Li-rich layered oxides: Structure,capacity and voltage fading mechanisms and solving strategies

Lithium rich layered oxides (LLOs) are attractive cathode materials for Li-ion batteries owing to their high capacity (>250 mA h g^–1) and suitable voltage (∼3.6 V). However, they suffer from serious voltage and capacity fading, which is focused in this review. First, an overview of crystal structure, band structure and electrochemical performances of LLOs is provided. After that, current understanding on oxygen loss, capacity fading and voltage fading is summarized. Finally, five strategies to mitigate capacity and voltage fading are reviewed. It is believed that these understandings can help solve the fading problems of LLOs.     

Li-rich layered oxides:Structure,capacity and voltage fading mechanisms and solving strategies

Lithium rich layered oxides (LLOs) are attractive cathode materials for Li-ion batteries owing to their high capacity (＞250 mA h g-1) and suitable voltage (～3.6...     

Solid-state synthesis of Li[Li0.2Mn0.56Ni0.16Co0.08]O2 cathode materials for lithium-ion batteries

Layered Li[Li_0.2Mn_0.56Ni_0.16Co_0.08]O₂ cathode materials were synthesized via a solid-state reaction for Li-ion batteries, in which lithium hydroxide monohydrate, manganese dioxide, nickel monoxide, and cobalt monoxide were employed as metal precursors. To uncover the relationship between the structure and electrochemical properties of the materials, synthesis conditions such as calcination temperature and time as well as quenching methods were investigated. For the synthesized Li[Li_0.2Mn_0.56Ni_0.16Co_0.08]O₂ materials, the metal components were found to be in the form of Mn⁴⁺, Ni²⁺, and Co³⁺, and their molar ratio was in good agreement with stoichiometric ratio of 0.56:0.16:0.08. Among them, the one synthesized at 800 °C for 12 h and subsequently quenched in air showed the best electrochemical performances, which had an initial discharge specific capacity and coulombic efficiency of 265.6 mAh/g and 84.0%, respectively, and when cycled at 0.5, 1, and 2 C, the corresponding discharge specific capacities were 237.3, 212.6, and 178.6 mAh/g, respectively. After recovered to 0.1 C rate, the discharge specific capacity became 259.5 mAh/g and the capacity loss was only 2.3% of the initial value at 0.1 C. This work suggests that the solid-state synthesis route is easy for preparing high performance Li[Li_0.2Mn_0.56Ni_0.16Co_0.08]O₂ cathode materials for Li-ion batteries.     

Solid-state synthesis of Li[Li_(0.2)Mn_(0.56)Ni_(0.16)Co_(0.08)]O_2 cathode materials for lithium-ion batteries

Layered Li|Li_(0.2)Mn_(0.56)Ni_(0.16)Co_(0.08]O_2 cathode materials were synthesized via a solid-state reaction for Liion batteries,in which lithium hydroxide monohydrate,manganese dioxide,nickel monoxide,and cobalt monoxide were employed as metal precursors.To uncover the relationship between the structure and electrochemical properties of the materials,synthesis conditions such as calcination temperature and time as well as quenching methods were investigated.For the synthesized Li[Li_(0.2)Mn_(0.56)Ni_(0.16)Co_(0.08)]O_2materials,the metal components were found to be in the form of Mn~(4+),Ni~(2+),and Co~(3+),and their molar ratio was in good agreement with stoichiometric ratio of 0.56:0.16:0.08.Among them,the one synthesized at 800 C for 12 h and subsequently quenched in air showed the best electrochemical performances,which had an initial discharge specific capacity and coulombic efficiency of 265.6 mAh/g and 84.0%,respectively,and when cycled at 0.5,1,and 2C,the corresponding discharge specific capacities were 237.3,212.6.and 178.6 mAh/g,respectively.After recovered to 0.1 C rate,the discharge specific capacity became259.5 mAh/g and the capacity loss was only 2.3% of the initial value at 0.1 C.This work suggests that the solid-state synthesis route is easy for preparing high performance Li[Li_(0.2)Mn_(0.56)Ni_(0.16)Co_(0.08)]O_2 cathode materials for Li-ion batteries.     

Integrating trace Ti-doping and LiYO2-coating to stabilize Ni-rich cathodes for lithium-ion batteries

Ni-rich layered cathodes have become the promising candidates for the next-generation high-energy Li-ion batteries due to their high energy density and competitive cost. However, they suffer from rapid capacity fading due to the structural and interfacial instability upon long-term operation. Herein, the Ti-doped and LiYO₂-coated Ni-rich layered cathode has been synthesized via a facile one-step sintering strategy, which significantly restrains the interfacial parasitic side reactions and enhances the structural stability. Specifically, the trace Ti⁴⁺ doping greatly stabilizes the lattice oxygen and alleviates the Li/Ni disorder while the LiYO₂ coating layer can prevent the erosion of the cathode by the electrolyte during cycles. As a result, the Ti-NCM83@LYO delivers a high specific capacity of 135 mAh g⁻¹ even at 10C and there is almost no capacity loss at 1C for 100 cycles. This work provides a simple one-step dual-modification strategy to meet the commercial requirements of Ni-rich cathodes.     

Particulate modification of lithium-ion battery anode materials and electrolytes

Lithium-ion batteries (LIBs) are considered a rechargeable and commercial energy storage device for electronic equipment such as smartphone and electric vehicles. Despite the prospective future of LIBs, unsatisfied electrochemical properties like reversible capacity, cycle ability and coulombic efficiency still hinder their development. High volume expansion rate, uncontrolled Li dendrite growth and unsatisfied solid electrolyte interphase also occur when LIBs are applied in long-time usage. Numerous modification methods such as exploring high-capacity anode/cathode materials, constructing artificial solid electrolyte interphase and improved conductive binders can be adopted to enhance the performances. Among them, particulate modification for LIBs anode and electrolytes is receiving tremendous attraction in the recent work. The method is composed of changing the morphology and particle size of the active materials, also introduce nano-size additives to the main structure. This review emphasizes on introducing and discussing the modification in following aspects: particulate modification on carbon group IVA element anodes, introduction of additives like transition metal oxide nanoparticles into anode and electrolyte materials, dissipate the influence of Li dendrite growth and ameliorate the performances of solid electrolyte interface. This review hopes to be denoted for the future development of LIBs with the comprehensive understanding on the particulate modification.     

Electrochemical performance of polygonized carbon nanofibers as anode materials for lithium-ion batteries

Carbon nanofibers with a polygonal cross section (P-CNFs) synthesized using a catalytic chemical vapor deposition (CCVD) technology have been investigated for potential applications in lithium batteries as anode materials. P-CNFs exhibit excellent high-rate capabilities. At a current density as high as 3.7 and 7.4 A/g, P-CNFs can still deliver a reversible capacity of 198.4 and 158.2 mAh/g, respectively. To improve their first coulombic efficiency, carbon-coated P-CNFs were prepared through thermal vapor deposition (TVD) of benzene at 900 °C. The electrochemical results demonstrate that appropriate amount of carbon coating can improve the first coulombic efficiency, the cycling stability and the rate performance of P-CNFs. After carbon coating, P-CNFs gain a weight increase approximately by 103 wt%, with its first coulombic efficiency increasing from 63.1 to 78.4%, and deliver a reversible capacity of 197.4 mAh/g at a current density of 3.7 A/g. After dozens of cycles, there is no significant capacity degradation at both low and high current densities.     

轻便电源的选择方法

为了匹配电源的物理特征和性能特征(如重量、体积、容量、电压和价格等)来满足给定任务 的要求,提出了一种电源的选择方法. 电源的物理特征和性能特征根据制造商的数据进行分 类整理,并且利用先进的选择软件建立了数据库,从而可以根据电压、最大电流、质量能量 密度、体积能量密度和价格来构建性能图,系统地比较不同种类的电源. 移动电话蓄电池选 择的具体案例研究表明,所提出的电源选择方法可以作为一种初步设计工具.     

A nonlocal species concentration theory for diffusion and phase changes in electrode particles of lithium ion batteries

A nonlocal species concentration theory for diffusion and phase changes is introduced from a nonlocal free energy density. It can be applied, say, to electrode materials of lithium ion batteries. This theory incorporates two second-order partial differential equations involving second-order spatial derivatives of species concentration and an additional variable called nonlocal species concentration. Nonlocal species concentration theory can be interpreted as an extension of the Cahn–Hilliard theory. In principle, nonlocal effects beyond an infinitesimal neighborhood are taken into account. In this theory, the nonlocal free energy density is split into the penalty energy density and the variance energy density. The thickness of the interface between two phases in phase segregated states of a material is controlled by a normalized penalty energy coefficient and a characteristic interface length scale. We implemented the theory in COMSOL Multiphysics\(^{\circledR }\) for a spherically symmetric boundary value problem of lithium insertion into a \(\hbox {Li}_x\hbox {Mn}_2\hbox {O}_4\) cathode material particle of a lithium ion battery. The two above-mentioned material parameters controlling the interface are determined for \(\hbox {Li}_x\hbox {Mn}_2\hbox {O}_4\), and the interface evolution is studied. Comparison to the Cahn–Hilliard theory shows that nonlocal species concentration theory is superior when simulating problems where the dimensions of the microstructure such as phase boundaries are of the same order of magnitude as the problem size. This is typically the case in nanosized particles of phase-separating electrode materials. For example, the nonlocality of nonlocal species concentration theory turns out to make the interface of the local concentration field thinner than in Cahn–Hilliard theory.     

Highly dispersed Mn2O3 microspheres: Facile solvothermal synthesis and their application as Li-ion battery anodes

Nanostructured transition metal oxides are promising alternative anodes for lithium ion batteries. Li-ion storage performance is expected to improve if high packing density energy particles are available. Herein, Mn₂O₃ microspheres with a ca. 18 μm diameter and a tapped density of 1.33 g/cm³ were synthesized by a facile solvothermal–thermal coversion route. Spherical MnCO₃ precursors were obtained through solvothermal treatment and they decomposed and converted into Mn₂O₃ microspheres at an annealing temperature of 700 °C. The Mn₂O₃ microspheres consisted of Mn₂O₃ nanoparticles with an average 40 nm diameter. These porous Mn₂O₃ microspheres allow good electrolyte penetration and provide an ion buffer reservoir to ensure a constant electrolyte supply. The Mn₂O₃ microspheres have reversible capacities of 590 and 320 mAh/g at 50 and 400 mA/g, respectively. We thus report an efficient route for the fabrication of energy particles for advanced energy storage.     

Utilizing the capacity below 0 V to maximize lithium storage of hard carbon anodes

Compared with conventional graphite anode, hard carbons have the potential to make reversible lithium storage below 0 V accessible due to the formation of dendrites is slow. However, under certain conditions of high currents and lithiation depths, the irreversible plated lithium occurs and then results in the capacity losses. Herein, we systematically explore the true reversibility of hard carbon anodes below 0 V. We identify the lithiation boundary parameters that control the reversible capacity of hard carbon anodes. When the boundary capacity is controlled below 400 mAh g⁻¹ with current density below 50 mA g⁻¹, no lithium dendrites are observed during the lithiation process. Compared with the discharge cut-off voltage to 0 V, this boundary provides a nearly twice reversible capacity with the capacity retention of 80% after 172 cycles. The results of characterization and finite element model reveal that the large reversible capacity below 0 V of hard carbon anodes is mainly benefited from the dual effect of lithium intercalation and reversible lithium film. After the lithium intercalation, the over-lithiation induces the quick growth of lithium dendrites, worsening the electrochemical irreversibility. This work enables insights of the potentially low-voltage performance of hard carbons in lithium-ion batteries.     

Thermoelastic stresses in SiC single crystals grown by the physical vapor transport method

A finite element-based thermoelastic anisotropic stress model for hexagonal silicon carbide polytype is developed for the calculation of thermal stresses in SiC crystals grown by the physical vapor transport method. The composite structure of the growing SiC crystal and graphite lid is considered in the model. The thermal expansion match between the crucible lid and SiC crystal is studied for the first time. The influence of thermal stress on the dislocation density and crystal quality is discussed. The project supported by the National Natural Science Foundation of China (10472126) and the Knowledge Innovation Program of Chinese Academy of Sciences. The English text was polished by Keren Wang     

Roles of metal element substitutions from the bimetallic solid state electrolytes in lithium batteries

All-solid-state lithium batteries (ASSLBs), receiving extensive attentions and studies, exhibit better safety, environmental friendliness, stability, wider electrochemical stability window and higher energy density than traditionally liquid lithium batteries. In a variety of inorganic materials, with highly replaceable, the non-lithium metal elements emerge in endlessly and affect performances in diversiform ways. Due to facile preparation, convertible structures and excellent properties, the lithium-containing bimetallic granular materials are often applied as important components of electrolytes in lithium batteries. In this review, in terms of the properties of substituted elements, changing crystal structures, increasing vacancies or defects and improving the interfacial conductions, the roles of metal element substitutions of inorganic particles on the improvement of solid-state electrolytes are expounded. And the applications of substituted strategies in ASSLBs as the host of inorganic particles electrolytes and as fillers or modifications for composite electrolytes are also investigated and discussed. It also summarizes the current concerns and obstacles that need to be broken through, as well as provides a basis guide for the selection and optimization of inorganic particles.     

Atomic-scale simulations for lithium dendrite growth driven by strain gradient

Dendrite formation is a major obstacle, e.g., capacity loss and short circuit, to the next-generation high-energy-density lithium (Li)-metal batteries. The development of successful Li dendrite mitigation strategies is impeded by an insufficient understanding in Li dendrite growth mechanisms. The Li-plating-induced internal stress in Li-metal and its effects on dendrite growth have been widely studied, but the underlying microcosmic mechanism is elusive. In the present study, the role of the plating-induced stress in dendrite formation is analyzed through first-principles calculations and ab initio molecular dynamic (AIMD) simulations. It is shown that the deposited Li forms a stable atomic nanofilm structure on the copper (Cu) substrate, and the adsorption energy of Li atoms increases from the Li-Cu interface to the deposited Li surface, leading to more aggregated Li atoms at the interface. Compared with the pristine Li-metal, the deposited Li in the early stage becomes compacted and suffers the in-plane compressive stress. Interestingly, there is a giant strain gradient distribution from the Li-Cu interface to the deposited Li surface, making the deposited atoms adjacent to the Cu surface tend to press upwards with perturbation and causing the dendrite growth. This provides an insight into the atomicscale origin of Li dendrite growth, and may be useful for suppressing the Li dendrite in Li-metal-based rechargeable batteries.     

Strong dependency of lithium diffusion on mechanical constraints in high-capacity Li-ion battery electrodes

The effect of external constraints on Li diffusion in high-capacity Li-ion battery electrodes is investigated us- ing a coupled finite deformation theory. It is found that thin- film electrodes on rigid substrates experience much slower diffusion rates compared with free-standing films with the same material properties and geometric dimensions. More importantly, the study reveals that mechanical driving forces tend to retard diffusion in highly-constrained thin films when lithiation-induced softening is considered, in contrast to the fact that mechanical driving forces always enhance diffusion when deformation is fully elastic. The results provide further proof that nano-particles are a better design option for next-generation alloy-based electrodes compared with thin films.     

Higher-order polysulfides induced thermal runaway for 1.0 Ah lithium sulfur pouch cells

Comprehensive analyses on thermal runaway mechanisms are critically vital to achieve the safe lithium–sulfur (Li–S) batteries. The reactions between dissolved higher-order polysulfides and Li metal were found to be the origins for the thermal runaway of 1.0 Ah cycled Li–S pouch cells. 16-cycle pouch cell indicates high safety, heating from 30 to 300 °C without thermal runaway, while 16-cycle pouch cell with additional electrolyte undergoes severe thermal runaway at 147.9 °C, demonstrating the key roles of the electrolyte on the thermal safety of batteries. On the contrary, thermal runaway does not occur for 45-cycle pouch cell despite the addition of the electrolyte. It is found that the higher-order polysulfides (Li₂S_x ≥ 6) are discovered in 16-cycle electrolyte while the sulfur species in 45-cycle electrolyte are Li₂S_x ≤ 4. In addition, strong exothermic reactions are discovered between cycled Li and dissolved higher-order polysulfide (Li₂S₆ and Li₂S₈) at 153.0 °C, driving the thermal runaway of cycled Li–S pouch cells. This work uncovers the potential safety risks of Li–S batteries and negative roles of the polysulfide shuttle for Li–S batteries from the safety view.     

Mesoporous composite of LiFePO4 and carbon microspheres as positive-electrode materials for lithium-ion batteries

Mesoporous LiFePO₄/C microspheres consisting of LiFePO₄ nanoparticles are successfully fabricated by an eco-friendly hydrothermal approach combined with high-temperature calcinations using cost-effective LiOH and Fe³⁺ salts as raw materials. In this strategy, pure mesoporous LiFePO₄ microspheres, which are composed of LiFePO₄ nanoparticles, were uniformly coated with carbon (∼1.5 nm). Benefiting from this unique architecture, these mesoporous LiFePO₄/C microspheres can be closely packed, having high tap density. The initial discharge capacity of LiFePO₄/C microspheres as positive-electrode materials for lithium-ion batteries could reach 165.3 mAh/g at 0.1 C rate, which is notably close to the theoretical capacity of LiFePO₄ due to the large BET surface area, which provides for a large electrochemically available surface for the active material and electrolyte. The material also exhibits high rate capability (∼100 mAh/g at 8 C) and good cycling stability (capacity retention of 92.2% after 400 cycles at 8 C rate).     

Ni-W-Co/SiC复合材料磨损特性与磨损机制

研究了ＳｉＣ颗粒和ＳｉＣ晶须为复合第二相的Ｎｉ－Ｗ－Ｃｏ合金基复合材料的磨损特性和磨损机制．结果表明,复合相含量、几何特性及载荷和滑动速度对复合材料的耐磨性影响很大．其原因在于ＳｉＣ颗粒与ＳｉＣ晶须以不同的形式发生流失．     

Numerical computation of central crack growth in an active particle of electrodes influenced by multiple factors

Mechanical degradation, especially fractures in active particles in an electrode, is a major reason why the capacity of lithium-ion batteries fades. This paper proposes a model that couples Li-ion diffusion, stress evolution, and damage mechanics to simulate the growth of central cracks in cathode particles \((\hbox {LiMn}_{2}\hbox {O}_{4})\) by an extended finite element method by considering the influence of multiple factors. The simulation shows that particles are likely to crack at a high discharge rate, when the particle radius is large, or when the initial central crack is longer. It also shows that the maximum principal tensile stress decreases and cracking becomes more difficult when the influence of crack surface diffusion is considered. The fracturing process occurs according to the following stages: no crack growth, stable crack growth, and unstable crack growth. Changing the charge/discharge strategy before unstable crack growth sets in is beneficial to prevent further capacity fading during electrochemical cycling.     

Composing atomic transition metal sites for high-performance bifunctional oxygen electrocatalysis in rechargeable zinc–air batteries

Rechargeable zinc–air batteries have attracted extensive attention as clean, safe, and high-efficient energy storage devices. However, the oxygen redox reactions at cathode are highly sluggish in kinetics and severely limit the actual battery performance. Atomic transition metal sites demonstrate high electrocatalytic activity towards respective oxygen reduction and evolution, while high bifunctional electrocatalytic activity is seldomly achieved. Herein a strategy of composing atomic transition metal sites is proposed to fabricate high active bifunctional oxygen electrocatalysts and high-performance rechargeable zinc–air batteries. Concretely, atomic Fe and Ni sites are composed based on their respective high electrocatalytic activity on oxygen reduction and evolution. The composite electrocatalyst demonstrates high bifunctional electrocatalytic activity (ΔE = 0.72 V) and exceeds noble-metal-based Pt/C + Ir/C (ΔE = 0.79 V). Accordingly, rechargeable zinc–air batteries with the composite electrocatalyst realize over 100 stable cycles at 25 mA cm⁻². This work affords an effective strategy to fabricate bifunctional oxygen electrocatalysts for high-performance rechargeable zinc–air batteries.