Showing papers by "Siqi Shi published in 2022"

Mg2SiO4/Si-Coated Disproportionated SiO Composite Anodes with High Initial Coulombic Efficiency for Lithium Ion Batteries.

Abstract: Silicon monoxide (SiO) is considered as one of the most promising anode material candidates for next-generation high-energy-density lithium ion batteries (LIBs) due to its high specific capacity and relatively lower volume expansion than that of Si. However, a large number of irreversible products are formed during the first charging and discharging process, resulting in a low initial Coulombic efficiency (ICE) of SiO. Herein, we report an economical and convenient method to increase the ICE of SiO without sacrificing its specific capacity by a solid reaction between magnesium silicide (Mg2Si) and micron-sized SiO. The reaction product (named MSO) exhibits a unique core-shell structure with uniformly distributed Mg2SiO4 and Si as the shell and disproportionated SiO as the core. MSO exhibits a superior ICE and a high reversible capacity of 81.7% and 1306.1 mAh g-1, respectively, which can be further increased to 88.7% and 1446.4 mAh g-1 after carbon coating, and improved cyclic stability compared to bare SiO. This work provides a simple yet effective strategy to address the low ICE issue of SiO anode materials to promote the practical application of SiO.

Portraying the ionic transport and stability window of solid electrolytes by incorporating bond valence-Ewald with dynamically determined decomposition methods

Abstract: Designing inorganic solid electrolytes (ISEs) with both excellent electrochemical stability and high ionic conductivity is an important research direction for all-solid-state batteries. However, due to the electronic conduction of hierarchical decomposition products, there is an imbalance between the ionic transport and electrochemical stability window of the ISEs. Here, we propose a computational approach that incorporates bond valence-Ewald energy analysis and dynamically determined decomposition pathway to portray the competing relationship between ionic transport and stable electrochemical window in solid electrolytes. Following this, we explain the high ionic conductivity and wide electrochemical stability window of Li–Si–B–S solid electrolytes, which features shared corner and edge from tetrahedral SiS4/BS4. Our approach is not only applicable to efficiently characterize the previously reported inorganic solid electrolytes but also expected to accelerate the discovery of more systems.

Reclaiming Neglected Compounds as Promising Solid State Electrolytes by Predicting Electrochemical Stability Window with Dynamically Determined Decomposition Pathway

Abstract: The accurate prediction of the electrochemical stability windows (ESWs) enables the rational design of solid state electrolytes (SSEs). Currently, the ESW prediction is based on direct and indirect decomposition analysis methods (DDAM and IDAM). However, DDAM/IDAM can only involve thermodynamically/kinetically favorable decomposition pathway, both resulting in the large deviation between the predicted ESW and the experimental one. Specifically, certain excellent candidate SSEs may be continuously neglected in the high‐throughput screening due to underpredicted ESWs. Herein, a high‐accuracy ESW prediction method is proposed enabling dynamical determination of the appropriate decomposition pathway by analyzing the electronic conductivities of all direct and indirect decomposition products. Following this, a high‐throughput computation is performed on the ESWs of 328 possible fast Li‐ion conductors with low ionic migration energy barriers from the previous research, obtaining good agreement with the available experimental results (Li10GeP2S12 and Li7La3Zr2O12). Furthermore, six previously neglected fluorides exhibiting ESWs over 4 V, oxidation potentials exceeding 6 V, excellent phase stability, and interfacial compatibility with seven typical cathodes are reclaimed as promising SSEs. This work demonstrates a strategy to accelerate the SSE development by improving the accuracy of the ESW prediction and enlarging the database of promising SSEs.

Breaking the Electronic Conductivity Bottleneck of Manganese Oxide Family for High‐Power Fluorinated Graphite Composite Cathode by Ligand‐Field High‐Dimensional Constraining Strategy

Abstract: Primary lithium fluorinated graphite (Li/CFx) batteries with superior energy density are an indispensable energy supply for multiple fields but suffer from sluggish reaction kinetics of the CFx cathode. Designing composite cathodes emerges as a solution to this problem. Despite the optimal composite component for CFx, the manganese oxide family represented by MnO2 is still faced with an intrinsic electronic conductivity bottleneck, which severely limits the power density of the composite cathode. Here, a cation‐induced high‐dimensional constraining strategy from the perspective of ligand‐field stacking structure topological design, which breaks the molecular orbital hybridization of pristine semiconductive oxides to transform them into the high‐conductivity metallic state while competitively maintaining structural stability, is proposed. Through first‐principles phase diagram calculations, mixed‐valent Mn5O8 ( Mn22+Mn34+O8${\rm{Mn}}_2^{2 + }{\rm{Mn}}_3^{4 + }{{\rm{O}}_8}$ ) is explored as an ideal high‐dimensional constraining material with satisfied conductivity and large‐scale production feasibility. Experiments demonstrate that the as‐proposed CFx @ Mn5O8 composite cathode achieves 2.36 times the power density (11399 W kg−1) of pristine CFx and a higher CFx conversion ratio (86%). Such a high‐dimensional field‐constraining strategy is rooted in the established four‐quadrant electronic structure tuning framework, which fundamentally changes the orbital symmetry under the ligand field to overcome the common conductivity challenge of wide transition metal oxide materials.

Software for Evaluating Long-Range Electrostatic Interactions Based on the Ewald Summation and Its Application to Electrochemical Energy Storage Materials.

Abstract: Electrochemical characteristics such as open-circuit voltage and ionic conductivity of electrochemical energy storage materials are easily affected, typically negatively, by mobile ion/vacancy ordering. Ordered phases can be identified based on the lattice gas model and electrostatic energy screening. However, the evaluation of long-range electrostatic energy is not straightforward because of the conditional convergence. The Ewald method decomposes the electrostatic energy into a real space part and a reciprocal space part, achieving a fast convergence in each. Due to its high computational efficiency, Ewald-based techniques are widely used in analyzing characteristics of electrochemical energy storage materials. In this work, we present software not only integrating Ewald techniques for two-dimensional and three-dimensional periodic systems but also combining the Ewald method with the lattice matching algorithm and bond valence. It is aimed to become a useful tool for screening stable structures and interfaces and identifying the ionic transport channels of cation conductors.

Insights into LiMXO4F (M-X = Al-P and Mg-S) as Cathode Coatings for High-Performance Lithium-Ion Batteries.

Abstract: Cathode coatings have received extensive attention due to their ability to delay electrochemical performance degradation in lithium-ion batteries. However, the development of cathode coatings possessing high ionic conductivity and good interfacial stability with cathode materials has proven to be a challenge. Here, we performed first-principles computational studies on the phase stability, thermodynamic stability, and ionic transport properties of LiMXO4F (M-X = Al-P and Mg-S) used as cathode coatings. We find that the candidate coatings are thermodynamically metastable and can be synthesized experimentally. The coating materials possess high oxidative stability, with the materials predicted to decompose above 4.2 V, suggesting that they have good electrochemical stability under a high-voltage cathode. In addition, the candidate coatings exhibit significant chemical stability when in contact with oxide cathodes. Finally, we have studied the Li-ion transport paths and migration barriers of LiMXO4F (M-X = Al-P and Mg-S) and calculated the low migration barriers to be 0.19 and 0.09 eV, respectively. Our findings indicate that LiMXO4F (M-X = Al-P and Mg-S) are promising cathode coatings, among which LiAlPO4F has been experimentally confirmed. The theoretical cathode coating computational methods presented here can be extended to the solid-state battery system.

High ion‐selectivity of garnet solid electrolyte enabling separation of metallic lithium

Abstract: Ionic selectivity is of significant importance in both fundamental science and practical applications. For instance, an ion-selective material allows the passage of a particular kind of ions while blocking the others, which could be used for purification of materials. Herein, the Li-ion-selectivity of a garnet-type solid electrolyte is discussed by comparing the difference of activation energy between different ions migrating in solids. The high ion-selectivity is confirmed by harvesting high-purity metallic lithium (99.98 wt%) from low-lithium-purity sources (80 wt%) at a moderate temperature (190 °C). This gives it huge potential in separating lithium with impurities especially alkali and alkali-earth elements. The cost of metallic lithium production is only 25% of the international lithium price. The proposed electrochemical metallic lithium separating method is advantageous compared with the traditional process in terms of efficiency, safety, and cost.