Eliminating H_(2)O/HF and regulating interphase with bifunctional tolylene-2,4-diisocyanate(TDI)additive for long life Li-ion battery

Lithium-ion batteries(LIBs)featuring a Ni-rich cathode exhibit increased specific capacity,but the establishment of a stable interphase through the implementation of a functional electrolyte strategy remains challenging.Especially when the battery is operated under high temperature,the trace water present in the electrolyte will accelerate the hydrolysis of the electrolyte and the resulting HF will further erode the interphase.In order to enhance the long-term cycling performance of graphite/LiNi_(0.8)Co_(0.1)Mn_(0.1)O_(2)(NCM811)LIBs,herein,Tolylene-2,4-diisocyanate(TDI)additive containing lone-pair electrons is employed to formulate a novel bifunctional electrolyte aimed at eliminating H_(2)O/HF generated at elevated temperature.After 1000 cycles at 25℃,the battery incorporating the TDI-containing electrolyte exhibits an impressive capacity retention of 94%at 1 C.In contrast,the battery utilizing the blank electrolyte has a lower capacity retention of only 78%.Furthermore,after undergoing 550 cycles at 1 C under45℃,the inclusion of TDI results in a notable enhancement of capacity,increasing it from 68%to 80%.This indicates TDI has a favorable influence on the cycling performance of LIBs,especially at elevated temperatures.The analysis of the film formation mechanism suggests that the lone pair of electrons of the isocyanate group in TDI play a crucial role in inhibiting the generation of H_(2)O and HF,which leads to the formation of a thin and dense interphase.The existence of this interphase is thought to substantially enhance the cycling performance of the LIBs.This work not only improves the performance of graphite/NCM811 batteries at room temperature and high temperature by eliminating H_(2)O/HF but also presents a novel strategy for advancing functional electrolyte development.

Supercritical-hydrothermal accelerated solid state reaction route for synthesis of LiMn_2O_4 cathode material for high-power Li-ion batteries

Synthesis of the spinel structure lithium manganese oxide （LiMn2O4） by supercritical hydrothermal （SH） accelerated solid state reaction （SSR） route was studied. The impacts of the reaction pressure, reaction temperature and reaction time of SH route, and the calcination temperature of SSR route on the purity, particle morphology and electrochemical properties of the prepared LiMn2O4 materials were studied. The experimental results show that after 15 min reaction in SH route at 400 ℃ and 30 MPa, the reaction time of SSR could be significantly decreased, e.g. down to 3 h with the formation temperature of 800 ℃, compared with the conventional solid state reaction method. The prepared LiMn2O4 material exhibits good crystallinity, uniform size distribution and good electrochemical performance, and has an initial specific capacity of 120 mA.h/g at a rate of 0.1C （1C=148 mA/g） and a good rate capability at high rates, even up to 50C.

Synthesis and characterization of phosphate-modified LiMn_2O_4 cathode materials for Li-ion battery

LiMn2O4 spinel cathode materials were modified with 2 wt.%Li-M-PO4（M=Co,Ni,Mn） by polyol synthesis method.The phosphate surface-modified LiMn2O4 cathode materials were physically characterized by X-ray diffraction（XRD）,scanning electron microscopy（SEM） and energy dispersive X-ray spectroscopy（EDS）.The charge-discharge test showed that the cycling and rate capacities of LiMn2O4 cathode materials were significantly enhanced by stabilizing the electrode surface with phosphate.

Electrochemical performance of SrF_2-coated LiMn_2O_4 cathode material for Li-ion batteries

SrF2-coated LiMn2O4 powders with excellent electrochemical performance were synthesized. The electrochemical performance of SrF2-coated LiMn2O4 electrodes was studied as function of the level of SrF2 coating. With increasing the amount of the coated-SrF2 to 2.0% (molar fraction), the discharge capacity of LiMn2O4 decreases slightly, but the cycleability of LiMn2O4 at elevated temperature is improved obviously. In view of discharge capacity and cycleability, the 2.0% (molar fraction) coated sample shows optimum cathodic behaviors. When being cycled at 55 ℃, as-prepared LiMn2O4 remains only 79% of its initial capacity after 20 cycles, whereas the 2.0% (molar fraction) coated sample shows initial discharge capacity of 108 mA·h/g, and 97% initial capacity retention.

Electrochemical Characterization of Surface-modified LiMn_2O_4 Cathode Materials for Li-ion Batteries

To improve the performance, the surface of 12Mn2O4 was coated with very fine MgO , Al2O3 and ZnO by solgel method, respectively. The structure and morphology of the coated materials were investigated by X-ray diffraction （ XRD ）, X-ray photoelectron spectroscopy （ XPS ） and scanning electron microscopy （SEM）. The charge and discharge performance of uncoated and surfnce modified 12Mn2O4 spinel at 25℃ and 55 ℃ were tested, using a voltage window of 3.0-4.35 V and a current deasity of 0. 1 C rate. There is a slight decrease in the initial discharge capacity relative to that of uncoated UMn2 O4, bat the cycle ability of 12 12Mn2O4 coated by metal-oxide has remarkably been improved. The EIS measuremeuts of uncoated and Al2O3 -coated 12Mn2O4 were carried out by a model 273 A potentiostatl galvanistat controUed by a computer using M270 software, and using a freqnency response analyzer （ Zsimpwin ） combined with a potentiostate （ PAR 273）. Coaseqnently, the reason for the improved cycle properties is that the surface modification reduces the dissolution of Mn , which results from the suppression of the electrolyte decomposition, and suppresses the formation of passivation film that acts as an electronic insulating layer. In conclusion, the use of surface modification is an effective way to improve the electrochemical performance of 12Mn2O4 cathode material for lithium batteries.

Performance and capacity fading reason of LiMn_2O_4/graphite batteries after storing at high temperature

Spinel LiMn204 was synthesized by a solid-state method. A 204468-size battery was fabricated and stored at 55℃. The structure and morphology of the LiMn204 cathode were analyzed by X-ray diffraction （XRD） and scanning electron microscopy （SEM） technique. Energy dispersive spectroscopy （EDS） was used to analyze the surface component of the carbon anode. The discharge capacities of LiMn204 stored for 0, 24, 48, and 96 h are 106, 98, 96, and 92 mAh·g^-1, respectively. The cyclic performance is improved after storage. The capacity retentions of LiMn204 stored for 0, 24, 48, and 96 h are 83.8%, 85.8%, 86.9%, and 88.6% after 180 cycles. The intensity of all the LiMn204 diffraction peaks is weakened. Mn is detected from the carbon electrode when the battery is stored for 96 h. Cyclic voltammograms and electrochemical impedance spectroscopy （EIS） were used to examine the surface state of the electrode after storage. The results show that the resistance and polarization of LiMn2O4/electrolyte is increased after storage, which is responsible for the fading of capacity.

Effects of sodium substitution on properties of LiMn_2O_4 cathode for lithium ion batteries

Na-doped Li1.05Mn2O4 cathodes were synthesized using a sol-gel process.The samples were characterized by X-ray diffractometry(XRD),cyclic voltammetry(CV),electrochemical impedance spectroscopy(EIS)and charge-discharge measurements. The results show that all the samples exhibit the same cubic spinel phase structure without impurity.The lattice constant and unit cell volume decrease with increasing the sodium dopant amount.As the molar ratio of sodium to manganese(x=n(Na)/n(Mn))increases from 0 to 0.03,the initial discharge capacity of the Li1.05Mn2O4 cathodes decreases from 119.2 to 107.9 mA·h/g,and the discharge capability at large current rate and the storage performance decline dramatically,while cycling performance at room temperature and 55℃are improved.The CV and EIS studies indicate that reversibility of Li1.05Mn2O4 cathodes decreases and the electrochemical impedance increases with increasing the sodium dopant amount.

Overcharge performance of LiMn_2O_4/graphite battery with large capacity

The LiMn2O4/grapbite battery was fabricated and its 3 C/10 V overcharge performance was studied. Spinel LiMn2O4 was synthesized by solid-state method and 325680-type size full battery was fabricated. The structure and morphology of the powders were characterized by XRD and SEM technique, respectively. The battery explodes after 3 C/10 V overcharged test, and surface temperature of the battery case arrives at 290 ℃ in 12 s after exploding. Black air is given out with blast. Carbon, MnO, and Li2CO3 are observed in the exploded powders. The cathode electrode remains spinel structure with 5.0 V charged. Cracks in the cathode electrode particles are detected with the increase of voltage by SEM technique. The 5.0 V charged electrode can decompose into Mn3O4 at 400 ℃. It is demonstrated that the decomposition of 5.0 V charged electrode can be promoted and Mn^4＋ can be deoxidized to Mn^2＋ by carbon and electrolyte through the simulation of blast process.

Preparation and characterization of spinel LiMn_2O_4 nanorods as lithium-ion battery cathodes

The hydrothermal synthesis of single-crystallineβ-MnO2 nanorods and their chemical conversion into single-crystalline LiMn2O4 nanorods by a simple solid-state reaction were reported.This method has the advantages of producing pure,single-phase and crystalline nanorods.The LiMn2O4 nanorods have an diameter of about 300 nm.The discharge capacity and cyclic performance of the batteries were investigated.The LiMn2O4 nanorods show better cyclic performance with a capacity retention ratio of 86.2% after 100 cycles.Battery cyclic studies reveal that the prepared LiMn2O4 nanorods have high capacity with a first discharge capacity of 128.7 mA·h/g.

Characteristics of LiCoO2, LiMn2O4 and LiNi0.45Co0.1Mn0.45O2 as cathodes of lithium ion batteries

LiNi0. 45 Co0. 10 Mn0. 4sO2 was synthesized from Li2CO3 and a triple oxide of nickel, cobalt and manganese at 950 ℃ in air. The structures and characteristics of LiNi0. 45 Co0.10 Mn0. 45 O2, LiCoO2 and LiMn2 O4 were investigated by XRD, SEM and electrochemical measurements. The results show that LiNi0.4s Co0.10 Mn0. 45 O2 has a layered structure with hexagonal lattice. The commercial LicoO2 has sphere-like appearance and smooth surfaces, while the LiMn2 O4 and LiNi0.45 Co0. 10 Mn0. 45 O2 consist of cornered and uneven particles. LiNi0. 45 Co0.10 Mn0. 45 O2 has a large disLiMn2 O4 and LiCoO2, respectively. LiCoO2 and LiMn2 O4 have higher discharge voltage and better rate-capability than LiNi0. 45Co0.10 Mn0. 45 O2. All the three cathodes have excellent cycling performance with capacity retention of above 89.3 % at the 250th cycle. Batteries with LiMn2 O4 or LiNi0.45 Co0.10 Mn0. 45 O2 cathodes show better safety performance under abusive conditions than those with LiCoO2 cathodes.

Influence on performance and structure of spinel LiMn2O4 for lithium-ion batteries by doping rare-earth Sm

The spinel LiMn2O4 used as cathode materials for lithium-ion batteries was synthesized by mechanochemistry fluid activation process, and modified by doping rare-earth Sm. Testing of X-ray diffraction, cyclic voltammograms, charge-discharge and SEM was carried out for LiMn2O4 cathode materials and the modified materials.The results show that the cathode materials doped rare earth LixMn2-ySmxO4 (0.95≤x≤1.2, 0≤y≤0.3, 0≤z≤0.2) exhibit standard spinel structure, high reversibility of electrochemistry and excellent properties of charge-discapacity is deteriorated less than 15% after 300 cycles at room temperature and less than 20% after 200 cycles at 55 C.At the same time, Crystal Field Theory was applied to explain the function and mechanism of doped rare earth element.

LiMn_2O_4 thin films derived by rapid thermal annealing and their performance as cathode materials for Li ion battery

The LiMn2O4 thin film as a cathode material was prepared through solution deposition followed by rapid thermal annealing （RTA）. The phase identification and the study of surface morphology were carried out by X-my diffraction and scanning electron microscopy. Electrochemical properties were examined by cyclic voltammetry, galvanostatic charge-discharge experiments, and electrochemical impedance spectroscopy. The results show that the film prepared by this method is homogeneous, dense, and crack-free. The thin film has a capacity of 38 μtAh/（cm^2·μm） with the capacity loss of 0.037% per cycle after being cycled for 100 times. The average diffusion coefficient for lithium ions in the RTA-derived LiMn2O4 thin film is 1×10 ^-10 cm^2·s^-1.

The design and fabrication of Co3O4/Co3V2O8/Ni nanocomposites as high-performance anodes for Li-ion batteries

The CoO/CoVO/Ni nanocomposites were rationally designed and prepared by a two-step hydrothermal synthesis and subsequent annealing treatment. The one-dimensional（1D） CoOnanowire arrays directly grew on Ni foam, whereas the 1D CoVOnanowires adhered to parts of CoOnanowires.Most of the hybrid nanowires were inlayed with each other, forming a 3D hybrid nanowires network.As a result, the discharge capacity of CoO/CoVO/Ni nanocomposites could reach 1201.8 mAh/g after100 cycles at 100 mA/g. After 600 cycles at 1 A/g, the discharge capacity was maintained at 828.1 mAh/g.Moreover, even though the charge/discharge rates were increased to 10 A/g, it rendered reversible capacity of 491.2 mAh/g. The superior electrochemical properties of nanocomposites were probably ascribed to their unique 3D architecture and the synergistic effects of two active materials. Therefore, such CoO/CoVO/Ni nanocomposites could potentially be used as anode materials for high-performance Li-ion batteries.

Electrochemical properties of high-power lithium ion batteries made from modified spinel LiMn_2O_4

A prismatic 204056-type high power lithium-ion battery was developed.Modified LiMn2O4 and carbonaceous mesophase sphere(CMS)were adopted as the cathode and anode,respectively.The effects of proportion of conductive carbon black in cathode and the rest time after discharge on the electrochemical properties of batteries were investigated.The electrochemical tests show that the proportion of conductive carbon black in cathodes affects the high rate capability and discharge voltage plateau distinctly.The battery with 3.0%of conductive carbon black in cathode shows excellent electrochemical performances when being charged/discharged within 2.5-4.2 V at room temperature.The discharge capacity at 20C rate is 94.4%of that at 1C rate,and the capacity retention ratio charged at 1C and discharged at 5C is 86.6%after 390 cycles at room temperature.The test result of impulse discharge at 50C for 5 s shows that the battery has outstanding high rate discharge performance when the battery is in the depth of charge of 90%,75%,60%,45%,30%and 15%.The battery also shows good charge performance.When the battery is charged at 0.5C,1C,2C and 4C,the ratios of capacity for constant current charge are 98.4%,96.4%,91.0%and 72.9%of the whole charge capacity,respectively.In addition,the rest time after discharge affects the cycle performance distinctly when the battery is discharged at high rate.

Controllable Preparation and Superior Rate Performance of Spinel LiMn2O4 Hollow Microspheresas Cathode Material for Lithium-ion Batteries

Spinel LiMn2O4 microspheres and hollow microspheres with adjustable wall thickness have been prepared using controllable oxidation of MnCO3 microspheres precursors and following solid reactions with lithium salts. Scanning electron microscopy （SEM） investigations demonstrate that the microsphere morphology and hollow structure of precursors are inherited. The effect of hollow structure properties of as-prepared LiMn2O4 on their performance as cathode materials for lithium-ion batteries has been studied. Electrochemical performance tests show that LiMn2O4 hollow microspheres with small wall thickness exhibit both superior rate capability and better cycle performance than LiMn2O4 solid microspheres and LiMn2O4 hollow microspheres with thick wall. The LiMn2O4 hollow microspheres with thin wall have discharge capacity of 132.7 mA.h-g^-1 at C/10 （14.8 mA.g^-1） in the first cycle, 94.1% capacity retention at C/10 after 40 cycles and discharge capacity of 116.5 mAh-gq at a high rate of 5C. The apparent lithium-ion diffusion coefficient （Dapp） of as-prepared LiMn2O4 determined by capacity intermittent titration technique （CITT） varies from 10-11 to 10-8.5 cm2.s^-1 showing a regular ＂W＂ shape curve plotted with test voltages. The D app of LiMn2O4 hollow microspheres with thin wall has the largest value among all the prepared samples. Both the superior rate capability and cycle stability of LiMn2O4 hollow microspheres with thin wall can be ascribed to the facile ion diffusion in the hollow structures and the robust of hollow structures during repeated cycling.

Synthesis and Properties of Li_2MnSiO_4/C Cathode Materials for Li-ion Batteries

Carbon was coated on the surface of LiMnSiOto improve the electrochemical performance as cathode materials, which were synthesized by the solution method followed by heat treatment at 700 ℃ and the solid-state method followed by heat treatment at 950 ℃. It is shown that the cycling performance is greatly enhanced by carbon coating, compared with the pristine LiMnSiOcathode obtained by the solution method. The initial discharge capacity of LiMnSiO/C nanocomposite is 280.9 m Ah/g at 0.05 C with the carbon content of 33.3 wt%. The reasons for the improved electrochemical performance are smaller grain size and higher electronic conductivity due to the carbon coating. The LiMnSiO/C cathode material obtained by the solid-state method exhibits poor cycling performance, the initial discharge capacity is less than 25 m Ah/g.

Enhanced High-Temperature Cycling Stability of LiMn<SUB>2</SUB>O<SUB>4</SUB>by LiCoO<SUB>2</SUB>Coating as Cathode Material for Lithium Ion Batteries

LiCoO2 surface layer is proposed and prepared through sol-gel method. The physical and electrochemical performances of pristine LiMn2O4 and LiCoO2-coated LiMn2O4 cathode materials were investigated by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, electrochemical measurements respectively. Comparing with the pristine LiMn2O4, the LiCoO2- coated LiMn2O4 phase significantly improved cycling stability, especially at 55°C. Additionally, the thermal safety of LiMn2O4 is greatly enhanced after being coated by LiCoO2. ICP-AES measurement, structural analysis, and impedance experiments indicate that the improved electrochemical property of LiCoO2-coated LiMn2O4 should be attributed to the alleviated dissolution loss of manganese, strengthened structural stability.

纳米级LiMn_2O_4尖晶石合成及电化学性能研究

以Ｌｉ２ＣＯ３和Ｍｎ（ＮＯ３）２为原料，以聚丙烯酰胺为高分子网络剂制得前驱体后，用微波加热技术合成了纳米晶尖晶石ＬｉＭｎ２Ｏ４粉体，通过循环伏安及充放电技术对其进行电化学性能测试表明，该材料的电化学比容量为 １２０ｍＡｈ／ｇ；循环 ５０次后衰减率为 ４．７％；通过 ＳＥＭ及ＸＲＤ分析其微观形貌表明，该材料不仅相纯度高，而且颗粒粒度近于纳米级，有利于Ｌｉ＋的嵌入／脱嵌．本文所提供的微波一高分子网络技术不仅为合成具有优良性能的锂锰尖晶石氧化物材料提供了一个新方法，而且为合成其他类型高性能氧化物陶瓷材料提供了一条新思路．

锂离子电池正极材料LiMn_2O_4的研究进展

具有尖晶石相的LiMn2O4因价格低、无毒、无环境污染、制备简单、研究较成熟,因此有着很好的应用前景,被看作最有可能成为新一代商用锂离子二次电池正极材料.由于LiMn2O4电化学循环稳定性能不好,表现在可逆容量衰减较大,尤其在高温下(>55℃)使用衰减更严重,从而限制了它的商业化应用.经过近十几年的研究,人们对其衰减机理有了比较清晰的了解,提出了造成容量衰减的几种可能原因如Jahn-Teller畸变效应、Mn2+在电解质中的溶解、出现稳定性较差的四方相以及电解质的分解等.通过掺杂、表面包覆、制备工艺的改进,人们已能制得循环稳定性能较好的尖晶相材料.本文结合我们研究小组的最新研究成果对锂离子二次电池正极材料LiMn2O4的最新研究进展进行综述和评论.

LiMn_2O_4正极在高温下性能衰退现象的研究

采用恒流充放电方法测量了温度升高导致ＬｉＭｎ２Ｏ４正极容量衰减的情况．发现当环境温度上升到５０℃时，ＬｉＭｎ２Ｏ４电极出现严重的容量损失和性能衰退，充电态的电极受影响的程度最为严重．对电解液的原子发射和红外光谱分析，电极晶相结构Ｘ＿射线衍射及循环伏安实验研究表明：随着温度升高，ＬｉＭｎ２Ｏ４中阳离子混乱度增大形成无序尖晶石结构，锰离子的溶解度迅速增加，电解液出现催化氧化是导致容量不可逆衰减的原因．