Using First‐Principles Calculations for the Advancement of Materials for Rechargeable Batteries

Rechargeable batteries have been regarded as leading candidates for energy storage systems to satisfy soaring energy demands and ensure efficient energy use, and intensive efforts have thus been focused on enhancing their energy densities and power capabilities. First‐principles calculations based on quantum mechanics have played an important role in obtaining a fundamental understanding of battery materials, thus providing insights for material design. In this feature article, the theoretical approaches used to determine key battery properties, such as the voltage, phase stability, and ion‐diffusion kinetics, are reviewed. Moreover, the recent contribution of first‐principles calculations to the interpretation of complicated experimental characterization measurements on battery materials, such as those obtained using X‐ray absorption spectroscopy, electron energy‐loss spectroscopy, nuclear magnetic resonance spectroscopy, and transmission electron microscopy, are introduced. Finally, perspectives are provided on the research direction of first‐principles calculations for the development of advanced batteries, including the further development of theories that can accurately describe the dissolved species, amorphous phases, and surface reactions that are integral to the operation of future battery systems beyond Li‐ion batteries.     

A Family of High‐Performance Cathode Materials for Na‐ion Batteries,Na3(VO1−xPO4)2 F1+2x (0 ≤ x ≤ 1): Combined First‐Principles and Experimental Study

Room‐temperature Na‐ion batteries (NIBs) have recently attracted attention as potential alternatives to current Li‐ion batteries (LIBs). The natural abundance of sodium and the similarity between the electrochemical properties of NIBs and LIBs make NIBs well suited for applications requiring low cost and long‐term reliability. Here, the first successful synthesis of a series of Na₃(VO_1?x PO₄)₂F_1+2x (0 ≤ x ≤ 1) compounds as a new family of high‐performance cathode materials for NIBs is reported. The Na₃(VO_1?x PO₄)₂F_1+2x series can function as high‐performance cathodes for NIBs with high energy density and good cycle life, although the redox mechanism varies depending on the composition. The combined first‐principles calculations and experimental analysis reveal the detailed structural and electrochemical mechanisms of the various compositions in solid solutions of Na₃(VOPO₄)₂F and Na₃V₂(PO₄)₂F₃. The comparative data for the Na _y (VO_1?x PO₄)₂F_1+2x electrodes show a clear relationship among V³⁺/V⁴⁺/V⁵⁺ redox reactions, Na⁺?Na⁺ interactions, and Na⁺ intercalation mechanisms in NIBs. The new family of high‐energy cathode materials reported here is expected to spur the development of low‐cost, high‐performance NIBs.     

Three‐Dimensional Porous Copper–Tin Alloy Electrodes for Rechargeable Lithium Batteries

Three‐dimensional (3D) foam structure of a Cu₆Sn₅ alloy was fabricated via an electrochemical deposition process. The walls of the foam structure are highly porous and consist of numerous small grains. When used as a negative electrode for a rechargeable lithium battery, the Cu₆Sn₅ samples delivered a reversible capacity of about 400 mA h g^–1 up to 30 cycles. Further, these materials exhibit superior rate capability, attributed primarily to the unique porous structure and the large surface area for fast mass transport and rapid surface reactions. For instance, at a current drain of 10 mA cm^–2 (20C rate), the obtainable capacity (220 mA h g^–1) was more than 50 % of the capacity at 0.5 mA cm^–2 (1C rate).     

Strain Accommodation during Phase Transformations in Olivine‐Based Cathodes as a Materials Selection Criterion for High‐Power Rechargeable Batteries

High energy lithium‐ion batteries have improved performance in a wide variety of mobile electronic devices. A new goal in portable power is the achievement of safe and durable high‐power batteries for applications such as power tools and electric vehicles. Towards this end, olivine‐based positive electrodes are amongst the most important and technologically enabling materials. While certain lithium metal phosphate olivines have been shown to be promising, not all olivines demonstrate beneficial properties. The mechanisms allowing high power in these compounds have been extensively debated. Here we show that certain high rate capability olivines are distinguished by having extended lithium nonstoichiometry (up to ca. 20 %), with which is correlated a reduced lattice misfit as the material undergoes an electrochemically driven, reversible, first‐order phase transformation. The rate capability in several other intercalation oxides can also be correlated with lattice strain, and suggests that nanomechanics plays an important and previously unrecognized role in determining battery performance.     

Na2FeP2O7 as a Promising Iron‐Based Pyrophosphate Cathode for Sodium Rechargeable Batteries: A Combined Experimental and Theoretical Study

Considering the promising electrochemical performance of the recently reported pyrophosphate family in lithium ion batteries as well as the increasing importance of sodium ion batteries (SIBs) for emerging large‐scale applications, here, the crystal structure, electrochemical properties, and thermal stability of Na₂FeP₂O₇, the first example ever reported in the pyrophosphate family for SIBs, are investigated. Na₂FeP₂O₇ maintains well‐defined channel structures (triclinic framework under the P1 space group) and exhibits a reversible capacity of ≈90 mAh g^?1 with good cycling performance. Both quasi‐equilibrium measurements and first‐principles calculations consistently indicate that Na₂FeP₂O₇ undergoes two kinds of reactions over the entire voltage range of 2.0–4.5 V (vs Na/Na⁺): a single‐phase reaction around 2.5 V and a series of two‐phase reactions in the voltage range of 3.0–3.25 V. Na₂FeP₂O₇ shows excellent thermal stability up to 500 °C, even in the partially desodiated state (NaFeP₂O₇), which suggests its safe character, a property that is very critical for large‐scale battery applications.     

Crystallinity Control of a Nanostructured LiNi0.5Mn1.5O4 Spinel via Polymer‐Assisted Synthesis: A Method for Improving Its Rate Capability and Performance in 5 V Lithium Batteries

Li–Ni–Mn spinels of nominal composition LiNi_0.5Mn_1.5O₄, which are functional materials for electrodes in high‐voltage lithium batteries, are prepared by thermal decomposition of mixed nanocrystalline oxalates obtained by grinding hydrated salts and oxalic acid in the presence of polyethyleneglycol 400. Their structure, microstructure, and texture are established from combined X‐ray photoelectron spectroscopy (XPS), X‐ray diffraction, transmission electron microscopy (TEM), IR spectroscopy, and N₂ absorption measurements. The polymer tailors the shape of particles, which adopt a nanorodlike morphology at low temperatures (400 °C). In fact, the nanorods consist of highly distorted oriented nanocrystals connected by a polymer‐based film as inferred from IR and XPS spectra. The electrochemical properties of spinels in this peculiar form are quite poor, mainly as a result of the high microstrain content of their nanocrystals. Raising the temperature up to 800 °C partially destroys the nanorods, which become highly crystalline nanoparticles approximately 80 nm in size. At this temperature, the polymer facilitates crystal growth; this leads to highly crystalline polyhedral nanoparticles as revealed from TEM images and microstrain data. Following functionalization as a cathode in lithium cells, this material exhibits a very good rate capability, coulombic efficiency, and capacity retention even upon cycling at voltages as high as 5 V. Moreover, it withstands fast‐charge–slow‐discharge processes, which is an important cycle‐life‐related property for commercial batteries.     

Homogeneous CoO on Graphene for Binder‐Free and Ultralong‐Life Lithium Ion Batteries

Ultralong cycle life, high energy, and power density rechargeable lithium‐ion batteries are crucial to the ever‐increasing large‐scale electric energy storage for renewable energy and sustainable road transport. However, the commercial graphite anode cannot perform this challenging task due to its low theoretical capacity and poor rate‐capability performance. Metal oxides hold much higher capacity but still are plagued by low rate capability and serious capacity degradation. Here, a novel strategy is developed to prepare binder‐free and mechanically robust CoO/graphene electrodes, wherein homogenous and full coating of β‐Co(OH)₂ nanosheets on graphene, through a novel electrostatic induced spread growth method, plays a key role. The combined advantages of large 2D surface and moderate inflexibility of the as‐obtained β‐Co(OH)₂/graphene hybrid enables its easy coating on Cu foil by a simple layer‐by‐layer stacking process. Devices made with these electrodes exhibit high rate capability over a temperature range from 0 to 55 °C and, most importantly, maintain excellent cycle stability up to 5000 cycles even at a high current density.     

Single‐Crystalline LiMn2O4 Nanotubes Synthesized Via Template‐Engaged Reaction as Cathodes for High‐Power Lithium Ion Batteries

Single‐crystalline nanotubes of spinel LiMn₂O₄ with a diameter of about 600 nm, a wall thickness of about 200 nm and a length of 1–4 μm have been synthesized via a template‐engaged reaction using β‐MnO₂ nanotubes as a self‐sacrifice template. In this fabrication, a minimal structural reorganization can be responsible for the chemical transformation from [001]‐oriented β‐MnO₂ template to [110]‐oriented LiMn₂O₄. Galvanostatic charge/discharge measurements indicate that the nanotubes exhibit superior high‐rate capabilities and good cycling stability. About 70% of its initial capacity can be retained after 1500 cycles at 5 C rate. Importantly, the tubular nanostructures and the single‐crystalline nature of the most LiMn₂O₄ nanotubes are also well preserved after prolonged charge/discharge cycling at a relatively high current density, indicating good structural stability of the single‐crystalline nanotubes during lithium intercalation/deintercalation process. As is confirmed from Raman spectra analyses, no evident microstructural changes occur upon long‐term cycling. These results reveal that single‐crystalline nanotubes of LiMn₂O₄ will be one of the most promising cathode materials for high‐power lithium ion batteries.     

Liquid‐Crystalline Electrolytes for Lithium‐Ion Batteries: Ordered Assemblies of a Mesogen‐Containing Carbonate and a Lithium Salt

Thermotropic liquid‐crystalline (LC) electrolytes for lithium‐ion batteries are developed for the first time. A rod‐like LC molecule having a cyclic carbonate moiety is used to form self‐assembled two‐dimensional ion‐conductive pathways with lithium salts. Electrochemical and thermal stability, and efficient ionic conduction is achieved for the liquid crystal. The mixture of the carbonate derivative and lithium bis(trifluoromethylsulfonyl)imide is successfully applied as an electrolyte in lithium‐ion batteries. Reversible charge–discharge for both positive and negative electrodes is observed for the lithium‐ion batteries composed of the LC electrolyte.     

Nanophase ZnCo2O4 as a High Performance Anode Material for Li‐Ion Batteries

ZnCo₂O₄ has been synthesized by the low‐temperature and cost‐effective urea combustion method. X‐ray diffraction (XRD), HR‐TEM and selected area electron diffraction (SAED) studies confirmed its formation in pure and nano‐phase form with particle size ～ 15–20 nm. Galvanostatic cycling of nano‐ZnCo₂O₄ in the voltage range 0.005–3.0 V versus Li at 60 mA g^–1 gave reversible capacities of 900 and 960 mA h g^–1, when cycled at 25 °C and 55 °C, respectively. These values correspond to ～ 8.3 and ～ 8.8 mol of recyclable Li per mole of ZnCo₂O₄. Almost stable cycling performance was exhibited in the range 5–60 cycles at 60 mA g^–1 and at 25 °C with ～ 98 % coulombic efficiency. A similar cycling stability at 55 °C, and good rate‐capability both at 25 and 55 °C were found. The average discharge‐ and charge‐potentials were ～ 1.2 V and ～ 1.9 V, respectively. The ex‐situ‐XRD, ‐HRTEM, ‐SAED and galvanostatic cycling data are consistent with a reaction mechanism for Li‐recyclability involving both de‐alloying‐alloying of Zn and displacement reactions, viz., LiZn ? Zn ? ZnO and Co ? CoO ? Co₃O₄. For the first time we have shown that both Zn‐ and Co‐ions act as mutual beneficial matrices and reversible capacity contribution of Zn through both alloy formation and displacement reaction takes place to yield stable and high capacities. Thus, nano‐ZnCo₂O₄ ranks among the best oxide materials with regard to Li‐recyclability.     

Cubic Perovskite Fluoride as Open Framework Cathode for Na‐Ion Batteries

Exploring novel structure prototype and mineral phase, especially open framework material, is crucial to developing high‐performance Na‐ion battery cathodes in view of potentially faster intrinsic diffusion of Na⁺ in lattices. Perovskite phases have been widely applied in solar cells, fuel cells, and electrocatalysis; however, they are rarely attempted as energy storage electrode materials. This study proposes pre‐expanding perovskite iron fluoride (KFeF₃) framework by stuffing large‐sized K⁺ as a channel filler, which is advantageous over Na⁺, NH₄⁺, and H₂O molecule filler in terms of structure robustness, symmetry, and connectivity. K⁺ stuffing leads to the preservation of a more “regular” cubic phase with fast isotropic 3D diffusion as a consequence of no distortion of FeF₆ octahedra during K‐Na electrochemical exchange and following Na‐insertion cycling. High‐rate Na‐storage is achievable with a reversible capacity of 110, 70, and 40 mAh g^?1 at 0.1, 2, and 10 C, respectively, for this open framework fluoride cathode, benefiting from solid solution electrochemical behavior and high intrinsic diffusion coefficient. It is thought that this rate performance is currently the best among Na‐storage fluoride materials.     

High‐Performance Olivine for Lithium Batteries: Effects of Ni/Co Doping on the Properties of LiFeαNiβCoγPO4 Cathodes

New high voltage and high capacity storage systems are needed to sustain the increasing energy demand set by the portable electronics and auto­motive fields. Due to their good electrochemical performance, lithium‐transition metal‐phosphates (LiMPO₄) seem to be very attractive as cathode materials for lithium secondary batteries. Here the synthesis and the characterization of five high voltage cathodes for lithium batteries, based on lithium–iron, lithium–nickel, lithium–cobalt phosphates are described. The effect of differing degrees of cobalt and nickel doping on structure, morphology, and the electrochemical properties of the different materials is thoroughly studied. Transition metal atoms in these materials are found to be vicariant within the olivine crystal structure; however, the lattice parameters and cell volume can be modulated by varying the nickel/cobalt ratio during the synthesis. High performance battery prototypes in terms of voltage (>4.0 V), specific capacity (125 mAh g^?1), specific energy (560 mWh g^?1), and cyclic life (>150 cycles) are also demonstrated.     

Potassium Prussian Blue Nanoparticles: A Low‐Cost Cathode Material for Potassium‐Ion Batteries

Potassium‐ion batteries (KIBs) in organic electrolytes hold great promise as an electrochemical energy storage technology owing to the abundance of potassium, close redox potential to lithium, and similar electrochemistry with lithium system. Although carbon materials have been studied as KIB anodes, investigations on KIB cathodes have been scarcely reported. A comprehensive study on potassium Prussian blue K_0.220Fe[Fe(CN)₆]_0.805?4.01H₂O nanoparticles as a potential cathode material is for the first time reported. The cathode exhibits a high discharge voltage of 3.1–3.4 V, a high reversible capacity of 73.2 mAh g^?1, and great cyclability at both low and high rates with a very small capacity decay rate of ≈0.09% per cycle. Electrochemical reaction mechanism analysis identifies the carbon‐coordinated Fe^III/Fe^II couple as redox‐active site and proves structural stability of the cathode during charge/discharge. Furthermore, for the first time, a KIB full‐cell is presented by coupling the nanoparticles with commercial carbon materials. The full‐cell delivers a capacity of 68.5 mAh g^?1 at 100 mA g^?1 and retains 93.4% of the capacity after 50 cycles. Considering the low cost and material sustainability as well as the great electrochemical performances, this work may pave the way toward more studies on KIB cathodes and trigger future attention on rechargeable KIBs.     

Rational Molecular Design of Benzoquinone‐Derived Cathode Materials for High‐Performance Lithium‐Ion Batteries

p‐Benzoquinone (BQ) is a promising cathode material for lithium‐ion batteries (LIBs) due to its high theoretical specific capacity and voltage. However, it suffers from a serious dissolution problem in organic electrolytes, leading to poor electrochemical performance. Herein, two BQ‐derived molecules with a near‐plane structure and relative large skeleton: 1,4‐bis(p‐benzoquinonyl)benzene (BBQB) and 1,3,5‐tris(p‐benzoquinonyl)benzene (TBQB) are designed and synthesized. They show greatly decreased solubility as a result of strong intermolecular interactions. As cathode materials for LIBs, they exhibit high carbonyl utilizations of 100% with high initial capacities of 367 and 397 mAh g^?1, respectively. Especially, BBQB with better planarity presents remarkably improved cyclability, retaining a high capacity of 306 mAh g^?1 after 100 cycles. The cycling stability of BBQB surpasses all reported BQ‐derived small molecules and most polymers. This work provides a new molecular structure design strategy to suppress the dissolution of organic electrode materials for achieving high performance rechargeable batteries.     

Synthesis of Hierarchically Porous Carbon Monoliths with Highly Ordered Microstructure and Their Application in Rechargeable Lithium Batteries with High‐Rate Capability

In this paper, we report on Li storage in hierarchically porous carbon monoliths with a relatively higher graphite‐like ordered carbon structure. Macroscopic carbon monoliths with both mesopores and macropores were successfully prepared by using meso‐/macroporous silica as a template and using mesophase pitch as a precursor. Owing to the high porosity (providing ionic transport channels) and high electronic conductivity (ca. 0.1 S cm^–1), this porous carbon monolith with a mixed conducting 3D network shows a superior high‐rate performance if used as anode material in electrochemical lithium cells. A challenge for future research as to its applicability in batteries is the lowering of the irreversible capacity.     

Layer‐Based Heterostructured Cathodes for Lithium‐Ion and Sodium‐Ion Batteries

A critical bottleneck that hinders major performance improvement in lithium‐ion and sodium‐ion batteries is the inferior electrochemical activity of their cathode materials. While significant research progresses have been made, conventional single‐phase cathodes are still limited by intrinsic deficiencies such as low reversible capacity, enormous initial capacity loss, rapid capacity decay, and poor rate capability. In the past decade, layer‐based heterostructured cathodes acquired by combining multiple crystalline phases have emerged as candidates with a huge potential to realize performance breakthrough. Herein, recent studies on the structural properties, electrochemical behaviors, and synthesis route optimizations of these heterostructured cathodes are summarized for in‐depth discussions. Particular attention is paid to the latest mechanism discoveries and performance achievements. This review thus aims to promote a deeper understanding of the correlation between the crystal structure of cathodes and their electrochemical behavior, and offers guidance to design advance cathode materials from the aspect of crystal structure engineering.     

Fabrication of Electrospinning‐Derived Carbon Nanofiber Webs for the Anode Material of Lithium‐Ion Secondary Batteries

A carbon nanofiber‐based electrode, exhibiting a large accessible surface area (derived from the nanometer‐sized fiber diameter), high carbon purity (without binder), relatively high electrical conductivity, structural integrity, thin web macromorphology, a large reversible capacity (ca. 450 mA h g^–1), and a relatively linearly inclined voltage profile, is fabricated by nanofiber formation via electrospinning of a polymer solution and its subsequent thermal treatment. It is envisaged that these characteristics of this novel carbon material will make it an ideal candidate for the anode material of high‐power lithium‐ion batteries (where a high current is critically needed), owing to the highly reduced lithium‐ion diffusion path within the active material.     

Sustainable Separators for High‐Performance Lithium Ion Batteries Enabled by Chemical Modifications

Natural polymer nanofibers are attractive sustainable raw materials to fabricate separators for high‐performance lithium ion batteries (LIBs). Unfortunately, complicated pore‐forming processes, low ionic conductivity, and relatively low mechanical strength of previously reported natural polymer nanofiber‐based separators severely limit their performances and applications. Here, a chemical modification strategy to endow high performance to natural polymer nanofiber‐based separators is demonstrated by grafting cyanoethyl groups on the surface of chitin nanofibers. The fabricated cyanoethyl‐chitin nanofiber (CCN) separators not only exhibit much higher ionic conductivity but also retain excellent mechanical strength in comparison to unmodified chitin nanofiber separators. Through density function theory calculations, the mechanism of high Li⁺ ion transport in the CCN separator is unraveled as weakening of the binding of Li⁺ ions over that of PF₆^? ions with chitin, via the cyanoethyl modification. The LiFePO₄/Li₄Ti₅O₁₂ full cells using CCN separators show much better rate capability and enhanced capacity retention compared to the cell using commercial polypropylene (PP) separators. Beyond this, the CCN separator can work very well even at an elevated temperature of 120 °C in the LiFePO₄/Li cell. The proposed strategy chemical modification of natural polymer nanofibers will open a new avenue to fabricate sustainable separators for LIBs with superior performance.