An Ultra‐Long‐Life Lithium‐Rich Li1.2Mn0.6Ni0.2O2 Cathode by Three‐in‐One Surface Modification for Lithium‐Ion Batteries

Voltage decay and capacity fading are the main challenges for the commercialization of Li‐rich Mn‐based layered oxides (LLOs). Now, a three‐in‐one surface treatment is designed via the pyrolysis of urea to improve the voltage and capacity stability of Li_1.2Mn_0.6Ni_0.2O₂ (LMNO), by which oxygen vacancies, spinel phase integration, and N‐doped carbon nanolayers are synchronously built on the surface of LMNO microspheres. Oxygen vacancies and spinel phase integration suppress irreversible O₂ release and help lithium ion diffusion, while N‐doped carbon nanolayer mitigates the corrosion of electrolyte with excellent conductivity. The electrochemical performance of LMNO after the treatment improves significantly; the capacity retention rate after 500 cycles at 1 C is still as high as 89.9 % with a very small voltage fading rate of 1.09 mV cycle^?1. This three‐in‐one surface treatment strategy can suppress the voltage decay and capacity fading of LLOs.     

Liquid‐Free Lithium–Oxygen Batteries

Non‐aqueous lithium–oxygen batteries are considered as most advanced power sources, albeit they are facing numerous challenges concerning almost each cell component. Herein, we diverge from the conventional and traditional liquid‐based non‐aqueous Li–O₂ batteries to a Li–O₂ system based on a solid polymer electrolyte (SPE‐) and operated at a temperature higher than the melting point of the polymer electrolyte, where useful and most applicable conductivity values are easily achieved. The proposed SPE‐based Li‐O₂ cell is compared to Li–O₂ cells based on ethylene glycol dimethyl ether (glyme) through potentiodynamic and galvanostatic studies, showing a higher cell discharge voltage by 80 mV and most significantly, a charge voltage lower by 400 mV. The solid‐state battery demonstrated a comparable discharge‐specific capacity to glyme‐based Li–O₂ cells when discharged at the same current density. The results shown here demonstrate that the safer PEO‐based Li–O₂ battery is highly advantageous and can potentially replace the contingent of liquid‐based cells upon further investigation.     

Boosting Li-ion storage in Li2MnO3 by unequal-valent Ti4+-substitution and interlayer Li vacancies building

Lithium rich layered oxide (LRLO) has been considered as one of the promising cathodes for lithium-ion batteries (LIBs). The high voltage and large capacity of LRLO depend on Li₂MnO₃ phase. To ameliorate the electrochemical performance of Li₂MnO₃, also written as Li(Li_1/3Mn_2/3)O₂, we propose a strategy to substitute Mn⁴⁺ and Li⁺ in Mn/Li transition metal layer with Ti⁴⁺, which can stabilize the structure of Li₂MnO₃ by inhibiting the excessive oxidation of O^2? above 4.5 V. More significantly, the unequal-valent substitution brings about the emergence of interlayer Li vacancies, which can promote the Li-ion diffusion based on the enlarged interlayer and increase the capacity by activating the Mn^3+/4+ redox. We designed Li_0.7[Li_1/3Mn_2/3]_0.7Ti_0.3O₂ with high interlayer Li vacancies, which presents a high capacity (290 mAh/g at 10 mA/g) and stable cycling performance (84% over 60 cycles at 50 mA/g). We predict that this strategy will be helpful to further improve the electrochemical performance of LRLOs.     

An Ultra-Long-Life Lithium-Rich Li1.2Mn0.6Ni0.2O2 Cathode by Three-in-One Surface Modification for Lithium-Ion Batteries

Voltage decay and capacity fading are the main challenges for the commercialization of Li-rich Mn-based layered oxides (LLOs). Now, a three-in-one surface treatment is designed via the pyrolysis of urea to improve the voltage and capacity stability of Li_1.2Mn_0.6Ni_0.2O₂ (LMNO), by which oxygen vacancies, spinel phase integration, and N-doped carbon nanolayers are synchronously built on the surface of LMNO microspheres. Oxygen vacancies and spinel phase integration suppress irreversible O₂ release and help lithium ion diffusion, while N-doped carbon nanolayer mitigates the corrosion of electrolyte with excellent conductivity. The electrochemical performance of LMNO after the treatment improves significantly; the capacity retention rate after 500 cycles at 1 C is still as high as 89.9 % with a very small voltage fading rate of 1.09 mV cycle⁻¹. This three-in-one surface treatment strategy can suppress the voltage decay and capacity fading of LLOs.     

溶胶-凝胶法合成Li_(1-x)Na_xMn_2O_4及其作为水系锂离子电池正极材料的电化学性能

用溶胶凝胶法合成了Na+离子掺杂的Li_(1-x)Na_xMn_2O_4(x=0,0.01,0.03,0.05)。X射线衍射图表明Na+取代Li+进入Li_(1-x)Na_xMn_2O_4晶格中,扫描电镜图看出产物是粒径为100~300 nm的颗粒。恒流充放电测试结果表明,Li_(0.97)Na_(0.03)Mn_2O_4在2C倍率下循环100圈后放电容量保持率比未掺杂的LiMn_2O_4从51.2%提升到84.1%。循环伏安测试表明Na+离子掺杂降低了材料极化且增大了锂离子扩散系数。10C倍率下Li0.97Na0.03Mn2O4仍有79.0 m Ah·g-1的放电容量,高于未掺杂样品的52.1 m Ah·g~(-1)。Na+离子掺杂可以稳定材料结构并提高锂离子扩散系数,从而提高LiMn_2O_4的电化学性能,是一种可行的改性方法。     

溶胶-凝胶法合成Li1-xNaxMn2O4及其作为水系锂离子电池正极材料的电化学性能

用溶胶凝胶法合成了Na⁺离子掺杂的Li_1-xNa_xMn₂O₄(x=0,0.01,0.03,0.05)。X射线衍射图表明Na⁺取代Li⁺进入Li_1-xNa_x Mn₂O₄晶格中,扫描电镜图看出产物是粒径为100~300 nm的颗粒。恒流充放电测试结果表明,Li_0.97Na_0.03Mn₂O₄在2C倍率下循环100圈后放电容量保持率比未掺杂的LiMn₂O₄从51.2%提升到84.1%。循环伏安测试表明Na⁺离子掺杂降低了材料极化且增大了锂离子扩散系数。10C倍率下Li_0.97Na_0.03Mn₂O₄仍有79.0 mAh·g^-1的放电容量,高于未掺杂样品的52.1 mAh·g^-1。Na⁺离子掺杂可以稳定材料结构并提高锂离子扩散系数,从而提高LiMn₂O₄的电化学性能,是一种可行的改性方法。     

Superoxide Stabilization and a Universal KO2 Growth Mechanism in Potassium–Oxygen Batteries

Rechargeable potassium–oxygen (K‐O₂) batteries promise to provide higher round‐trip efficiency and cycle life than other alkali–oxygen batteries with satisfactory gravimetric energy density (935 Wh kg^?1). Exploiting a strong electron‐donating solvent, for example, dimethyl sulfoxide (DMSO) strongly stabilizes the discharge product (KO₂), resulting in significant improvement in electrode kinetics and chemical/electrochemical reversibility. The first DMSO‐based K‐O₂ battery demonstrates a much higher energy efficiency and stability than the glyme‐based electrolyte. A universal KO₂ growth model is developed and it is demonstrated that the ideal solvent for K‐O₂ batteries should strongly stabilize superoxide (strong donor ability) to obtain high electrode kinetics and reversibility while providing fast oxygen diffusion to achieve high discharge capacity. This work elucidates key electrolyte properties that control the efficiency and reversibility of K‐O₂ batteries.     

Cycling performance of LiNi<Subscript><Emphasis Type="Italic">y</Emphasis></Subscript>Mn<Subscript>2 − <Emphasis Type="Italic">y</Emphasis></Subscript>O<Subscript>4</Subscript> prepared by the solid-state reaction

In order to improve the cycling performance of LiMn₂O₄, a part of Mn in LiMn₂O₄ was replaced by Ni. LiNi _y Mn_{2 − y} O₄ (y = 0.02, 0.05, 0.10, 0.15, and 0.20) were synthesized by preheating a mixture of LiOH, MnO₂ (CMD), and NiO at 400°C for 10 h and then calcining at 850°C for 48 h in air with intermediate grinding. The voltage vs. discharge capacity curves at a current density of 300 μA/cm² between 3.5 and 4.3 V showed two plateaus, but the plateaus became unclear as the value of y increased. The sample with y = 0.02 had the largest first discharge capacity of 118.1 mA h/g. The LiNi_0.10Mn_1.90O₄ sample had a relatively large first discharge capacity of 95.0 mA h/g and snowed an excellent cycling performance.     

Effects of alloying elements and binder on the electrochemical behavior of metal hydride electrodes in potassium hydroxide electrolyte

This investigation examines the effect of alloying elements on the charge–discharge performance of LaNi_3.6(Co+Mn+Al)_1.4 electrodes in 7 M KOH electrolyte. The activation behavior and the effect of binder content were also examined. Both half-cell and full-cell systems were employed to evaluate the electrochemical performance. Experimental results indicated that a few cycles of charge–discharge at a rate of 150 mA/g in 7 M KOH electrolyte were sufficient to activate the freshly prepared LaNi_3.6(Co+Mn+Al)_1.4 electrodes. The amount of binder affected the activation behavior, the overvoltage for hydrogen ions reduction and the discharge capacity of the MmNi_3.55Co_0.75Mn_0.4Al_0.3 electrode. In the alloy of the LaNi_3.6(Co+Mn+Al)_1.4 electrodes, a high Co content helped to promote both the capacity at a relatively low discharging rate and the cyclic life. An increase of the Al content raised the discharge voltage and improved the high rate discharge capacity, but reduced the cyclic stability. The alloy with a high Mn content required the least cathodic polarization during charging but had the lowest discharge capacity at a rather high discharging rate.     

High capacity lithium-manganese-nickel-oxide composite cathodes with low irreversible capacity loss and good cycle life for lithium ion batteries

We report a method to eliminate the irreversible capacity of 0.4Li_2MnO_3·0.6LiNi_(0.5)Mn_(0.5)O_2(Li_(1.17)Ni_(0.25)Mn_(0.583)O_2) by decreasing lithium content to yield integrated layered-spinel structures.XRD patterns,High-resolution TEM image and electrochemical cycling of the materials in lithium cells revealed features consistent with the presence of spinel phase within the materials.When discharged to about 2.8 V,the spinel phase of LiM_2O_4(M=Ni,Mn) can transform to rock-salt phase of Li_2M_2O_4(M=Ni,Mn) during which the tetravalent manganese ions are reduced to an oxidation state of 3.0.So the spinel phase can act as a host to insert back the extracted lithium ions(from the layered matrix) that could not embed back into the layered lattice to eliminate the irreversible capacity loss and increase the discharge capacity.Their electrochemical properties at room temperature showed a high capacity(about 275 mAh g~(-1) at 0.1 C) and exhibited good cycling performance.     

PO43-掺杂和AlF3包覆协同增强Li1.2Ni0.13Co0.13Mn0.54O2正极材料电化学性能

本研究采用PO₄^3-掺杂和AlF₃包覆的协同改性策略制备了P-LNCM@AlF₃正极材料(P=PO₄^3-,LNCM=Li_1.2Ni_0.13Co_0.13Mn_0.54O₂),提高了LNCM的结构稳定性以及抑制了界面副反应。其中,大四面体的PO₄^3-聚阴离子掺杂在晶格中抑制了过渡金属离子的迁移,降低体积变化,从而稳定了晶体结构,而且PO₄^3-掺杂能够扩大锂层间距,促进Li⁺的扩散,从而提升材料的倍率性能。此外,AlF₃包覆层能抑制材料与电解液的副反应从而提升界面稳定性。基于以上优势,P-LNCM@AlF₃正极表现出了优异的电化学性能。在1C电流密度下表现出了179.2 mAh·g^-1     

Stabilizing Cobalt-free Li-rich Layered Oxide Cathodes through Oxygen Lattice Regulation by Two-phase Ru Doping

The application of Li-rich layered oxides is hindered by their dramatic capacity and voltage decay on cycling. This work comprehensively studies the mechanistic behaviour of cobalt-free Li_1.2Ni_0.2Mn_0.6O₂ and demonstrates the positive impact of two-phase Ru doping. A mechanistic transition from the monoclinic to the hexagonal behaviour is found for the structural evolution of Li_1.2Ni_0.2Mn_0.6O_2, and the improvement mechanism of Ru doping is understood using the combination of in operando and post-mortem synchrotron analyses. The two-phase Ru doping improves the structural reversibility in the first cycle and restrains structural degradation during cycling by stabilizing oxygen (O²⁻) redox and reducing Mn reduction, thus enabling high structural stability, an extraordinarily stable voltage (decay rate <0.45 mV per cycle), and a high capacity-retention rate during long-term cycling. The understanding of the structure-function relationship of Li_1.2Ni_0.2Mn_0.6O₂ sheds light on the selective doping strategy and rational materials design for better-performance Li-rich layered oxides.     

Influence of the technical process parameters on structural,mechanical and electrochemical properties of LiNi0.8Co0.15Al0.05O2 based electrodes – A review

The electrode manufacturing for lithium-ion batteries has been systematically evaluated. It has been shown that a proper tailoring of the electrodes can greatly improve both the electrochemical performance and the energy density of the battery. The pre-treatment of the electrode components, the degree of the electrode compacting and the mixing process have proven to have a strong impact on the electrochemical performance of the composite electrodes based on LiNi_0.80Co_0.15Al_0.05O₂. In addition, blending LiNi_0.80Co_0.15Al_0.05O₂ – NCA with lithium manganese oxide spinel (LiMn₂O₄, LMS) has exhibited beneficial effects on the discharge capacity of the blends, thus on the energy density and in the same time decreases the Mn dissolution from spinel structure. Moreover, the detailed study of the storage behaviour of LMS/NCA blend reveals that dissolved Mn from spinel structure is re-precipitable on NCA particles and so that less Mn²⁺ ions will be available in the electrolyte, which can migrate to the anode graphite and deposit thereof.     

锂离子电池镍掺杂尖晶石LiMn2O4正极材料的电子结构

采用密度泛甬平面波赝势方法对LiMn2O4和LiNi0.5Mn1.5O4的几何结构进行了优化,并计算了相应的电子结构.计算的结果表明:在Li 脱嵌前后,LiMn2O4和LiNi0.5Mn1.5O4均为导体,且锂元素主要以离子形式存在于两种材料中,O2p轨道与Mn(Ni)的3d轨道形成了较强的共价键.Li 嵌入导致Mn(Ni)3d轨道的态密度峰发生移动.Ni的掺杂导致Mn(Ni)和O2p轨道的成键作用得以加强,电子在Mn(Ni)3d轨道的填充发生变化,从而提高了电池的充放电电压.     

PO43-掺杂和AlF3包覆协同增强Li1.2Ni0.13Co0.13Mn0.54O2正极材料电化学性能

本研究采用PO₄^3-掺杂和AlF₃包覆的协同改性策略制备了P-LNCM@AlF₃正极材料(P=PO₄^3- ,LNCM=Li_1.2Ni_0.13Co_0.13Mn_0.54O₂),提高了LNCM的结构稳定性以及抑制了界面副反应。其中,大四面体的PO₄^3-聚阴离子掺杂在晶格中抑制了过渡金属离子的迁移,降低体积变化,从而稳定了晶体结构,而且PO₄^3-掺杂能够扩大锂层间距,促进Li⁺的扩散,从而提升材料的倍率性能。此外,AlF₃包覆层能抑制材料与电解液的副反应从而提升界面稳定性。基于以上优势,P-LNCM@AlF₃正极表现出了优异的电化学性能。在1C电流密度下表现出了179.2 mAh·g^-1的放电比容量,循环200圈后仍有161.5 mAh·g^-1的放电比容量,容量保持率可达90.12%。即使在5C的高电流密度下仍可提供128.8 mAh·g^-1的放电比容量。     

Remarkable improvement of cyclic stability in Li–O2 batteries using ruthenocene as a redox mediator

Nonaqueous Li–O₂ batteries attract attention for their theoretical specific energy density. However, due to the difficulty of decomposition of Li₂O₂, Li–O₂ batteries have high charge overpotential and poor cycling life. So all kinds of catalysts have been studied on the cathode. Compared to heterogeneous solid catalysts, soluble catalysts achieve faster and more effective transport of electrons by reversible redox pairs. Here, we first report ruthenocene (Ruc) as a mobile redox mediator in a Li–O₂ battery. 0.01 mol/L Ruc in the electrolyte effectively reduces the charging voltage by 610 mV. Additionally, Ruc greatly increases the cycling life by four-fold (up to 83 cycles) with a simple ketjen black (KB) cathode. The results of SEM, XPS and XRD confirm that less discharge product residue accumulated after recharge. To verify the reaction mechanisms of the mediator, free energy profiles of the possible reaction pathways based on DFT are provided.     

Development of a new in situ cell for the X–ray Absorption Fine Structure analysis of the electrochemical reaction in a rechargeable battery and its application to the Lithium Battery Material,Li1+yMn2−yO4

An electrochemical cell was developed for the in situ transmission X–ray Absorption Fine Structure measurements of the charge/discharge process of the cathode materials of lithium secondary batteries, from which Li can be electrochemically deintercalated or intercalated. The dynamical structural behavior of Mn in Li(Mn_1.93Li_0.07)O₄, and Li(Mn_1.85Li_0.15)O₄ as a function of both excess Li content and the Li deintercalation was revealed using the in situ cell. The analysis disclosed the coexistence of two MnO₆–coordination polyhedra with different Mn–O distances for the Mn³⁺ and Mn⁴⁺ ions at the 16d site of the spinel structure. Because the charge–discharge process accompanies the oxidation–reduction of the Mn ions, this size difference causes an unfavorable lattice distortion for the electrode materials which can cause a loss of cell capacity after cyclic use of the cell. A partial substitution of Li for Mn will diminish this effect and will be favorable for the battery material.     

Effects of Al-doping on the stabilization of monoclinic LiMnO2

Electronic structures of monoclinic LiMnO₂ and LiMn_0.9375Al_0.0625O₂ with ferromagnetic (FM) and antiferromagnetic (AF) ordering have been investigated by ab initio calculation within spin-polarized generalized gradient approximation method. An Al-doping induced complicated AF configuration has been calculated to be the ground state, which suggests a robust Al-doping effect on the magnetic and electronic structures of the monoclinic LiMnO₂. The calculated Mulliken population analyses and partial density of states of Mn-3d and O-2p reveal that a single Al dopant stabilizes its six nearest-neighbor Mn ions in their respective octahedral sites, thereby hindering the migration of Mn ions into the interlayer Li sites during the Li intercalation-deintercalation and therefore improving both the structural stability and the electrochemical performance of the material. Additionally, it is found out that the Al-doping can decrease the JT effect and increase the intercalation voltage. The Al-doping-induced negative formation energy indicates that 6.25% Mn ions in monoclinic LiMnO₂ can be substituted stably by Al ions, to which the equilibrium but not metastable phase of monoclinic LiMn_0.9375Al_0.0625O₂ can be attributed.     

New Reaction Pathway of Superoxide Disproportionation Induced by a Soluble Catalyst in Li-O2 Batteries

Aprotic Li-O₂ battery has attracted considerable interest for high theoretical energy density, however the disproportionation of the intermediate of superoxide (O₂⁻) during discharge and charge leads to slow reaction kinetics and large voltage hysteresis. Herein, the chemically stable ruthenium tris(bipyridine) (RB) cations are employed as a soluble catalyst to alternate the pathway of O₂⁻ disproportionation and its kinetics in both the discharge and charge processes. RB captures O₂⁻ dimer and promotes their intramolecular charge transfer, and it decreases the energy barrier of the disproportionation reaction from 7.70 to 0.70 kcal mol⁻¹. This facilitates the discharge and charge processes and simultaneously mitigates O₂⁻ and singlet oxygen related side reactions. These endow the Li-O₂ battery with reduced discharge/charge voltage gap of 0.72 V and prolonged lifespan for over 230 cycles when coupled with RuO₂ catalyst. This work highlights the vital role of superoxide disproportionation for Li-O₂ battery.     

Photo‐energy Conversion and Storage in an Aprotic Li‐O2 Battery

A photo‐involved Li‐O₂ battery with carbon nitride (C₃N₄) is presented as a bifunctional photocatalyst to accelerate both oxygen reduction and evolution reactions. With illumination in a discharge process, photoelectrons generated in the conduction band (CB) of C₃N₄ are donated to O₂ for O₂^?, which undergoes a second electron reduction to O₂^2? and gives the final product of Li₂O₂; in a reverse process, holes left behind in the valence band (VB) of C₃N₄ plus an applied lower voltage than the equilibrium drive the Li₂O₂ oxidation. The discharge voltage is significantly increased to 3.22 V, surpassing the thermodynamic limit of 2.96 V, and the charge voltage is reduced to 3.38 V. This leads to a record‐high round‐trip efficiency of 95.3 % and energy density increase of 23.0 % compared to that in the dark.