling stability and rate performance (98.7% capacity retention over 100 cycles at 1C current density and a high capacity retention of 87.9% after 500 cycles at 1C). [ABSTRACT FROM AUTHOR]

Sulfurized polyacrylonitrile (SPAN), featuring uniform dispersion of short-chain sulfur in an organic skeleton, shows great promise in lithium–sulfur (Li–S) batteries due to the inhibited polysulfide dissolution and hence improved electrochemical performance. However, the practical applicability of SPAN is significantly limited by its relatively poor ionic and electronic conductivity, as well as sulfur content (<50%). Herein, triallyl isocyanurate (TI) is incorporated to fabricate SPAN fibers with robust chemical structure and high sulfur loading. The fine-tuned organosulfur cathode (Se0.05S0.95PAN-TI11, 1F) demonstrates increased S&Se content of 54.2% and excellent electrochemical performance in Li/Na–S batteries. As a result, 1F exhibits an ultrahigh composite capacity of 671 mA h g−1 at 0.1C (capacity retention up to 100%) and remarkable rate capability of 405 mA h g−1 at 8C in Li–S batteries. Additionally, 1F shows prolonged cycling ability over 300 cycles at 0.5C when applied in an RT-S battery. Notably, under harsh conditions (S&Se loading of 5.5 mg cm−2 and E/S&Se = 5 μL mg−1), the Li–1F battery displays a brilliant initial areal capacity of 8.0 mA h cm−2 at 0.1C (reversible capacity of 6.3 mA h cm−2) and retains a capacity of 5.3 mA h cm−2 at the 200th cycle (capacity retention of 84%). Consequently, 1F is promising for practical applications in high-performance metal–S batteries. [ABSTRACT FROM AUTHOR]

Inorganic sulfide solid electrolytes with high ionic conductivity and low interfacial resistance attract extensive research attention. Here, we successfully synthesize Li6.7P0.3Ge0.7S5I argyrodite electrolyte with ultrahigh Li-ion conductivity (13.1 mS cm−1 at room temperature) and low activation energy (0.19 eV). All-solid-state lithium batteries based on the prepared electrolyte and pristine LiNi0.8Co0.1Mn0.1O2 cathode show fast capacity degradation due to the side reaction between the active materials and Li6.7P0.3Ge0.7S5I electrolytes. XRD and TEM results confirm the existence of MnO2 and Ni3S2 at the interface between the pristine cathode and solid electrolyte, leading to high resistance and poor electrochemical performances. SEM results indicate that the large volume changes during cycling also contribute to the deteriorating battery performance. A thin layer of the Li2ZrO3 coating layer is then applied onto the surface of cathode materials, which delivers superior capacity properties and cyclability at ambient temperature. The coated electrode also delivers a high area capacity of 5.1 mA h cm−2 with an ultrahigh area loading of 26.8 mg cm−2 at 0.5C at ambient temperature when combined with the Li6.7P0.3Ge0.7S5I electrolytes. Moreover, the assembled battery offers an initial discharge capacity of 107.8 mA h g−1 at 0.1C at −20 °C and maintains a capacity retention of 62% after 200 cycles. [ABSTRACT FROM AUTHOR]

Pyrite (FeS2) is considered an attractive Na-storage anode owing to its abundance, environment friendliness and high theoretical capacity (894 mA h g−1). However, it still remains great challenges to realize an applicable FeS2 electrode with both high reversible capacity and long cycle life. In this study, micron-sized FeS2@C composed of FeS2 nanoparticles uniformly embedded in carbon matrix was investigated as a conversion-type anode for sodium ion batteries by coupling with various electrolytes. It is demonstrated that the electrolyte formulations, i.e., both solvents and Na salts, play vital roles in the Na storage performance of FeS2. The combination of NaPF6 and DME was highly advantageous for constructing robust SEI films with high Na+ conductivity, guaranteeing fast and reversible conversion reactions in the wide electrochemical window of 0.005–3 V (vs. Na/Na+). Owing to the fast charge transfer kinetics and high chemical compatibility between the electrolyte and electrode, the as-prepared FeS2@C could deliver a high reversible capacity of 853 mA h g−1 at 0.2 A g−1 and 459 mA h g−1 at 40 A g−1, a remarkable initial coulombic efficiency of 84.7% and excellent cycling stability with capacity retention of 83.2% over 1000 cycles. These parameters prove the great potential of FeS2@C in fulfiling commercial demands for wide range of energy storage applications. [ABSTRACT FROM AUTHOR]

A type of Na3V2(PO4)3/C (NVP/C) cathode material for sodium ion batteries was synthesized via a facile solid-phase method. Agarose, a natural polysaccharide from seaweed that can form a 3D network structure through hydrogen bonds in polar solvents, was used as a carbon source and a medium to form NVP/C particles as nanograins with a thin layer of carbon coating in a 3D carbon network. As the cathode, the NVP/C material exhibited a reversible capacity of 116 mA h g−1 at 1C, which is very close to its theoretical capacity (117.6 mA h g−1), with a capacity retention of 97.3% after 500 cycles. At 20C, the NVP/C had a capacity of 100 mA h g−1 and still kept a relatively stable capacity of 78 mA h g−1 after being cycled 7000 times. Based on the excellent performance of the obtained cathode material, a sodium ion full cell was assembled with S-doped carbon as the anode, which delivered 110 mA h g−1 of discharge capacity at 200 mA h g−1 (calculated using NVP as the cathode) and displayed an average voltage of around 1.7 V. All of these results imply that the prepared NVP/C has potential for application in sodium ion batteries for large-scale energy storage. [ABSTRACT FROM AUTHOR]

Metallic Sb has been extensively researched as a Na storage anode due to its high capacity and low cost, but it suffers from poor cycling stability stemming from its huge volume change (∼390%) during cycling. Herein, a unique two-dimensional hybrid structure of SbOx nanoplates encapsulated by carbon flakes (SbOx@CF) was fabricated by templating with soluble NaCl. Benefiting from its two-dimensional structure providing rapid Na+ ion uptake and removal and uniform coating endowing a stable buffer layer, the hybrid presents a high reversible capacity (451 mA h g−1) and excellent rate capability (114 mA h g−1 at 4 A g−1), as well as stable cycling (442 mA h g−1 after 100 cycles with 98% capacity retention). This work opens up a facile, controllable, economical and extendable approach to prepare advanced two-dimensional metal oxides for batteries and supercapacitors. [ABSTRACT FROM AUTHOR]