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1. Ultrahigh capacity 2D anode materials for lithium/sodium-ion batteries: an entirely planar B ₇ P ₂ monolayer with suitable pore size and distribution

   https://doi.org/10.1039/D0TA02767G  

   Zhu, Changyan ; Lin, Shiru ; Zhang, Min ; Li, Quan ; Su, Zhongmin ; Chen, Zhongfang ( May 2020 , Journal of Materials Chemistry A)

   Lithium-ion batteries (LIBs) are widely used energy storage devices, and sodium-ion batteries (SIBs) are promising alternatives to LIBs because sodium is of high abundance and low toxicity. However, a dominant obstacle for the advancement of LIBs and SIBs is the lack of high capacity anode materials, especially for SIBs. Here, we propose that three characteristics, namely appropriate pore size, suitable pore distribution, and an entirely planar topology, can help achieve ultrahigh capacity 2D anode materials. Under such guidelines, we constructed a B 7 P 2 monolayer, and investigated its potential as a LIB/SIB anode material by means of density functional theory (DFT) computations. Encouragingly, the B 7 P 2 monolayer possesses all the essential properties of a high-capacity LIB/SIB anode: its high stability ensures the experimental feasibility of synthesis, its metallicity does not change upon Li/Na adsorption and desorption, the Li/Na can well diffuse on the surface, and the open-circuit voltage is in a good range. Most importantly, the B 7 P 2 monolayer has a high storage capacity of 3117 mA h g −1 for both LIBs and SIBs, and this capacity value ranks among the highest for 2D SIB anode materials. This study offers us some good cluesmore »to design/discover other anode materials with ultrahigh capacities, and serves us another vivid example that (implicit and hidden) trends/rules in the literature can guide us in the design of functional materials more efficiently.« less
2. Selenium infiltrated hierarchical hollow carbon spheres display rapid kinetics and extended cycling as lithium metal battery (LMB) cathodes

   https://doi.org/10.1039/d1ta04705a  

   Wang, Yixian ; Hao, Hongchang ; Hwang, Sooyeon ; Liu, Pengcheng ; Xu, Yixin ; Boscoboinik, J. Anibal ; Datta, Dibakar ; Mitlin, David ( August 2021 , Journal of Materials Chemistry A)

   Lithium metal–selenium (Li–Se) batteries offer high volumetric energy but are limited in their cycling life and fast charge characteristics. Here a facile approach is demonstrated to synthesize hierarchically porous hollow carbon spheres that host Se (Se@HHCS) and allow for state-of-the-art electrochemical performance in a standard carbonate electrolyte (1 M LiPF 6 in 1 : 1 EC : DEC). The Se@HHCS electrodes display among the most favorable fast charge and cycling behavior reported. For example, they deliver specific capacities of 442 and 357 mA h g −1 after 1500 and 2000 cycles at 5C and 10C, respectively. At 2C, Se@HHCS delivers 558 mA h g −1 after 500 cycles, with cycling coulombic efficiency of 99.9%. Post-mortem microstructural analysis indicates that the structures remain intact during extended cycling. Per GITT analysis, Se@HHCS possesses significantly higher diffusion coefficients in both lithiation and delithiation processes as compared to the baseline. The superior performance of Se@HHCS is directly linked to its macroscopic and nanoscale pore structure: the hollow carbon sphere morphology as well as the remnant open nanoporosity accommodates the 69% volume expansion of the Li to Li 2 Se transformation, with the nanopores also providing a complementary fast ion diffusion path.
3. A dual-role electrolyte additive for simultaneous polysulfide shuttle inhibition and redox mediation in sulfur batteries

   https://doi.org/10.1039/D1TA03425A  

   Rafie, Ayda ; Pai, Rahul ; Kalra, Vibha ( December 2021 , Journal of Materials Chemistry A)

   In Li–S batteries, the insulating nature of sulfur and Li 2 S causes enormous challenges, such as high polarization and low active material utilization. The nucleation of the solid discharge product, Li 2 S, during the discharge cycle, and the activation of Li 2 S in the subsequent charge cycle, cause a potential challenge that needs to be overcome. Moreover, the shuttling of soluble lithium polysulfide intermediate species results in active material loss and early capacity fade. In this study, we have used thiourea as an electrolyte additive and showed that it serves as both a redox mediator to overcome the Li 2 S activation energy barrier and a shuttle inhibitor to mitigate the notorious polysulfide shuttling via the investigation of thiourea redox activity, shuttle current measurements and study of Li 2 S activation. The steady-state shuttle current of the Li–S battery shows a 6-fold drop when 0.02 M thiourea is added to the standard electrolyte. Moreover, by adding thiourea, the charge plateau for the first cycle of the Li 2 S based cathodes shifts from 3.5 V (standard ether electrolyte) to 2.5 V (with 0.2 M thiourea). Using this additive, the capacity of the Li–S battery stabilizes at ∼839more »mA h g −1 after 5 cycles and remains stable over 700 cycles with a low capacity decay rate of 0.025% per cycle, a tremendous improvement compared to the reference battery that retains only ∼350 mA h g −1 after 300 cycles. In the end, to demonstrate the practical and broad applicability of thiourea in overcoming sulfur-battery challenges and in eliminating the need for complex electrode design, we study two additional battery systems – lithium metal-free cells with a graphite anode and Li 2 S cathode, and Li–S cells with simple slurry-based cathodes fabricated via blending commercial carbon black/S and a binder. We believe that this study manifests the advantages of redox active electrolyte additives to overcome several bottlenecks in the Li–S battery field.« less
4. Enhanced performance of Mo ₂ P monolayer as lithium-ion battery anode materials by carbon and nitrogen doping: a first principles study

   https://doi.org/10.1039/D0CP06428A  

   Liu, Xinghui ; Lin, Shiru ; Gao, Jian ; Shi, Hu ; Kim, Seong-Gon ; Chen, Zhongfang ; Lee, Hyoyoung ( February 2021 , Physical Chemistry Chemical Physics)

   By means of density functional theory (DFT) computations, we explored the potential of carbon- and nitrogen-doped Mo 2 P (CMP and NMP) layered materials as the representative of transition metal phosphides (TMPs) for the development of lithium-ion battery (LIB) anode materials, paying special attention to the synergistic effects of the dopants. Both CMP and NMP have exceptional stabilities and excellent electronic conductivity, and a high theoretical maximum storage capacity of ∼ 486 mA h g −1 . Li-ion diffusion barriers on the two-dimensional (2D) CMP and NMP surfaces are extremely low (∼0.036 eV), and it is expected that on these 2D layers Li can diffuse 10 4 times faster than that on MoS 2 and graphene at room temperature, and both monolayers have relatively low average open-circuit voltage (0.38 and 0.4 eV). All these exceptional properties make CMP and NMP monolayers as promising candidates for high-performance LIB anode materials, which also demonstrates that simple doping is an effective strategy to enhance the performance of anode materials in rechargeable batteries.
5. First principles and experimental studies of empty Si ₄₆ as anode materials for Li-ion batteries

   https://doi.org/10.1557/jmr.2016.408  

   Chan, Kwai S. ; Miller, Michael A. ; Liang, Wuwei ; Ellis-Terrell, Carol ; Chan, Candace K. ( December 2016 , Journal of Materials Research)

   The objective of this investigation was to utilize the first-principles molecular dynamics computational approach to investigate the lithiation characteristics of empty silicon clathrates (Si 46 ) for applications as potential anode materials in lithium-ion batteries. The energy of formation, volume expansion, and theoretical capacity were computed for empty silicon clathrates as a function of Li. The theoretical results were compared against experimental data of long-term cyclic tests performed on half-cells using electrodes fabricated from Si 46 prepared using a Hofmann-type elimination–oxidation reaction. The comparison revealed that the theoretically predicted capacity (of 791.6 mAh/g) agreed with experimental data (809 mAh/g) that occurred after insertion of 48 Li atoms. The calculations showed that overlithiation beyond 66 Li atoms can cause large volume expansion with a volume strain as high as 120%, which may correlate to experimental observations of decreasing capacities from the maximum at 1030 mAh/g to 553 mA h/g during long-term cycling tests. The finding suggests that overlithiation beyond 66 Li atoms may have caused damage to the cage structure and led to lower reversible capacities.