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.

Review and prospects on the low-voltage Na_(2)Ti_(3)O_(7) anode materials for sodium-ion batteries

Due to its low cost and natural abundance of sodium,Na-ion batteries(NIBs)are promising candidates for large-scale energy storage systems.The development of ultralow voltage anode materials is of great significance in improving the energy density of NIBs.Low-voltage anode materials,however,are severely lacking in NIBs.Of all the reported insertion oxides anodes,the Na_(2)Ti_(3)O_(7) has the lowest operating voltage(an average potential of 0.3 V vs.Na^(+)/Na)and is less likely to deposit sodium,which has excellent potential for achieving NIBs with high energy densities and high safety.Although significant progress has been made,achieving Na_(2)Ti_(3)O_(7) electrodes with excellent performance remains a severe challenge.This paper systematically summarizes and discusses the physicochemical properties and synthesis methods of Na_(2)Ti_(3)O_(7).Then,the sodium storage mechanisms,key issues and challenges,and the optimization strategies for the electrochemical performance of Na_(2)Ti_(3)O_(7) are classified and further elaborated.Finally,remaining challenges and future research directions on the Na_(2)Ti_(3)O_(7) anode are highlighted.This review offers insights into the design of high-energy and high-safety NIBs.

A review on anode materials for lithium/sodium-ion batteries

Since lithium-ion batteries(LIBs) have been substantially researched in recent years, they now possess exceptional energy and power densities, making them the most suited energy storage technology for use in developed and developing industries like stationary storage and electric cars, etc. Concerns about the cost and availability of lithium have prompted research into alternatives, such as sodium-ion batteries(SIBs), which use sodium instead of lithium as the charge carrier. This is especially relevant for stationary applications, where the size and weight of battery are less important. The working efficiency and capacity of these batteries are mainly dependent on the anode, cathode, and electrolyte. The anode,which is one of these components, is by far the most important part of the rechargeable battery.Because of its characteristics and its structure, the anode has a tremendous impact on the overall performance of the battery as a whole. Keeping the above in view, in this review we critically reviewed the different types of anodes and their performances studied to date in LIBs and SIBs. The review article is divided into three main sections, namely:(i) intercalation reaction-based anode materials;(ii) alloying reaction-based anode materials;and(iii) conversion reaction-based anode materials, which are further classified into a number of subsections based on the type of material used. In each main section, we have discussed the merits and challenges faced by their particular system. Afterward, a brief summary of the review has been discussed. Finally, the road ahead for better application of Li/Na-ion batteries is discussed, which seems to mainly depend on exploring the innovative materials as anode and on the inoperando characterization of the existing materials for making them more capable in terms of application in rechargeable batteries.

Carbon-coated ZnO Nanocomposite Microspheres as Anode Materials for Lithium-ion Batteries

The carbon-coated ZnO nanospheres materials have been synthesized via a simple hydrothermal method.The effect of carbon content on the microstructure,morphology and electrochemical performance of the materials was investigated by XRD,Raman spectroscopy,transmission electron microscopy,scanning electron microscopy and electrochemical techniques.Research results show that the spherical ZnO/C material with a carbon cladding content of 10%is very homogeneous and approximately 200 nm in size.The electrochemical performances of the ZnO/C nanospheres as an anode materials are examines.The ZnO/C exhibits better stability than pure ZnO,excellent lithium storage properties as well as improved circulation performance.The Coulomb efficiency of the ZnO/C with 10%carbon coated content reaches 98%.The improvement of electrochemical performance can be attributed to the carbon layer on the ZnO surface.The large volume change of ZnO during the charge-discharge process can be effectively relieved.

Synthesis of Cu_2O/reduced graphene oxide composites as anode materials for lithium ion batteries

A facile way was used to synthesize Cu2O/reduced graphene oxide （rGO） composites with octahedron-like morphology in aqueous solution without any surfactant. TEM images of the obtained Cu2O/rGOs reveal that the Cu2O particles and rGO distribute hierarchically and the primary Cu2O particles are encapsulated well in the graphene nanosheets. The electrochemical performance of Cu2O/rGOs is enhanced compared with bare Cu2O when they are employed as anode materials for lithium ion batteries. The Cu2O/rGO composites maintain a reversible capacity of 348.4 mA？h/g after 50 cycles at a current density of 100 mA/g. In addition, the composites retain 305.8 mA？h/g after 60 cycles at various current densities of 50, 100, 200, 400 and 800 mA/g.

Recent progress of advanced anode materials of lithium-ion batteries

The rapid development of electric vehicles and mobile electronic devices is the main driving force to improve advanced high-performance lithium ion batteries(LIBs).The capacity,rate performance and cycle stability of LIBs rely directly on the electrode materials.As far as the development of the advanced LIBs electrode is concerned,the improvement of anode materials is more urgent than the cathode materials.Industrial production of anode materials superior to commercial graphite still faces some challenges.This review sets out the most basic LIBs anode material design.The reaction principles and structural design of carbon materials,various transition metal oxides,silicon and germanium are summarized,and then the progress of other anode materials are analyzed.Due to the rapid development of metal organic frameworks(MOFs)in energy storage and conversion in recent years,the synthesis process and energy storage mechanism of nanostructures derived from MOF precursors are also discussed.From the perspective of novel structural design,the progress of various MOFs-derived materials for alleviating the volume expansion of anode materials is discussed.Finally,challenges for the future development of advanced anode materials for LIBs will be considered.

Tempura-like carbon/carbon composite as advanced anode materials for K-ion batteries

Graphite as a promising anode candidate of K-ion batteries(KIBs)has been increasingly studied currently,but corresponding rate performance and cycling stability are usually inferior to amorphous carbon materials.To protect the layer structure and further boost performance,tempura-like carbon/carbon nanocomposite of graphite@pitch-derived S-doped carbon(G@PSC)is designed and prepared by a facile and low-temperature modified molten salt method.This robust encapsulation structure makes their respective advantages complementary to each other,showing mutual promotion of electrochemical performances caused by synergy effect.As a result,the G@PSC electrode is applied in KIBs,delivering impressive rate capabilities(465,408,370,332,290,and 227 m A h g^(-1)at 0.05,0.2,0.5,1,2,and 5 A g^(-1))and ultralong cyclic stability(163 m A g^(-1)remaining even after 8000 cycles at 2 A g^(-1)).On basis of ex-situ studies,the sectionalized K-storage mechanism with adsorption(pseudocapacitance caused by S doping)-intercalation(pitch-derived carbon and graphite)pattern is revealed.Moreover,the exact insights into remarkable rate performances are taken by electrochemical kinetics tests and density functional theory calculation.In a word,this study adopts a facile method to synthesize high-performance carbon/carbon nanocomposite and is of practical significance for development of carbonaceous anode in KIBs.

CoFe_2O_4-Graphene Nanocomposites Synthesized through An Ultrasonic Method with Enhanced Performances as Anode Materials for Li-ion Batteries

Co Fe2O4-graphene nanosheets(Co Fe2O4-GNSs) were synthesized through an ultrasonic method, and their electrochemical performances as Li-ion battery electrode were improved by annealing processes. The nanocomposites obtained at 350 °C maintained a high specific capacity of 1,257 m Ah g-1even after 200 cycles at 0.1 A g-1. Furthermore,the obtained materials also have better rate capability, and it can be maintained to 696, 495, 308, and 254 m Ah g-1at 1, 2,5, and 10 A g-1, respectively. The enhancements realized in the reversible capacity and cyclic stability can be attributed to the good improvement in the electrical conductivity achieved by annealing at appropriate temperature, and the electrochemical nature of Co Fe2O4 and GNSs during discharge–charge processes.

Internal failure of anode materials for lithium batteriesd——A critical review

Prevention of mechanical and finally electrochemical failures of lithium batteries is a critical aspect to be considered during their design and performance, especially for those with high specific capacities. Internal failure is observed as one of the most serious factors, including loss of electrode materials, structure deformation and dendrite growth. It usually incubates from atomic/molecular level and progressively aggravates along with lithiation. Understanding the internal failure is of great importance for developing solutions of failure prevention and advanced anode materials. In this research, different internal failure processes of anode materials for lithium batteries are discussed. The progress on observation technologies of the anode failure is further summarized in order to understand their mechanisms of internal failure. On top of them, this review aims to summarize innovative methods to investigate the anode failure mechanisms and to gain new insights to develop advanced and stable anodes for lithium batteries.

Bi nanoparticles in situ encapsulated by carbon film as high-performance anode materials for Li-ion batteries

Bismuth (Bi) has indeed inspired great interests in lithium-ion batteries (LIBs) due to the high capacity,but was still limited by the low electrical conductivity and large volume variation.Herein,a composite material based on Bi nanoparticles in situ encapsulated by carbon film (Bi@CF) is prepared successfully through a facile metal–organic framework (MOF)-engaged approach.As anode materials for LIBs,the Bi@CF composites achieved high reversible capacities of 705 and 538 mAh g^(-1)at 0.2 and 0.5 A g^(-1) after200 cycles,and long cycling performance with a stable capacity of 306 mAh g^(-1)at 1.0 A g^(-1) even after 900 cycles.In situ X-ray diffraction (XRD) measurements clearly revealed the conversion between Bi and Li_(3)Bi during the alloying/dealloying process,confirming the good electrochemical reversibility of Bi@CF for Li-storage.The reaction kinetics of this Bi@CF composite was further studied by galvanostatic intermittent titration technique (GITT).This work may provide an inspiration for the elaborate design and facile preparation of alloy-type anode materials for high-performance rechargeable batteries.

Nitrogen-Doped TiO_2–C Composite Nanofibers with High-Capacity and Long-Cycle Life as Anode Materials for Sodium-Ion Batteries

Nitrogen-doped TiO_2–C composite nanofibers(TiO_2/N–C NFs) were manufactured by a convenient and green electrospinning technique in which urea acted as both the nitrogen source and a pore-forming agent. The TiO_2/N–C NFs exhibit a large specific surface area(213.04 m^2 g^(-1)) and a suitable nitrogen content(5.37 wt%). The large specific surface area can increase the contribution of the extrinsic pseudocapacitance, which greatly enhances the rate capability. Further, the diffusion coefficient of sodium ions(DNa_+) could be greatly improved by the incorporation of nitrogen atoms. Thus, the TiO_2/N–C NFs display excellent electrochemical properties in Na-ion batteries. A TiO_2/N–C NF anode delivers a high reversible discharge capacity of 265.8 mAh g^(-1) at 0.05 A g^(-1) and an outstanding long cycling performance even at a high current density(118.1 m Ah g^(-1)) with almost no capacity decay at 5 A g^(-1) over 2000 cycles. Therefore, this work sheds light on the application of TiO_2-based materials in sodium-ion batteries.

Anode materials for potassium-ion batteries: Current status and prospects

Potassium-ion batteries(KIBs)as one of the most promising alternatives to lithium-ion batteries have been highly valued in recent years.However,progress in KIBs is largely restricted by the sluggish development in anode materials.Therefore,it is imperative to systematically outline and evaluate the recent research advances in the field of anode materials for KIBs toward promoting the development of high-performance anode materials for KIBs.In this review,the recent achievements in anode materials for KIBs are summarized.The electrochemical properties(ie.charge storage mechanism,capacity,rate performance,and cycling stability)of these reported anode materials,as well as their advantages/disadvantages,are discerned and analyzed,enabling high-performance KIBs to meet the requirements for practical applications.Finally,technological developments,scientific challenges,and future research opportunities of anode materials for KIBs are briefly reviewed.

Rational Design of WO_3 Nanostructures as the Anode Materials for Lithium-Ion Batteries with Enhanced Electrochemical Performance

A facile, one-step hydrothermal method was employed to synthesize two kinds of WO3 nanostructures. By using different kinds of sylvine, tungsten trioxide(WO3) with different morphologies of microflowers and nanowires was obtained, respectively. The discharge capacities for microflowers and nanowires are 107 and 146 m Ah g-1 after 180 cycles, and their corresponding capacity retentions after the first cycle are 72 and 85 %, respectively. Even at a high current density of 1,600 m Ah g-1, the discharge capacities of WO3 microflowers and nanowires are as high as 433 and557 m Ah g-1 after 40 cycles, in which the current densities were increased stepwise. It is worth mentioned that the rate capability of the nanowires is superior to that of the microflowers. However, the cycle performance of the microflowers is better than nanowires, revealing that the morphology and structure of the as-synthesized WO3 products can exert great influence on the electrochemical performances.

A review on current anode materials for rechargeable Mg batteries

There is an increasing demand for rechargeable batteries in high-performance energy storage systems.The current dominating Li-ion batteries are limited by price,resource availability,as well as their theoretical capacities.So that the community has started to explore alternative battery chemistries.As a promising multivalent battery type,rechargeable magnesium batteries(RMBs)have attracted increasing attention because of high safety,high volumetric energy density,and low cost thanks to abundant resource of Mg.However,the development of high-performance anodes is still hampered by formation of passivating layers on the Mg surface.Additionally,dendrites can also grow under certain conditions with pure Mg anodes,which requires further studies for reliable operation window and substitutes.Therefore,this review specifically aims to provide an overview on the often overlooked yet very important anode materials of RMBs,with the hope to inspire more attention and research efforts for the achievement of over-all better performance of future RMBs.c 2020 Published by Elsevier B.V.on behalf of Chongqing University.

Recent Research Progress of Anode Materials for Potassium-ion Batteries

The next-generation smart grid for the storage and delivery of renewable energy urgently needs to develop a low-cost and rechargeable energy storage technology beyond lithium-ion batteries(LIBs).Owing to the abundance of potassium(K) resources and the similar electrochemical performance to that of LIBs,potassium-ion batteries(PIBs) have been attracted considerable interest in recent years,and significant progress has been achieved concerning the discovery of high-performance electrode materials for PIBs.This review especially summarizes the latest research progress regarding anode materials for PIBs,including carbon materials,organic materials,alloys,metal-based compounds,and other new types of compounds.The reversible K-ion storage principle and the electrochemical performance(i.e.,capacity,potential,rate capability,and cyclability) of these developed anode materials are summarized.Furthermore,the challenges and the corresponding effective strategies to enhance the battery performance of the anode materials are highlighted.Finally,prospects of the future development of high-performance anode materials for PIBs are discussed.

Electrochemical properties of SnO_2 nanorods as anode materials in lithium-ion battery

Well-dispersed SnO2 nanorods with diameter of 4-15 nm and length of 100-200 nm are synthesised through a hydrothermal route and their potential as anode materials in lithium-ion batteries is investigated. The observed initial discharge capacity is as high as 1778 mA.h/g, much higher than the theoretical value of the bulk SnO2 （1494 mA.h/g）. During the following 15 cycles, the reversible capacity decreases from 929 to 576 mA-h/g with a fading rate of 3.5% per cycle. The fading mechanism is discussed. Serious capacity fading can be avoided by reducing the cycling voltages from 0.05-3.0 to 0.4-1.2 V. At the end, SnO2 nanorods with much smaller size are synthesized and their performance as anode materials is studied. The size effect on the electrochemical properties is briefly discussed.

Ultrasonic synthesis of CoO/graphene nanohybrids as high performance anode materials for lithium-ion batteries

A facile ultrasonic method was used to synthesize CoO/graphene nanohybrids by employing Co4（CO）12 as a cobalt precursor. The nanohybrids were characterized by SEM, TEM and XPS, and the results show that CoO nanoparticles （3-5 nm） distribute uniformly on the surface of graphene. The CoO/graphene nanohybrids display high performance as an anode material for lithium-ion battery, such as high reversible lithium storage capacity （650 mA-h/g after 50 cycles, almost twice that of commercial graphite anode）, high coulombic efficiency （over 95%） and excellent cycling stability. The extraordinary performance arises from the structure of the nanohybrids： the nanosized CoO particles with high dispersity on conductive graphene substrates are beneficial for lithium-ion insertion/extraction, shortening diffusion length for lithium ions and improving conductivity, thus the lithium storage performance was improved.

TiO_2/graphene nanocomposites as anode materials for high rate lithium-ion batteries

A simple strategy to prepare a hybrid of nanocomposites of anatase TiO2/graphene nanosheets （GNS） as anode materials for lithium-ion batteries was reported.The morphology and crystal structure were studied by X-ray diffraction （XRD）,field emission scanning electron microscopy （FE-SEM） and transmission electron microscopy （TEM）.The electrochemical performance was evaluated by galvanostatic charge-lischarge tests and alternating current （AC） impedance spectroscopy.The results show that the TiO2/GNS electrode exhibit higher electrochemical performance than that of TiO2 electrode regardless of the rate.Even at 500 mA/g,the capacity of TiO2/GNS is 120.3 mAh/g,which is higher than that of TiO2 61.6 mAh/g.The high performance is attributed to the addition of graphene to improve electrical conductivity and reduce polarization.

Template-Free Synthesis of Sb_2S_3 Hollow Microspheres as Anode Materials for Lithium-Ion and Sodium-Ion Batteries

Hierarchical Sb_2S_3 hollow microspheres assembled by nanowires have been successfully synthesized by a simple and practical hydrothermal reaction. The possible formation process of this architecture was investigated by X-ray diffraction, focused-ion beam-scanning electron microscopy dual-beam system, and transmission electron microscopy. When used as the anode material for lithium-ion batteries, Sb_2S_3 hollow microspheres manifest excellent rate property and enhanced lithium-storage capability and can deliver a discharge capacity of 674 m Ah g^(-1) at a current density of 200 m A g^(-1) after 50 cycles. Even at a high currentdensity of 5000 m A g^(-1), a discharge capacity of541 m Ah g^(-1) is achieved. Sb_2S_3 hollow microspheres also display a prominent sodium-storage capacity and maintain a reversible discharge capacity of 384 m Ah g^(-1) at a current density of 200 m A g^(-1) after 50 cycles. The remarkable lithium/sodium-storage property may be attributed to the synergetic effect of its nanometer size and three-dimensional hierarchical architecture, and the outstanding stability property is attributed to the sufficient interior void space,which can buffer the volume expansion.

Effects of carbon sources on electrochemical performance of Li_4Ti_5O_(12)/C composite anode materials

Li4Ti5O12/C composite materials were synthesized by two-step solid state reaction method with glucose, sucrose, and starch as carbon sources, respectively. The effects of carbon sources on the structure, morphology, and electrochemical performance of Li4Ti5O12/C composite materials were investigated by SEM, XRD and electrochemical tests. The results indicate that carbon sources have almost no effect on the structure of Li4Ti5O12/C composite materials. The initial discharge capacities of the Li4Ti1O12/C composite materials are slightly lower than those of as-synthesized Li4Ti5O12. However, Li4Ti5O12/C composite materials show better electrochemical rate performance than the as-synthesized Li4Ti5O12. The capacity retention （79%） of the Li4Ti5O12/C composite materials with starch as carbon source, is higher than that of Li4Ti5O12/C composite materials with glucose and sucrose as carbon source at current rate of 2.0C.