Enhanced Rate Capability and Low-Temperature Performance of Li4Ti5O12 Anode Material by Facile Surface Fluorination

Structural Engineering of Anode Materials for Low-Temperature Lithium-Ion Batteries: Mechanisms, Strategies, and Prospects

The severe degradation of electrochemical performance for lithium-ion batteries (LIBs) at low temperatures poses a significant challenge to their practical applications. Consequently, extensive efforts have been contributed to explore novel anode materials with high electronic conductivity and rapid Li+ diffusion kinetics for achieving favorable low-temperature performance of LIBs. Herein, we try to review the recent reports on the synthesis and characterizations of low-temperature anode materials. First, we summarize the underlying mechanisms responsible for the performance degradation of anode materials at subzero temperatures. Second, detailed discussions concerning the key pathways (boosting electronic conductivity, enhancing Li+ diffusion kinetics, and inhibiting lithium dendrite) for improving the low-temperature performance of anode materials are presented. Third, several commonly used low-temperature anode materials are briefly introduced. Fourth, recent progress in the engineering of these low-temperature anode materials is summarized in terms of structural design, morphology control, surface & interface modifications, and multiphase materials. Finally, the challenges that remain to be solved in the field of low-temperature anode materials are discussed. This review was organized to offer valuable insights and guidance for next-generation LIBs with excellent low-temperature electrochemical performance.

Critical Review on Low-Temperature Li-Ion/Metal Batteries

With the highest energy density ever among all sorts of commercialized rechargeable batteries, Li-ion batteries (LIBs) have stimulated an upsurge utilization in 3C devices, electric vehicles, and stationary energy-storage systems. However, a high performance of commercial LIBs based on ethylene carbonate electrolytes and graphite anodes can only be achieved at above -20 °C, which restricts their applications in harsh environments. Here, a comprehensive research progress and in-depth understanding of the critical factors leading to the poor low-temperature performance of LIBs is provided; the distinctive challenges on the anodes, electrolytes, cathodes, and electrolyte-electrodes interphases are sorted out, with a special focus on Li-ion transport mechanism therein. Finally, promising strategies and solutions for improving low-temperature performance are highlighted to maximize the working-temperature range of the next-generation high-energy Li-ion/metal batteries.

TiO2(B) nanosheets modified Li4Ti5O12microsphere anode for high-rate lithium-ion batteries

With the increasing applications of Lithium-ion batteries in heavy equipment and engineering machinery, the requirements of rate capability are continuously growing. The high-rate performance of Li₄Ti₅O₁₂(LTO) needs to be further improved. In this paper, we synthesized LTO microsphere-TiO₂(B) nanosheets (LTO-TOB) composite by using a solvothermal method and subsequent calcination. LTO-TOB composite combines the merits of TiO₂(B) and LTO, resulting in excellent high-rate capability (144.8, 139.3 and 124.4 mAh g^-1at 20 C, 30 C and 50 C) and superior cycling stability (98.9% capability retention after 500 cycles at 5 C). Its excellent electrochemical properties root in the large surface area, high grain-boundary density and pseudocapacitive effect of LTO-TOB. This work reveals that LTO-TOB composite can be a potential anode for high power and energy density lithium-ion batteries.

Few-layer bismuth selenide cathode for low-temperature quasi-solid-state aqueous zinc metal batteries

The performances of rechargeable batteries are strongly affected by the operating environmental temperature. In particular, low temperatures (e.g., ≤0 °C) are detrimental to efficient cell cycling. To circumvent this issue, we propose a few-layer Bi₂Se₃ (a topological insulator) as cathode material for Zn metal batteries. When the few-layer Bi₂Se₃ is used in combination with an anti-freeze hydrogel electrolyte, the capacity delivered by the cell at −20 °C and 1 A g⁻¹ is 1.3 larger than the capacity at 25 °C for the same specific current. Also, at 0 °C the Zn | |few-layer Bi₂Se₃ cell shows capacity retention of 94.6% after 2000 cycles at 1 A g⁻¹. This behaviour is related to the fact that the Zn-ion uptake in the few-layer Bi₂Se₃ is higher at low temperatures, e.g., almost four Zn²⁺ at 25 °C and six Zn²⁺ at −20 °C. We demonstrate that the unusual performance improvements at low temperatures are only achievable with the few-layer Bi₂Se₃ rather than bulk Bi₂Se₃. We also show that the favourable low-temperature conductivity and ion diffusion capability of few-layer Bi₂Se₃ are linked with the presence of topological surface states and weaker lattice vibrations, respectively.

The performances of rechargeable batteries are detrimentally affected by low temperatures (e.g., < 0 °C). Here, the authors report a few-layer Bi2Se3 material capable of improving battery cycling performances when operational temperatures are shifted from +25 °C to −20 °C.

Polymer-templated mesoporous lithium titanate microspheres for high-performance lithium batteries

The spinel Li4Ti5O12 (LTO) is a promising lithium ion battery anode material with the potential to supplement graphite as an industry standard, but its low electrical conductivity and Li-ion diffusivity need to be overcome. Here, mesoporous LTO microspheres with carbon-coatings were formed by phase separation of a homopolymer from microphase-separated block copolymers of varying molar masses containing sol-gel precursors. Upon heating the composite underwent a sol-gel condensation reaction followed by the eventual pyrolysis of the polymer templates. The optimised mesoporous LTO microspheres demonstrated an excellent electrochemical performance with an excellent specific discharge capacity of 164 mA h g-1, 95% of which was retained after 1000 cycles at a C-rate of 10.

Mechanical Stirring Synthesis of 1D Electrode Materials and Designing of Pyramid/Inverted Pyramid Interlocking for Highly Flexible and Foldable Li-Ion Batteries with High Mass Loading

Flexible and foldable Li-ion batteries (LIBs) are presently attracting immense research interest for their potential use in wearable electronics but are still limited to electrodes with very small mass loading, low bending/folding endurance, and poor electrochemical stability during repeated bending and folding movements. Moreover, one-dimensional (1D) structured electrode materials have shown excellent electrochemical performance but are still restricted by the high cost and complicated fabrication process. Here, we present a very simple yet novel approach for fabricating extra-long Li₄Ti₅O₁₂ (LTO) and LiCoO₂ (LCO) nanofiber precursors by directly stirring the reagents in an atmospheric vessel. In addition, we present multilayer pyramid/inverted pyramid interlocking inside the LTO and LCO nanofiber films as well as between films and current collectors, which can create strengthened interfacial bonding like a zipper and tangentially disperse the strains generated during folding through the pyramidal planes and edges, leading to the realization of thick-film electrodes with outstanding electrochemical stability during folding movements. The foldable LIBs that are assembled with LTO and LCO nanofiber electrodes at a practical level of mass loading (14.9-19.4 mg cm^-2) can maintain 102% of the initial capacity after 15 000 times of fully folding (180°) motions.

Plasma-Introduced Oxygen Defects Confined in Li4Ti5O12 Nanosheets for Boosting Lithium-Ion Diffusion

Although Li₄Ti₅O₁₂ (LTO) is considered as a promising anode material for high-power Li-ion batteries with high safety, the sluggish Li-ion diffusion coefficient restricts its widespread application. In this work, oxygen vacancy was successfully incorporated into LTO by an eco-friendly and cost-effective plasma process. The deficient LTO delivers much higher capacities of 173.4 mAh g^-1 at 1C rate after 100 cycles and 140.5 mAh g^-1 at 5C after 1000 cycles than those of pristine LTO. Meanwhile, even at a high rate of 20C, it displays an ultrahigh capacity of 133.1 mAh g^-1 after 500 cycles with a Coulombic efficiency of 100%. Detailed analysis reveals that the lithium storage mechanisms in the oxygen-deficient LTO, especially at high rate, were dominated by the insertion behavior and dual-phase conversion due to the fast ion-diffusion ability, rather than the widely reported surface capacitance by other approaches. This work highlights that defect generation by plasma in nanomaterials is an effective way to promote ion mobility, especially at high rates, and thus can be extended to other electrode materials for advanced energy-storage applications.

Mechanochemical Synthesis of γ-Graphyne with Enhanced Lithium Storage Performance

γ-Graphyne is a new nanostructured carbon material with large theoretical Li⁺ storage due to its unique large conjugate rings, which makes it a potential anode for high-capacity lithium-ion batteries (LIBs). In this work, γ-graphyne-based high-capacity LIBs are demonstrated experimentally. γ-Graphyne is synthesized through mechanochemical and calcination processes by using CaC₂ and C₆ Br₆ . Brunauer-Emmett-Teller, atomic force microscopy, X-ray photoelectron spectroscopy, solid-state ¹³ C NMR and Raman spectra are conducted to confirm its morphology and chemical structure. The sample presents 2D mesoporous structure and is exactly composed of sp and sp² -hybridized carbon atoms as the γ-graphyne structure. The electrode shows high Li⁺ storage (1104.5 mAh g^-1 at 100 mA g^-1 ) and rate capability (435.1 mAh g^-1 at 5 A g^-1 ). The capacity retention can be up to 948.6 (200 mA g^-1 for 350 cycles) and 730.4 mAh g^-1 (1 A g^-1 for 600 cycles), respectively. These excellent electrochemical performances are ascribed to the mesoporous architecture, large conjugate rings, enlarged interplanar distance, and high structural integrity for fast Li⁺ diffusion and improved cycling stability in γ-graphyne. This work provides an environmentally benign and cost-effective mechanochemical method to synthesize γ-graphyne and demonstrates its superior Li⁺ storage experimentally.

Synergistic Effect of F- Doping and LiF Coating on Improving the High-Voltage Cycling Stability and Rate Capacity of LiNi0.5Co0.2Mn0.3O2 Cathode Materials for Lithium-Ion Batteries

A commercial LiNi_0.5Co_0.2Mn_0.3O₂ (LNCM) cathode material is purposefully modified using a small account of LiPF₆ as one precursor via a simple means at low calcination temperature in air. X-ray diffraction, scanning electron microscopy, and transmission electron microscopy images reveal that this modification process keeps the layered bulk structure of LNCM even though the surface components have obviously been modified. Electron energy loss spectroscopy and X-ray photoelectron spectroscopy with different etching depths further prove the formation of LiF and F^- doping on the LNCM surface, which simultaneously triggers partial Ni³⁺ reduction to Ni²⁺; and the metal-oxygen bond is partially replaced by a higher energy metal-fluorine bond. The modified material (LNCM-2) retains 93.7% of its initial capacity and delivers 179.4 mAh g^-1 at a current density of 0.5 C after 100 stable cycles at 3.0-4.5 V. Meanwhile, LNCM-2 is able to maintain capacity retention up to 81.1% after 300 cycles at 5 C, much better than the original LNCM (35.1%) in the commercial electrolyte. Remarkably, 90% of initial capacity is retained for LNCM-2 with considerably improved Coulombic efficiency (>99.5%) at 5 C after 300 cycles within a voltage range of 3-4.5 V compared with the primary LNCM using succinonitrile-based electrolyte. Consequently, these results fully demonstrate the advantages of synergistic effect between F^- doping and LiF coating.

Octahedral and Porous Spherical Ordered LiNi0.5Mn1.5O4 Spinel: the Role of Morphology on Phase Transition Behavior and Electrode/Electrolyte Interfacial Properties

LiNi_0.5Mn_1.5O₄ compound as positive electrode of the lithium ion battery with high specific energy or high specific power, has a good application prospect in the field of electric vehicles such as PHEV/EVs. The influence of the morphology of ordered LiNi_0.5Mn_1.5O₄ on phase transition behavior and electrode/electrolyte interfacial properties is investigated, including octahedral and porous spherical morphologies. Three phases named LiNi_0.5Mn_1.5O₄ (Li1), Li_0.5Ni_0.5Mn_1.5O₄ (Li0.5) and Ni_0.5Mn_1.5O₄ (Li0) are detected by in situ X-ray diffraction (XRD) measurement with high time resolution in the octahedral and porous spherical ordered LiNi_0.5Mn_1.5O₄ materials during charge and discharge, and the phase transition kinetics of the two samples at high discharge rate and after charge-discharge cycles are elucidated. It is a clear demonstration that the high-rate capability and cycle life of LiNi_0.5Mn_1.5O₄ material are influenced by crystal morphology. The porous spherical LiNi_0.5Mn_1.5O₄ material exhibits better rate performance, associated with the fast reaction kinetic of Li0.5 phase formation. It is noticed that the coexistence of three cubic phases in the initial discharge stage is observed in the cycled octahedral sample, resulting in a higher capacity fading after 200 cycles at room temperature and 1 C. However, the porous spherical sample exhibits a poor cyclic performance at 55 °C and 1 C. This may be attributed to the fact that the porous spherical sample with high specific surface area leads to an accelerated decomposition of the electrolyte at 55 °C, and the thick interfacial film and high content of LiF on the electrode surface are formed.

Smart Construction of Integrated CNTs/Li4Ti5O12 Core/Shell Arrays with Superior High-Rate Performance for Application in Lithium-Ion Batteries

Exploring advanced high-rate anodes is of great importance for the development of next-generation high-power lithium-ion batteries (LIBs). Here, novel carbon nanotubes (CNTs)/Li₄Ti₅O₁₂ (LTO) core/shell arrays on carbon cloth (CC) as integrated high-quality anode are constructed via a facile combined chemical vapor deposition-atomic layer deposition (ALD) method. ALD-synthesized LTO is strongly anchored on the CNTs' skeleton forming core/shell structures with diameters of 70-80 nm the combined advantages including highly conductive network, large surface area, and strong adhesion are obtained in the CC-LTO@CNTs core/shell arrays. The electrochemical performance of the CC-CNTs/LTO electrode is completely studied as the anode of LIBs and it shows noticeable high-rate capability (a capacity of 169 mA h g^-1 at 1 C and 112 mA h g^-1 at 20 C), as well as a stable cycle life with a capacity retention of 86% after 5000 cycles at 10 C, which is much better than the CC-LTO counterpart. Meanwhile, excellent cycling stability is also demonstrated for the full cell with LiFePO₄ cathode and CC-CNTs/LTO anode (87% capacity retention after 1500 cycles at 10 C). These positive features suggest their promising application in high-power energy storage areas.

Scalable in Situ Synthesis of Li4Ti5O12/Carbon Nanohybrid with Supersmall Li4Ti5O12 Nanoparticles Homogeneously Embedded in Carbon Matrix

Li₄Ti₅O₁₂ (LTO) is regarded as a promising lithium-ion battery anode due to its stable cyclic performance and reliable operation safety. The moderate rate performance originated from the poor intrinsic electron and lithium-ion conductivities of the LTO has significantly limited its wide applications. A facile scalable synthesis of hierarchical Li₄Ti₅O₁₂/C nanohybrids with supersmall LTO nanoparticles (ca. 17 nm in diameter) homogeneously embedded in the continuous submicrometer-sized carbon matrix is developed. Difunctional methacrylate monomers are used as solvent and carbon source to generate TiO₂/C nanohybrid, which is in situ converted to LTO/C via a solid-state reaction procedure. The structure, morphology, crystallinity, composition, tap density, and electrochemical performance of the LTO/C nanohybrid are systematically investigated. Comparing to the control sample of the commercial LTO composited with carbon, the reversible specific capacity after 1000 cycles at 175 mA g^-1 and rate performance at high current densities (875, 1750, and 3500 mA g^-1) of the Li₄Ti₅O₁₂/C nanohybrid have been significantly improved. The enhanced electrochemical performance is due to the unique structure feature, where the supersmall LTO nanoparticles are homogeneously embedded in the continuous carbon matrix. Good tap density is also achieved with the LTO/C nanohybrid due to its hierarchical micro-/nanohybrid structure, which is even higher than that of the commercial LTO powder.