The role of Li2MO2 structures (M=metal ion) in the electrochemistry of (x)LiMn0.5Ni0.5O2·(1−x)Li2TiO3 electrodes for lithium-ion batteries

The electrochemical reactions of lithium with layered composite electrodes (x)LiMn_0.5Ni_0.5O₂·(1−x)Li₂TiO₃ were investigated at low voltages. The metal oxide 0.95LiMn_0.5Ni_0.5O₂·0.05Li₂TiO₃ (x=0.95) which can also be represented in layered notation as Li(Mn_0.46Ni_0.46Ti_0.05Li_0.02)O₂, can react with one equivalent of lithium during an initial discharge from 3.2 to 1.4 V vs. Li⁰. The electrochemical reaction, which corresponds to a theoretical capacity of 286 mAh/g, is hypothesized to form Li₂(Mn_0.46Ni_0.46Ti_0.05Li_0.02)O₂ that is isostructural with Li₂MnO₂ and Li₂NiO₂. Similar low-voltage electrochemical behavior is also observed with unsubstituted, standard LiMn_0.5Ni_0.5O₂ electrodes (x=1). In situ X-ray absorption spectroscopy (XAS) data of Li(Mn_0.46Ni_0.46Ti_0.05Li_0.02)O₂ electrodes indicate that the low-voltage (<1.8 V) reaction is associated primarily with the reduction of Mn⁴⁺ to Mn²⁺. Symmetric rocking-chair cells with the configuration Li(Mn_0.46Ni_0.46Ti_0.05Li_0.02)O₂/Li(Mn_0.46Ni_0.46Ti_0.05Li_0.02)O₂ were tested. These electrodes provide a rechargeable capacity in excess of 300 mAh/g when charged and discharged over a 3.3 to −3.3 V range and show an insignificant capacity loss on the initial cycle. These findings have implications for combating the capacity-loss effects at graphite, metal–alloy, or intermetallic negative electrodes against lithium metal-oxide positive electrodes of conventional lithium-ion cells.     

Comparison of the chemical stability of the high energy density cathodes of lithium-ion batteries

With an objective to assess the chemical stabilities and their consequences in cell performance, the variations of oxygen content with lithium content (1−x) in chemically delithiated Li_1−xCoO₂, Li_1−xNi_0.85Co_0.15O₂, and Li_1−xMn₂O₄ cathodes have been monitored with redox titrations. The Li_1−xCoO₂ system tends to lose oxygen from the lattice at deep lithium extraction, while the Li_1−xNi_0.85Co_0.15O₂ system does not lose oxygen at least for (1−x)>0.3. The chemical instability with a tendency to lose oxygen at deep lithium extraction could be the reason for the limited practical capacity of the Li_1−xCoO₂ system (140 mA h/g) compared to that realized with the Li_1−xNi_0.85Co_0.15O₂ system (180 mA h/g). The Li_1−xMn₂O₄ spinel maintains an oxygen content of 4.0 without losing any oxygen for 0.15⩽(1−x)⩽1.     

Layered xLiMO2·(1−x)Li2M′O3 electrodes for lithium batteries: a study of 0.95LiMn0.5Ni0.5O2·0.05Li2TiO3

The electrochemical properties of 0.95LiMn_0.5Ni_0.5O₂·0.05Li₂TiO₃ have been investigated as part of a study of xLiMO₂·(1−x)Li₂M^′O₃ electrode systems for lithium batteries in which M=Co, Ni, Mn and M^′=Ti, Zr, Mn. The data indicate that the electrochemically inactive Li₂TiO₃ component contributes to the stabilization of LiMn_0.5Ni_0.5O₂ electrodes, which improves the coulombic efficiency of Li/xLiMn_0.5Ni_0.5O₂·(1−x)Li₂TiO₃ cells for x<1. The 0.95LiMn_0.5Ni_0.5O₂·0.05Li₂TiO₃ electrodes provide a rechargeable capacity of approximately 175 mAh/g at 50 °C when cycled between 4.6 and 2.5 V; there is no indication of spinel formation during electrochemical cycling.     

High capacity Li[Li0.2Mn0.54Ni0.13Co0.13]O2–V2O5 composite cathodes with low irreversible capacity loss for lithium ion batteries

With an aim to suppress the huge irreversible capacity loss encountered in high capacity layered oxide solid solutions between Li₂MnO₃ and LiMO₂ (M = Mn, Ni, and Co), layered Li[Li_0.2Mn_0.54Ni_0.13Co_0.13]O₂–V₂O₅ composite cathodes with various V₂O₅ contents have been investigated. The irreversible capacity loss decreases from 68 mAh/g at 100% Li[Li_0.2Mn_0.54Ni_0.13Co_0.13]O₂ to 0 mAh/g around 89 wt.% Li[Li_0.2Mn_0.54Ni_0.13Co_0.13]O₂–11 wt.% V₂O₅ as the lithium-free V₂O₅ serves as an insertion host to accommodate the lithium ions that could not be inserted back into the layered lattice after the first charge. The Li[Li_0.2Mn_0.54Ni_0.13Co_0.13]O₂–V₂O₅ composite cathodes with about 10–12 wt.% V₂O₅ exhibit an attractive discharge capacity of close to 300 mAh/g with little irreversible capacity loss and good cyclability.     

Sn-doped Li<Subscript>1.2</Subscript>Mn<Subscript>0.54</Subscript>Ni<Subscript>0.13</Subscript>Co<Subscript>0.13</Subscript>O<Subscript>2</Subscript> cathode materials for lithium-ion batteries with enhanced electrochemical performance

Sn-doped Li-rich layered oxides of Li_1.2Mn_0.54-x Ni_0.13Co_0.13Sn _x O₂ have been synthesized via a sol-gel method, and their microstructure and electrochemical performance have been studied. The addition of Sn⁴⁺ ions has no distinct influence on the crystal structure of the materials. After doped with an appropriate amount of Sn⁴⁺, the electrochemical performance of Li_1.2Mn_0.54-x Ni_0.13Co_0.13Sn _x O₂ cathode materials is significantly enhanced. The optimal electrochemical performance is obtained at x = 0.01. The Li_1.2Mn_0.53Ni_0.13Co_0.13Sn_0.01O₂ electrode delivers a high initial discharge capacity of 268.9 mAh g^?1 with an initial coulombic efficiency of 76.5% and a reversible capacity of 199.8 mAh g^?1 at 0.1 C with capacity retention of 75.2% after 100 cycles. In addition, the Li_1.2Mn_0.53Ni_0.13Co_0.13Sn_0.01O₂ electrode exhibits the superior rate capability with discharge capacities of 239.8, 198.6, 164.4, 133.4, and 88.8 mAh g^?1 at 0.2, 0.5, 1, 2, and 5 C, respectively, which are much higher than those of Li_1.2Mn_0.54Ni_0.13Co_0.13O₂ (196.2, 153.5, 117.5, 92.7, and 43.8 mAh g^?1 at 0.2, 0.5, 1, 2, and 5 C, respectively). The substitution of Sn⁴⁺ for Mn⁴⁺ enlarges the Li⁺ diffusion channels due to its larger ionic radius compared to Mn⁴⁺ and enhances the structural stability of Li-rich oxides, leading to the improved electrochemical performance in the Sn-doped Li_1.2Mn_0.54Ni_0.13Co_0.13O₂ cathode materials.     

A soft chemistry synthetic method for preparing LiNi0.8Co0.2O2 with enhanced electrochemical performances

Polycrystalline LiNi_0.8Co_0.2O₂ powders were synthesized via the citric acid-assisted liquid phase evaporation method. The precursors are homogenously mixed in the solutions at an atomic scale which is also reflected by the particle distribution of the final products. The optimal synthesis temperature is located at 750?°C where the particle size, crystalline structure, and the cation disorder between Li⁺ and Ni²⁺ ions have been balanced. A high discharge capacity of 191?mAh?g^?? (3.0??.3?V at 30?mA/g) is achieved in the first cycle for the 750?°C-prepared sample with a capacity retention of 89.37% after 96 cycles. Cyclic voltammetry and the differential capacity curves also reveal a moderate stable crystal structure of 750?°C-prepared LiNi_0.8Co_0.2O₂ during the prolonged cycles.     

Partially substituted lithium manganese oxides as 3 V cathode materials for secondary lithium batteries

Low temperature synthesis and electrochemical properties of partially substituted lithium manganese oxides are reported. We demonstrate various metallic cations (Cu²⁺, Ni²⁺, Fe³⁺, Co³⁺) can be incorporated in the 3 V layered cathodic material Li_0.45MnO_2.1. New compounds Li_0.45Mn_0.88Fe_0.12O_2.1, Li_0.45Mn_0.84Ni_0.16O_2.05, Li_0.45Mn_0.79Cu_0.21O_2.3, Li_0.45Mn_0.85Co_0.15O_2.3 are prepared. These 3 V cathode materials are characterized by the same shape of discharge-charge profiles but different values of the specific capacity, between 90 mAh g⁻¹ and 180 mAh g⁻¹. The best results in terms of capacity and cycle life are obtained with the selected content of 0.15 Co per mole of oxide, as the optimum composition. The high kinetics of Li⁺ transport in Li_0.45Mn_0.85Co_0.15O_2.3 compared to that in the Co-free material is consistent with a substitution of Mn(III) by Co(III) in MnO₂ sheets.     

Ag/C包覆对Li[Li0.2Mn0.54Ni0.13Co0.13]O2电化学性能的影响

运用共沉淀和元素化学沉积相结合的方法,制备出了具有Ag/C 包覆层的层状富锂固溶体材料Li[Li_0.2Mn_0.54Ni_0.13Co_0.13]O₂. 通过X 射线衍射（XRD）、场发射扫描电子显微镜（SEM）、透射电子显微镜（TEM）、恒流充放电、循环伏安（CV）,电化学阻抗谱（EIS）和X 射线能量散射谱（EDS）方法,研究了Ag/C 包覆层对Li[Li_0.2Mn_0.54Ni_0.13Co_0.13]O₂电化学性能的影响. 结果表明,Ag/C 包覆层的厚度约为25 nm,Ag/C 包覆在保持了固溶体材料α-NaFeO₂ 六方层状晶体结构的前提下,显著地改善了Li[Li_0.2Mn_0.54Ni_0.13Co_0.13]O₂ 的电化学性能. 在2.0-4.8 V（vs Li/Li⁺）的电压范围内,首次放电（0.05C）容量由242.6 mAh·g^-1提高到272.4 mAh·g^-1,库仑效率由67.6%升高到77.4%;在0.2C倍率下,30 次循环后,Ag/C 包覆的电极材料容量为222.6 mAh·g^-1,比未包覆电极材料的容量高出14.45%;包覆后的电极材料在1C下的容量仍为0.05C下的81.3%. 循环伏安及电化学交流阻抗谱研究表明,Ag/C包覆层抑制了材料在充放电过程中氧的损失,有效降低了Li[Li_0.2Mn_0.54Ni_0.13Co_0.13]O₂颗粒的界面膜电阻与电化学反应电阻.     

Comparison of the electrochemical properties of metallic layered nitrides containing cobalt,nickel and copper in the 1 V–0.02 V potential range

We report the first example of an intercalation compound based on the nitrogen framework in which lithium can be intercalated and deintercalated. A comparison of the structural and electrochemical properties of the ternary lithium cobalt, nickel and copper nitrides is performed. Vacancy layered structures of ternary lithium nitridocobaltates Li_3−2xCo_xN and nitridonickelates Li_3−2xNi_xN with 0.10 ⩽ x ⩽ 0.44 and 0.20 ⩽ x ⩽ 0.60, respectively, are proved to reversibly intercalate Li ions in the 1 V–0.02 V potential range. These host lattices can accommodate up to 0.35 Li ion par mole of nitride. Results herein obtained support Li insertion in vacancies located in Li₂N⁻ layers while interlayer divalent cobalt and nickel cations are reduced to monovalent species. No structural strain is induced by the insertion–extraction electrochemical reaction which explains the high stability of the capacity in both cases. For the Li_1.86Ni_0.57N compound, a stable faradaic yield of 0.30 F/mol, i.e. 130 mAh/g, is maintained at least for 100 cycles. Conversely, the ternary copper nitrides corresponding to the chemical composition Li_3−xCu_xN with 0.10 ⩽ x ⩽ 0.40 do not allow the insertion reaction to take place due to the presence of monovalent copper combined with the lack of vacancies to accommodate Li ions. In the latter case, the discharge of the lithium copper nitrides is not reversible.     

Synthesis and electrochemical properties of Li-rich Li[Ni<Subscript>0.5</Subscript>Co<Subscript>0.2</Subscript>Mn<Subscript>0.3</Subscript>]O<Subscript>2</Subscript> for pouch-typed cell

Layered transition metal oxide LiNi _x Co _y MnzO₂ cathode materials with different Li amount were successfully synthesized via co-precipitation method. Monodispersed Li[Ni_0.5Co_0.2Mn_0.3]O₂ and Li-rich Li_1.1[Ni_0.5Co_0.2Mn_0.3]O₂ spherical agglomeration consisted of secondary particles, which is favorable for the higher tap-density of materials, can be easily obtained. The pouch-typed cells with obtained materials were assembled to investigate electrochemical performance at level of full-cell. The results show that the assembled pouch-typed full-cells with Li-rich sample present higher capacity, better rate capability and cycle life.     

Comparison of the Chemical Stability of Li1−xCoO2 and Li1−xNi0.85Co0.15O2 Cathodes

The chemical stability of the layered Li_1−xCoO₂ and Li_1−xNi_0.85Co_O.15O₂ cathodes is compared by monitoring the oxygen content with lithium content (1−x) in chemically delithiated samples. The Li_1−xCoO₂ system tends to lose oxygen from the lattice at deep lithium extraction while the Li_1−xNi_0.85Co_0.15O₂ system does not lose oxygen at least for (1−x)>0.3. This difference seems to result in a lower reversible (practical) capacity (140 mA h/g) for LiCoO₂ compared to that for LiNi_0.85Co_0.15O₂ (180 Ma h/g). The loss of significant amount of oxygen leads to a sliding of oxide layers and the formation of a major P3 and a minor O1 phase for the end member CoO_2−δ with δ=0.33. In contrast, Ni_0.85Co_0.15O_2−δ with a small amount of δ=0.1 maintains the initial O3 layer structure.     

Comparison of corn starch-assisted sol–gel and combustion methods to prepare LiMn x Co y Ni z O2 compounds

In a novel attempt to exploit corn starch as gelling agent (in sol–gel method) and combustible fuel (in solution-assisted combustion method), high-capacity LiMn_0.4Ni_0.4Co_0.2O₂ and LiMn_1/3Ni_1/3Co_1/3O₂ cathode materials have been prepared and a comparison of electrochemical performance of the same has been made. Among the two compounds chosen for the study, LiMn_1/3Ni_1/3Co_1/3O₂ exhibits better physical and electrochemical properties. Particularly, LiMn_1/3Ni_1/3Co_1/3O₂ cathode synthesized using corn starch-assisted combustion method exhibits an appreciable capacity of 176 mAh g^?1, excellent capacity retention of 93 % up to 100 cycles and susceptible to rate capability test up to 1 C rate, thus qualifying the same for high-capacity and high-rate lithium battery applications. The study demonstrates the possibility of exploiting corn starch as gelling agent and as a combustible fuel in synthesizing lithium intercalating oxide compounds with improved electrochemical behaviour.     

碳酸盐共沉淀法制备Li[Li0.2Co0.13Ni0.13Mn0.54]O2中加料方式对产物性能的影响

采用碳酸钠和碳酸氢铵作为沉淀剂和络合剂,在水溶液中共沉淀Mn2+、Ni2+和Co2+以获得混合过渡金属元素的碳酸盐沉淀前驱体Mn0.675Ni0.1625Co0.1625CO3。并进一步合成高容量锂离子电池正极材料Li[Li0.2Co0.13Ni0.13Mn0.54]O2。考察了3种不同加料方式对共沉淀前驱体的结构、形貌和元素比例的影响,以及对最终产物的结构、形貌和电化学性能的影响。     

Synthesis and electrochemical characterization of xLi(Ni0.8Co0.15Mg0.05)O2–(1−x)Li[Li1/3Mn2/3]O2 (0.0 ≤ x ≤ 1.0) cathodes for Li rechargeable batteries

Using solution based processing route, we have successfully synthesized xLi(Ni_0.8Co_0.15Mg_0.05)O₂–(1?x)Li[Li_1/3Mn_2/3]O₂ (0.0 ≤ x ≤ 1.0) cathode materials for lithium rechargeable batteries. The phase formation behavior of these cathode materials is characterized by X-ray diffraction measurements. The Galvanostatic charge–discharge characteristic of these cathodes is reported in various cut-off voltage limits. When these composite cathodes are charged to 4.8 V, electrochemical extraction of lithium takes place from active (Li[Ni_0.8Co_0.15Mg_0.05]O₂) as well as inactive (Li[Li_1/3Mn_2/3]O₂) components. Good cycleability of these cathodes is obtained when cycled in the cut-off voltage limits of 4.6–3.0 V. The cycleability of these cathodes are deteriorated when charged above 4.8 V and deep discharged up to 1.2 V followed by repeated cycling in these voltage limits. Based on the analyses of impedance spectra at various charge and discharge states, the probable reasons for such findings are discussed.     

Synthesis and electrochemical properties of Ca-doped LiNi<Subscript>0.8</Subscript>Co<Subscript>0.2</Subscript>O<Subscript>2</Subscript> cathode material for lithium ion battery

LiNi_0.8Co_0.2O₂ and Ca-doped LiNi_0.8Co_0.2O₂ cathode materials have been synthesized via a rheological phase reaction method. X-ray diffraction studies show that the Ca-doped material, and also the discharged electrode, maintains a hexagonal structure even when cycled in the range of 3.0–4.35 V (vs Li⁺/Li) after 100 cycles. Electrochemical tests show that Ca doping significantly improves the reversible capacity and cyclability. The improvement is attributed to the formation of defects caused by the partial occupancy of Ca²⁺ ions in lithium lattice sites, which reduce the resistance and thus improve the electrochemical properties.     

Effect of the Synthesis Method on the Functional Properties of Lithium-Rich Complex Oxides Li<Subscript>1.2</Subscript>Mn<Subscript>0.54</Subscript>Ni<Subscript>0.13</Subscript>Co<Subscript>0.13</Subscript>O<Subscript>2</Subscript>

Layered Li-rich transition metal oxides are considered among the most promising cathode materials for high energy density lithium-ion batteries. It was studied how the method and conditions of synthesis of Li-rich oxides Li_1.2Mn_0.54Ni_0.13Co_0.13O₂ affect their electrochemical properties. Coprecipitation methods and modified Pechini process were used. It was shown that it is necessary to carefully choose the synthesis conditions when using the modified Pechini method because of their significant effect on the morphology of Li-rich oxides. Samples were obtained with high electrochemical characteristics: capacity discharge of 260–270 mAh/g (16 mA/g) and 60–70 mAh/g (988 mA/g) within the voltage range of 2.5–4.8 V.     

Synthesis of Li3Ni x V2−x (PO4)3/C cathode materials and their electrochemical performance for lithium ion batteries

Li₃Ni _x V_2?x (PO₄)₃/C (x?=?0, 0.02, 0.04 and 0.06) samples have been synthesized via an improved sol–gel method. X-ray diffraction patterns indicate that the structure of the prepared samples retains monoclinic, and the single phase has not been changed with Ni doping. From the analysis of electrochemical performance, the Li₃Ni_0.04?V_1.96(PO₄)₃/C sample exhibits the best electrochemical property. It delivers a discharge capacity of 112.1 mAh?g^?1 with capacity retention of 95.2 % over 300 cycles at 10 C rate in the range of 3.0–4.8 V; cyclic voltammetry and electrochemical impedance spectra testing further prove that the electrochemical reversibility and lithium ion diffusion behavior of Li₃V₂(PO₄)₃ have also been effectively improved through Ni doping.     

Effect of Co substitution for Ni on the microstructure and electrochemical properties of La-R-Mg-Ni-based hydrogen storage alloys

Hydrogen storage alloys La_0.63Gd_0.2?Mg_0.17Ni_3.35?x Co _x Al_0.15 (x?=?0, 0.1, 0.3, 0.5, 1.0, 1.5, 2.0) were prepared by induction melting followed by annealing treatment in argon atmosphere. The electrochemical properties of La_0.63Gd_0.2?Mg_0.17Ni_3.35?x Co _x Al_0.15 (x?=?0, 0.1, 0.3, 0.5, 1.0, 1.5, 2.0) alloy electrodes depended on the alloy structure type. XRD patterns and EPMA showed that the alloys consisted of Ce₂Ni₇-type (Gd₂Co₇-type), CaCu₅-type, Pr₅Co₁₉-type, and PuNi₃-type phase structure. Pr₅Co₁₉-type and Ce₂Ni₇-type phase increased with the increase of Co content x. However, CaCu₅-type phase firstly decreased then increased as Co content increased. Rietveld analysis showed that the c-axis lattice parameters and cell volumes of the component phases increased with increasing Co content. The electrochemical measurements showed that as the Co content increased, the maximum discharge capacity and the cyclic stability of the annealed alloys both first increased and then decreased. The La_0.63Gd_0.2?Mg_0.17Ni_3.05Co_0.3Al_0.15 alloy electrode exhibited the maximum discharge capacity (392.92 mAh/g), and La_0.63Gd_0.2?Mg_0.17Ni_1.85Co_1.5Al_0.15 alloy electrode showed the best cyclic stability (S₁₀₀?=?96.1 %). The electrochemical kinetics studies indicate that La_0.63Gd_0.2?Mg_0.17Ni_1.85Co_1.5Al_0.15 exhibited a higher rate dischargeability (HRD₉₀₀?=?86.3 %). Electrochemical analyses showed that the control process of alloy electrode reaction is charge-transfer rate in surface film of alloy.     

柠檬酸(铵)处理对Li[Li0.2Mn0.54Ni0.13Co0.13]O2电化学性能影响的研究

以共沉淀法制备的[Mn0.54Ni0.13Co0.13]1.25CO3为前驱体,配锂焙烧获得了富锂锰基固溶体Li[Li0.2Mn0.54Ni0.13Co0.13]O2,然后分别用柠檬酸、柠檬酸三铵对该材料进行表面预处理。结果表明经柠檬酸(铵)处理后,Li[Li0.2Mn0.54Ni0.13Co0.13]O2中分别有16.37wt%和13.14wt%的锂被化学脱出。充放电测试结果表明,表面处理后的样品首次效率有了较大的提高(由63.5%分别提高到了80.2%和80.7%),0.2C循环40次容量保持率分别由91.43%提高到97.42%和92.72%,1C容量由处理前的149.5 mAh.g-1提高到179.5mAh.g-1和181.5 mAh.g-1,表明处理后材料的循环性能和倍率性能都得到了改善。这主要是由于柠檬酸(铵)处理,预先脱出了Li2MnO3组分中的部分Li2O,并在材料表面生成了类尖晶石结构的材料。     

Ni0.8Co0.15Al0.05C2O4@Graphene的合成及电化学性能研究

过渡金属氧化物/石墨烯复合材料具有优异的电化学性能被广泛应用在锂离子电池中。本文以硫酸镍、硫酸钴、硫酸铝、草酸为原料按一定的物质的量比配制成溶液,在120°C的条件下水热反应12小时,得到多元过渡金属氧化物前驱体Ni_0.8Co_0.15Al_0.05C₂O₄(NCA-C₂O₄);该前驱体经聚烯丙基胺盐酸盐修饰后,与氧化石墨烯进行复合并还原得到石墨烯包覆的多元过渡金属氧化物/石墨烯负极材料Ni_0.8Co_0.15Al_0.05C₂O₄@Graphene(NCA-C₂O₄@G)。对材料的结构、形貌和电化学性质进行了表征。扫描电镜测试结果显示样品粒度均一,具有两端不规则长方体形貌。电化学性能测试结果表明：石墨烯包覆后的NCA-C₂O₄@G充放电容量高于前驱体NCA-C₂O₄,NCA-C₂O₄@G复合材料在0.1C电流密度 (1C=1000 mAh/g)下首次放电比容量为1956 mA h/g;经过0.1C、0.2C、0.5C、1C、2C高倍率循环后,当测试电流密度恢复至100 mA/g时,复合材料比容量可迅速回升至720 mA h/g,并在随后50次循环中比容量保持稳定,显示出良好的循环稳定性和倍率性能。