Junyang Hu (胡俊洋)

The graphite anodes with solvent co-intercalation mechanism exhibit excellent kinetics and cycling stability in sodium-ion batteries. However, the dramatic volume changes caused by solvent participation are challenging for interphasial conformality. Herein, we reveal the intercalation compounds degradation and solid electrolyte interphase (SEI) evolution of graphite at different sodiated state via capacity loss and fluctuation of Coulombic efficiency (CE) induced by calendar aging. The abnormal calendar aging depended on sodiated states is found, which appears as more severe capacity loss and lower CE in partially sodiated graphite anode. The deteriorated performance results from its high-staged intercalated phase transition accompanied by huge volume shrinkage. Under the effect of different intercalation degradation, the growth/destruction of SEI coexists on the partially sodiated graphite, compared to growth …

The continuous solid-electrolyte interphase (SEI) accumulation has been blamed for the rapid capacity loss of carbon anodes in Na and K ethylene carbonate (EC)/diethyl carbonate (DEC) electrolytes, but the understanding of the SEI composition and its formation chemistry remains incomplete. Here, we explain this SEI accumulation as the continuous production of organic species in solution-phase reactions. By comparing the NMR spectra of SEIs and model compounds we synthesized, alkali metal ethyl carbonate (MEC, M = Na or K), long-chain alkali metal ethylene carbonate (LCMEC, M = Na or K), and poly(ethylene oxide) (PEO) oligomers with ethyl carbonate ending groups are identified in Na and K SEIs. These components can be continuously generated in a series of solution-phase nucleophilic reactions triggered by ethoxides. Compared with the Li SEI formation chemistry, the enhancement of the …

Potassium ion batteries using graphite anode and high‐voltage cathodes are considered to be optimizing candidates for large‐scale energy storage. However, the lack of suitable electrolytes significantly hinders the development of high‐voltage potassium ion batteries. Herein, a dilute (0.8 m) fluorinated phosphate electrolyte is proposed, which exhibits extraordinary compatibility with both graphite anode and high‐voltage cathodes. The phosphate solvent, tris(2,2,2‐trifluoroethyl) phosphate (TFP), has weak solvating ability, which not only allows the formation of robust anion‐derived solid electrolyte interphase on graphite anode but also effectively suppresses the corrosion of Al current collector at high voltage. Meanwhile, the high oxidative stability of fluorinated TFP solvent enables stable ultrahigh‐voltage (4.95 V) cycling of a potassium vanadium fluorophosphate (KVPO4F) cathode. Using TFP‐based electrolyte …

The heavy reliance of lithium-ion batteries (LIBs) has caused rising concerns on the sustainability of lithium and transition metal and the ethic issue around mining practice. Developing alternative energy storage technologies beyond lithium has become a prominent slice of global energy research portfolio. The alternative technologies play a vital role in shaping the future landscape of energy storage, from electrified mobility to the efficient utilization of renewable energies and further to large-scale stationary energy storage. Potassium-ion batteries (PIBs) are a promising alternative given its chemical and economic benefits, making a strong competitor to LIBs and sodium-ion batteries for different applications. However, many are unknown regarding potassium storage processes in materials and how it differs from lithium and sodium and understanding of solid–liquid interfacial chemistry is massively insufficient in PIBs …

Graphite is the most commonly used anode material for not only commercialized lithium-ion batteries (LIBs) but also the emerging potassium-ion batteries (PIBs). However, the graphite anode in PIBs using traditional dilute ester-based electrolyte systems shows obvious capacity fading, which is in contrast with the extraordinary cyclic stability in LIBs. More interestingly, the graphite in concentrated electrolytes for PIBs exhibits outstanding cyclic stability. Unfortunately, this significant difference in cycling performance has not raised concern up to now. In this work, by comparing the cyclic stability and graphitization degree of the graphite anode upon cycling, we reveal that the underlying mechanism of the capacity fading of the graphite anode in PIBs is not the larger volume expansion of graphite caused by the intercalation of potassium ions but the continual accumulation of the solid electrolyte interphase (SEI) on the …

Rechargeable potassium (K) metal batteries (PMBs) remain deeply challenged by the lack of suitable electrolytes that are stable against both highly reactive K anodes and 4 V-class cathodes. Despite their good reductive stability with K metal, classic potassium bis(fluorosulfonyl)amide (KFSI)-based ether electrolytes are typically used only in <4.0 V PMBs due to their limited oxidation stability. Herein, a potassium nitrate (KNO3)-containing ether electrolyte, at a moderate KFSI concentration (2.3 M) rather than a high concentration (normally, >3 M), is reported for the first time to be used in 4 V-class PMBs. A stable N/F-rich solid electrolyte interphase (SEI) is formed, enabling dense and uniform K deposition, especially under high current density. Remarkably, the PMBs with Prussian blue cathode exhibits an unprecedented cycle life (1000 cycles, 122 days). This work provides new perspectives of electrolyte design for …

Sodium and potassium metal batteries are being developed and studied enthusiastically by researchers, but the electrochemical deposition mechanism of sodium and potassium are still elusive and considered as analogs of the lithium version. In this study, it is found that the deposition of sodium and potassium are different from lithium. During deposition, cations get electrons and turn into metal deposited beneath the solid electrolyte interphase (SEI), and consequently the SEI is subject to the pressure from the metal around the deposition sites. Under the pressure, the SEI of lithium is strong enough to keep its integrity, which leads to the root growth of deposits. The lithium deposits are whiskers with the diameter of submicrometer and can be blocked by separators with the pores of dozens of nanometers. By contrast, the SEIs of sodium and potassium are weak and break into fragments under the pressure, and the …

As emerging energy storage systems, potassium-ion batteries (PIBs) are suitable for grid-scale energy storage application due to the abundant potassium resources and low cost. It is crucial to achieve fast-charging PIBs. However, as the most promising anode candidate, graphite still faces setbacks in achieving fast charging due to poor kinetic issue. Herein, modified graphite (MG) is synthesized to realize the fast potassium ion storage. Benefiting from the enlarged graphitic space combined with unique porous microstructure, MG exhibits outstanding electrochemical performance. The optimized MG anode delivers a specific capacity of 115 mAh g−1 at 4 A g−1 and excellent cycling stability of 1500 cycles at 1 A g−1. Moreover, the full cell assembled with MG anode and Prussian Blue (PB) cathode exhibits a capacity retention of 75% after 20000 cycles at the current density of 1 A g−1. The excellent electrochemical …

Potassium-ion batteries (PIBs) as an alternative to lithium-ion batteries have attracted much interest and develop rapidly. Among the cathode materials, polyanionic compounds present both high discharge voltage and considerable capacity owing to their unique skeleton and strong inductive effect from anion groups. In this work, a K0.5VOPO4·1.5H2O/graphene oxide composite as a polyanionic cathode material for PIBs was synthesized by a simple chemical precipitation method. The composite delivers a high capacity of 118 mA h g–1 with a competitive energy density of 402 W h kg–1. With GO modification, the composite also shows superior cycle and rate performance. The simple synthesis process and excellent performance enable it to have commercial potential in the future.

Nowadays, alkali metal-oxygen batteries such as Li-, Na-, and K-O2 batteries have been investigated extensively because of their ultrahigh energy density. However, the oxygen crossover of oxygen batteries and the intrinsic drawbacks of the metal anodes (i.e., large volume changes and dendrite issues) have still been unsolved key problems. Here, we demonstrate a novel design of the K-ion oxygen battery using a graphite intercalation composite as the anode in a highly concentrated ether-based electrolyte. Instead of the metal K anode, the potassium graphite intercalation compound as the anode is depotassiated/potassiated in a binary form below 0.3 V (vs. K+/K); correspondingly, the discharged product KO2 is formed/decomposed at the carbon nanotube cathode, and an all-carbon full cell exhibits impressive cycling stability with a working voltage of 2.0 V. Furthermore, the utilization of graphite intercalation …