Haoran Jiang

Boron phosphide monolayer as a potential anode material for alkali metal-based batteries

In this work, we adopt a first-principles study to evaluate the potential of boron phosphide (BP) monolayer as an anode material for alkali metal-based (e.g., Li, Na and K) batteries. It is found that the BP monolayer shows negative adsorption energies of −0.202, −0.160 and −0.681 eV, respectively, for Li, Na and K. During loading, when any of the three alkali metal atoms reaches a critical position (∼6 A), the adsorption energy increases dramatically with no energy barrier. It is also shown that after adsorbing Li, Na or K, the semiconducting BP monolayer is transformed to a metallic state, becoming an electrical conductor. More importantly, the alkali metal atoms show high diffusivities on the BP monolayer, with low energy barriers of 0.364, 0.217 and 0.155 eV for Li, Na and K, respectively. Finally, the BP monolayer has high theoretical specific capacities of 1283 and 570 mA h g−1 for Li and K storages, which are among the highest values of the anode materials reported in the literature, and multiple times higher than that of graphite anode materials in use. The above-mentioned results suggest that the BP monolayer is a promising anode material not only for Li-ion and K-ion batteries, but also for other lithium-based and potassium-based batteries.

A Lithium/Polysulfide Battery with Dual-Working Mode Enabled by Liquid Fuel and Acrylate-Based Gel Polymer Electrolyte

The low density associated with low sulfur areal loading in the solid-state sulfur cathode of current Li-S batteries is an issue hindering the development of this type of battery. Polysulfide catholyte as a recyclable liquid fuel was proven to enhance both the energy density and power density of the battery. However, a critical barrier with this lithium (Li)/polysulfide battery is that the shuttle effect, which is the crossover of polysulfides and side deposition on the Li anode, becomes much more severe than that in conventional Li-S batteries with a solid-state sulfur cathode. In this work, we successfully applied an acrylate-based gel polymer electrolyte (GPE) to the Li/polysulfide system. The GPE layer can effectively block the detrimental diffusion of polysulfides and protect the Li metal from the side passivation reaction. Cathode-static batteries utilizing 2 M catholyte (areal sulfur loading of 6.4 mg cm-2) present superior cycling stability (727.4 mAh g-1 after 500 cycles at 0.2 C) and high rate capability (814 mAh g-1 at 2 C) and power density (∼10 mW cm-2), which also possess replaceable and encapsulated merits for mobile devices. In the cathode-flow mode, the Li/polysulfide system with catholyte supplied from an external tank demonstrates further improved power density (∼69 mW cm-2) and stable cycling performance. This novel and simple Li/polysulfide system represents a significant advancement of high energy density sulfur-based batteries for future power sources.

Borophene and defective borophene as potential anchoring materials for lithium–sulfur batteries: a first-principles study

Lacking effective anchoring materials to suppress the severe shuttle effect is a longstanding issue hindering the development of lithium–sulfur (Li–S) batteries. In this work, a first-principles study is carried out to investigate the potential of borophene and defective borophene, which have high ionic conductivity and adsorbent ability, as anchoring materials for Li–S batteries. Borophene is found to exhibit ultra-high adsorption energies towards lithium polysulfides, but the material facilitates the decomposition of Li–S clusters, leading to an undesirable sulfur loss during battery cycling. For this reason, borophene is not an ideal anchoring material for Li–S batteries. On the contrary, defective borophene is found to show moderate adsorption energies ranging from 1 to 3 eV, which not only effectively anchors lithium polysulfides to suppress the shuttle effect, but also keeps their cyclic structures undecomposed. In addition, defective borophene exhibits a metallic characteristic during the whole reaction process, ensuring the lithium polysulfides be easily charged back and not accumulate on the anchoring materials. Given these advantages, it is expected that defective borophene is a promising anchoring material, leading to a suppressed shuttle effect and enhanced capacity retention for Li–S batteries.

Highly efficient and ultra-stable boron-doped graphite felt electrodes for vanadium redox flow batteries

Developing high-performance electrodes with high operating current densities and long-term cycling stability is crucial to the widespread application of vanadium redox flow batteries (VRFBs). In this work, boron-doped graphite felt electrodes are designed, fabricated and tested for VRFBs. The first-principles study first demonstrates that the boron-doped carbon surface possesses highly active and stabilized reaction sites. Based on this finding, boron-doped graphite felt electrodes are fabricated for VRFBs. Testing results show that the batteries with boron-doped graphite felt electrodes achieve energy efficiencies of 87.40% and 82.52% at the current densities of 160 and 240 mA cm−2, which are 15.63% and 19.50% higher than those with the original electrodes. In addition, the batteries can also be operated at high current densities of 320 and 400 mA cm−2 with energy efficiencies of 77.97% and 73.63%, which are among the highest performances in the open literature. More excitingly, the VRFBs with the boron-doped graphite felt electrodes exhibit excellent stability during long-term cycling tests. The batteries can be stably cycled for more than 2000 cycles at 240 mA cm−2 with ultra-low capacity and efficiency decay rates of only 0.028% and 0.0002% per cycle. In addition, after refreshing the electrolytes, the performances of the batteries are nearly recovered regardless of the inevitable decay of the membrane. All these results suggest that highly efficient and ultra-stable boron-doped graphite felts are promising electrodes for VRFBs.