Effects of different precipitants on LiNi<Subscript>0.5</Subscript>Mn<Subscript>1.5</Subscript>O<Subscript>4</Subscript> for lithium ion batteries prepared by modified co-precipitation method

Effects of two different precipitants of Na₂CO₃ and Na₂C₂O₄ on LiNi_0.5Mn_1.5O₄ (LNMO) cathode materials, which are prepared by a modified co-precipitation method, have been investigated. Various measurements have been applied to characterize the physical and electrochemical performances of LNMO. Compared with the LNMO prepared by the oxalate co-precipitation (LNMO2), the material synthesized by the carbonate co-precipitation (LNMO1) not only shows more uniform porosity and smaller particles but also has a better rate capability and cycling performance. In addition, the sample prepared by carbonate has a stable spherical structure, due to the fact that carbonate co-precipitation with less gas release during calcination can prevent the destruction of the as-prepared LNMO material structure and promote the formation of regular particle and aperture. Based on the electrochemical test results, LNMO1 shows greatly enhanced electrochemical performance of a high initial discharge capacity of 125.6 mAh g^?1 at 0.25 °C, as well as a preferably capacity retention of 96.5% after 100 cycles at 0.5 °C. And even at a high rate of 10 °C, the discharge capacity of LNMO1-based cell still approaches 83.1 mAh g^?1.     

Effect of heptamethyldisilazane on the electrochemical performance of LiMn2O4/Li

The effect of heptamethyldisilazane as an electrolyte stabilizer on the cycling performance of a LiMn₂O₄/Li cell at different rates at 30 °C and the storage performance at 60 °C is investigated systematically based on conductivity test, linear sweep voltage, electrochemical impedance spectroscopy, scanning electron microscopy, X-ray diffraction, and charge–discharge measurements. The results show that heptamethyldisilazane added into the LiPF₆-based electrolyte can increase the stability of the original electrolyte; coulomb efficiency, the initial discharge capacity, and cycling performance at different rates in a sense, meanwhile, improve the storage performance at elevated temperature, although the C-rate performance of the cell is a little worse than that without heptamethyldisilazane in the electrolyte. When the LiMn₂O₄/Li cell with heptamethyldisilazane in the LiPF₆-based electrolyte stored at 60 °C for a week cycles 300 times, the capacity retention is up to 91.18 %, which is much higher than that (87.18 %) without the additive in the electrolyte. This is mainly due to the lower solid electrolyte interface resistance (R _f) in the cell, followed by the better morphology and structure of the cathode after storage at 60 °C for a week compared with the LiMn₂O₄/Li cell without heptamethyldisilazane.     

A lithium salt additive Li<Subscript>2</Subscript>ZrF<Subscript>6</Subscript> for enhancing the electrochemical performance of high-voltage LiNi<Subscript>0.5</Subscript>Mn<Subscript>1.5</Subscript>O<Subscript>4</Subscript> cathode

In this work, Li₂ZrF₆, a lithium salt additive, is reported to improve the interface stability of LiNi_0.5Mn_1.5O₄ (LNMO)/electrolyte interface under high voltage (4.9 V vs Li/Li⁺). Li₂ZrF₆ is an effective additive to serve as an in situ surface coating material for high-voltage LNMO half cells. A protective SEI layer is formed on the electrode surface due to the involvement of Li₂ZrF₆ during the formation of SEI layer. Charge/discharge tests show that 0.15 mol L^?1 Li₂ZrF₆ is the optimal concentration for the LiNi_0.5Mn_1.5O₄ electrode and it can improve the cycling performance and rate property of LNMO/Li half cells. The results obtained by electrochemical impedance spectroscopy (EIS), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS) demonstrate that Li₂ZrF₆ can facilitate the formation of a thin, uniform, and stable solid electrolyte interface (SEI) layer. This layer inhibits the oxidation decomposition of the electrolyte and suppresses the dissolution of the cathode materials, resulting in improved electrochemical performances.     

Enhanced electrochemical performance of lithium vanadium phosphate as cathode by LiBOB/LiTFSI with additive in EC/EMC

A series of Li₃V₂(PO₄)₃/C (LVP/C) samples with monoclinic structure indexed to P2₁/n space group were synthesized using V₂O₃ as vanadium source by solid state reaction method by different sintering temperatures. It was found that the LVP/C sintered at 750 °C with a carbon content 3 wt.% was the optimum condition for this synthesis. The structural, morphological, superficial, and textural properties of LVP/C were characterized by XRD, SEM, TEM, and XPS. The electrochemical performance was evaluated by galvanostatic charge–discharge cycling using new high voltage electrolyte. The optimized cell delivered an initial discharge capacity of 187 mAh g^?1 in the higher cut-off voltage of 3.0–4.8 V vs. Li⁺/Li⁰ at 0.2 C rate, with a capacity retention of 88 %, 89 %, and 61 % after 50 cycles discharging at 1 C, 2 C, and 4 C, respectively. The capacity can be almost recovered at 0.5 C after long cycles. The excellent stability is contributed to the new high-voltage electrolyte.     

Influence of charge rate on the cycling degradation of LiFePO<Subscript>4</Subscript>/mesocarbon microbead batteries under low temperature

The lithium-ion batteries show extremely poor cycling performance at low temperature. The main degradation mechanism is not clear. To address the fading mechanism, the cycling degradation of commercial LiFePO₄/mesocarbon microbead (MCMB) batteries under various charge rate (1/10C, 1/3C, 1/2C, and 1C) at ?10 °C is systematically investigated using nondestructive tests combining with post-mortem analysis. The low-temperature charging under high charge rates of 1/3C, 1/2C, and 1C results in severe lithium plating, which leads to extremely serious capacity loss. In contrast, no lithium plating occurred under low charge rate of 1/10C. The lithium plating on the anode surface leads to consumption of active lithium ions and electrolyte, which causes the capacity decay and increases ohmic resistance (R _b) with cycling number under high charge rates. The lithium plating on the anode surface is partially reversible, which brings about the capacity recovery of batteries after 80 cycles at 25 °C. The above results are proved by the followed post-mortem measurements. The evolution of the surface morphologies of MCMB electrodes upon cycling shows that a layer composed of rod-like lithium is formed on the anode surface.     

Enhanced electrochemical performance of LiFePO4/C prepared by sol–gel synthesis with dry ball-milling

LiFePO₄/C was prepared by a modified aqueous sol–gel route developed by incorporating an additional ball-milling step where the dry gel was milled with the additives of synthetic graphite and carbon black. The materials were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), Brunauer–Emmett–Teller (BET), transmission electron microscopy (TEM), high resolution TEM (HRTEM) and elemental analysis. Results showed that the LiFePO₄/C synthesized by suitable ball-milling process had pure, fine and homogenous LiFePO₄ particles. Results of cyclic voltammetry and charge/discharge plateaus demonstrated that the LiFePO₄/C composite synthesized by milling for 2 h had much better electrochemical kinetics. High performances were achieved with its discharge capacities of 157 mA h g^?1 at 0.1?C and 133 mA h g^?1 at 1?C between 2.5 and 4.2 V (1?C?=?170 mA g^?1). And no obvious capacity fading was observed upon cycling. The simple and convenient synthesis route is promising for large-scale production of LiFePO₄/C.     

LiNi<Subscript>0.5</Subscript>Mn<Subscript>1.5</Subscript>O<Subscript>4</Subscript> hollow nano-micro hierarchical microspheres as advanced cathode for lithium ion batteries

The high-voltage spinel-type LiNi_0.5Mn_1.5O₄ (LNMO) is a promising cathode material for next-generation lithium ion batteries. In this study, hollow LNMO microspheres have been synthesized via co-precipitation method accompanied with high-temperature calcinations. The physical and electrochemical properties of the materials are characterized by x-ray diffraction (XRD), TGA, RAMAN, CV, scanning electron microscope (SEM), transmission electon microscopy (TEM), electrochemical impendence spectroscopy (EIS), and charge-discharge tests. The results prove that the microspheres combine hollow structures inward and own a cubic spinel structure with space group of Fd-3m, high crystallinity, and excellent electrochemical performances. With the short Li⁺ diffusion length and hollow structure, the hierarchical LNMO microspheres exhibit 138.2 and 108.5 mAh g^?1 at 0.5 and 10 C, respectively. Excellent cycle stability is also demonstrated with more than 98.8 and 88.2 % capacity retention after 100 cycles at 1 and 10 C, respectively.     

Investigation on LiNi<Subscript>0.5</Subscript>Mn<Subscript>1.5</Subscript>O<Subscript>4</Subscript> cathode material based on the precursor of nickel-manganese compound for lithium-ion battery

The high-voltage spinel LiNi_0.5Mn_1.5O₄ (LNMO) with submicron particle size (LNMO-850₅P700₁₀) has been synthesized based on nickel-manganese compound, which is obtained from pre-sintering the nickel-manganese hydroxide precipitation at 850 °C. The LNMO materials based on nickel-manganese hydroxide (LNMO-700₁₀, LNMO-850₅700₁₀, and LNMO-850₁₀700₁₀) have also been synthesized for comparison to study the pre-sintering impact on the properties of LiNi_0.5Mn_1.5O₄ material. The morphologies and structures of the obtained samples have been analyzed by X-ray powder diffraction and scanning electron microscopy. The nickel-manganese compound has a spinel structure with high crystallinity, making it a good precursor to form high-performance LNMO with lower content of Mn³⁺ and impurity. The obtained LNMO-850₅P700₁₀ delivers discharge capacities of 125.4 mA h g^?1 at 0.2 C, and the capacity retention of 15 C reaches 73.8 % of the capacity retention of 0.2? C. Furthermore, it shows a superior cyclability with the capacity retention of 96.4 % after 150 cycles at 5 ?C. Compared with the synthesis method without pre-sintering, the synthesis method with pre-sintering can save energy while reaching the same discharge specific capacity.     

Preparation and characterization of LiTi<Subscript>2</Subscript>O<Subscript>4</Subscript> anode material synthesized by one-step solid-state reaction

LiTi₂O₄ anode material for lithium-ion battery has been prepared by a novel one-step solid-state reaction method using Li₂CO₃, TiO₂, and carbon black as raw materials. X-ray diffraction, scanning electron microscopy, energy-dispersive spectrometry, and the determination of electrochemical properties show that the single phase of LiTi₂O₄ with spinel crystal structure is formed at 850?°C by this new method, and the lattice parameter is about 8.392?Å. The primary particle size of the LiTi₂O₄ powder is about 0.5–1.0 μm and its morphology is similar to a sphere. The lithium ion insertion voltage of LiTi₂O₄ anode material is about 1.50 V versus lithium metal, the initial discharge capacity is about 133.6 mAh g^-1, the charge–discharge voltage plateau is very flat, and no solid electrolyte interface film is formed when working potential is more than 1.0 V. The reaction reversibility and the cycling stability are excellent, and the high rate performance is good.     

An approach to improve the electrochemical performance of LiMn<Subscript>2</Subscript>O<Subscript>4</Subscript> at high temperature

In order to overcome the severe capacity decay of LiMn₂O₄ at high temperature, TiN is used as an active materials additive in this paper. The XRD and XPS test results indicate that the TiN can effectively prevent Mn from dissolving in electrolyte; galvanostatic charge-discharge test shows that LiMn₂O₄ electrode with TiN exhibits remarkably improved capacity retention at high temperature with capacity of 105.1 mAh g^?1 at 1 C in the first cycle at 55 °C and the capacity maintains 88.9% retention after 150 cycles. And the electrochemical impedance spectroscopy result demonstrates TiN’s effectiveness in easing the increase of charge-transfer resistance during cycling. Therefore, we can conclude that TiN, as an addictive, made obvious contribution to the greatly improved electrochemical cycling performance of LiMn₂O₄.     

CeO<Subscript>2</Subscript> coating to improve the performance of Li[Li<Subscript>0.2</Subscript>Mn<Subscript>0.54</Subscript>Ni<Subscript>0.13</Subscript>Co<Subscript>0.13</Subscript>]O<Subscript>2</Subscript>

The Li[Li_0.2Mn_0.54Ni_0.13Co_0.13]O₂ coated with CeO₂ has been fabricated by an ionic interfusion method. Both the bare and the CeO₂-coated samples have a typical layered structure with R-3m and C2/m space group. The results of XRD and TEM images display that the CeO₂ coating layer on the precursor could enhance the growth of electrochemically active surface planes ((010), (110), and (100) planes) in the following ionic interfusion process. The results of galvanostatic cycling tests demonstrate that the CeO₂-coated sample has a discharge capacity of 261.81 mAh g^?1 with an increased initial Coulombic efficiency from 62.4 to 69.1% at 0.05 °C compared with that of bare sample and delivers an improved capacity retention from 71.7 to 83.4% after 100 cycles at 1 °C (1 °C?=?250 mA g^?1). The results of electrochemical performances confirm that the surface modification sample exhibits less capacity fading, lower voltage decay, and less polarization.     

Preparation,properties, and Li-ion battery application of EC + PC-modified PVdF-HFP gel polymer electrolyte films

Based on poly(vinylidene fluoride-co-hexafluoropropylene) (PVdF-HFP) and lithium tetrafluoroborate (LiBF₄) salt along with blending plasticizers, ethylene carbonate (EC) and propylene carbonate (PC), high Li-ion-conducting gel polymer electrolyte films are developed. Their properties are characterized by various techniques. The ambient temperature ionic conductivity of the 85PVdF-HFP:15LiBF₄ + 150(EC + PC) electrolyte film has a high value of 8.1 × 10^?4 S cm^?1. Its crystallinity, melting point, and electrochemical stability window are 9.5%, 115 °C, and 4.6 V, respectively. The mechanical testing shows that the Young’s modulus, yield strength, and breaking strain of this electrolyte film are 36.8 MPa, 3.4 MPa, and 320%, respectively. Lithium-ion batteries based on the gel polymer electrolyte film exhibit remarkable charge–discharge and cycling performances. The initial discharge capacity of this battery is as high as 165.1 mAh g^?1 at 0.1 C and just shows a small capacity fading of 4.8% after 120 cycles, indicating that the 85PVdF-HFP:15LiBF₄ + 150(EC + PC) system is an excellent electrolyte candidate for lithium-ion battery applications. The charge–discharge performance of the Li-ion cell fabricated with this gel polymer electrolyte film is apparently better than that of the previously reported Li-ion cells fabricated with other PVdF-HFP-based gel polymer electrolyte films.     

Electrochemical properties of intermediate-temperature SOFCs based on proton conducting Sm-doped BaCeO3 electrolyte thin film

Dense BaCe_0.8Sm_0.2O_2.90 (BCSO) thin films were successfully fabricated on porous NiO–BCSO substrates by dry pressing process. As characterized by scanning electron microscope, the BCSO films were about 50 μm. With Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3−δ (BSCF) as cathodes, single cells were tested at 600 and 700 °C with humidified (3% HB₂O) hydrogen as fuel and oxygen as oxidant. The open circuit voltage of 1.049 V at 600 °C and 1.032 V at 700 °C were achieved, indicating negligible gas permeation through the BCSO thin films. Maximum power densities of 132 and 340 mW/cm² were obtained at 600 and 700 °C, respectively. The impedance measurements at open circuit conditions showed that there were two rate-limiting processes for the electrode reactions and that the cell performances were essentially determined by the electrode polarization resistances at temperature below 650 °C, which implied that it was essential to reduce the electrode polarization by developing novel electrode materials to improve the performance of ITSOFC based on BCSO electrolyte. Conductivities of BCSO under the cell operating circumstances were obtained as 0.00416, 0.00662 and 0.00938 Scm^− 1 at 500, 600 and 700 °C, respectively. The activation energy of BCSO conductivity was calculated as 29.5 and 43.8 kJ/mol for the temperature range of 550–700 °C and of 400–550 °C, respectively. Endurance test was firstly carried out with 75 μm BCSO electrolyte at 650 °C at the operating voltage of 0.7 V and current density about 0.12 A/cm². Both voltage and current density remained stable for 1000 min.     

Effect of annealing time on properties of spinel LiNi<Subscript>0.5</Subscript>Mn<Subscript>1.5</Subscript>O<Subscript>4</Subscript> high-voltage lithium-ion battery electrode materials prepared by co-precipitation method

In this wok, a series of LiNi_0.5Mn_1.5O₄ (LNMO) samples with an octahedral shape entirely composed of (111) crystal planes were prepared by calcining the mixture of the precursor Ni_0.25Mn_0.75(OH)₂ and LiOH·H₂O at 800 °C for 15 h in air, followed by annealing them at 600 °C for different dwelling times. Powder X-ray diffraction (XRD), scanning electron microscopy (SEM), and several electrochemical technologies were used to investigate the effect of annealing time on properties of the LNMO samples. XRD analysis indicates that the lattice parameters of the LNMO samples show a decreasing trend with increasing of annealing time, and the impurity peaks become less apparent for the sample annealed for 6 h and almost disappear for the samples annealed for 9 and 24 h. SEM results show that the annealing time has no obvious influence on the morphologies of the LNMO samples. Electrochemical measurements show that the electrochemical performances (capacity, cycle life, and rate capability) of the samples annealed for 6, 9, and 24 h are better than those of the unannealed sample, and the sample annealed for 9 h shows the best electrochemical properties among them due to its superior electrochemical kinetics of Li⁺ insertion/desertion.     

Structure and electrochemical performance of LiCoO2 cathode material in different voltage ranges

LiCoO₂ sample prepared by high-temperature solid state calcination shows a typical hexagonal structure with a single phase and fine particle size distribution. The high-voltage electrolyte with additive fluoroethylene carbonate (FEC) has been used. Electrochemical results show that the initial discharge capacities of the prepared LiCoO₂ cathode are 157.7, 169.5, 191.0, and 217.5 mAh g^?1 in the voltage ranges of 3.0–4.3, 3.0–4.4, 3.0–4.5, and 3.0–4.6 V, respectively. The capacity increases, while the initial coulombic efficiency and capacity retention decrease with increasing the charge cutoff voltage. The capacity retention is only 10.4 % after 200 cycles at 1C rate in the voltage range of 3.0–4.6 V. X-ray diffraction measurements confirm structural changes of the layered material in the different voltage ranges. A phase transition from the O3 to the H1-3 phase can be observed when LiCoO₂ is charged above 4.5 V. The AC impedance analysis indicates that the resistances (R _(sf+b), R _ct) of the prepared LiCoO₂ rapidly increase when the cell is charged to higher voltage. The amount of dissolved Co into the electrolyte also greatly increases with increasing the charge cutoff voltage.     

The preparation and electrochemical properties of the Li-excess cathode material Li1 + x (Mn0.7Fe0.3)1 − x O2 by coprecipitation method

The Fe-substituted Li₂MnO₃ cathode materials were synthesized by the coprecipitation method. The effects of the different precipitants of Na₂CO₃ and NaOH on the structure, morphology, and electrochemical performance were investigated by X-ray diffractometry, scanning electron microscopy, dQ/dV plots, and charge–discharge tests. The results indicate that the materials prepared using both precipitants possess layered α-NaFeO₂ structure with R-3m space group. However, the material prepared using Na₂CO₃ shows smaller primary particle size as well as higher discharge capacity. The cycling test shows that the initial discharge capacity is 206 mAh g^?1 in the voltage range of 2.5–4.8 V under current density of 30 mA g^?1 at 30 °C and 231 mAh g^?1 in the voltage range of 2.0–4.8 V. Meanwhile, the discharge capacity fades to 191 mAh g^?1 after 20 cycles. The activated Mn⁴⁺ was confirmed to contribute to the high reversible capacities.     

Modified carbothermal synthesis and electrochemical performance of LiFePO4/C composite as cathode materials for lithium-ion batteries

LiFePO₄/C active materials were synthesized via a modified carbothermal method, with a low raw material cost and comparatively simple synthesis process. Rheological phase technology was introduced to synthesize the precursor, which effectively decreased the calcination temperature and time. The LiFePO₄/C composite synthesized at 700 °C for 12 h exhibited an optimal performance, with a specific capacity about 130 mAh g^?1 at 0.2C, and 70 mAh g^?1 at 20C, respectively. It also showed an excellent capacity retention ratio of 96 % after 30 times charge–discharge cycles at 20C. EIS was applied to further analyze the effect of the synthesis process parameters. The as-synthesized LiFePO₄/C composite exhibited better high-rate performance as compared to the commercial LiFePO₄ product, which implied that the as-synthesized LiFePO₄/C composite was a promising candidate used in the batteries for applications in EVs and HEVs.     

Compatibility study of oxide and olivine cathode materials with lithium aluminum titanium phosphate

The compatibility of the solid electrolyte Li_1.5Al_0.5Ti_1.5(PO₄)₃ (LATP) with the cathode materials LiCoO₂, LiMn₂O₄, LiCoPO₄, LiFePO₄, and LiMn_0.5Fe_0.5PO₄ was investigated in a co-sintering study. Mixtures of LATP and the different cathode materials were sintered at various temperatures and subsequently analyzed by thermal analysis, X-ray diffraction, and electron microscopy. Oxide cathode materials display a rapid decomposition reaction with the electrolyte material even at temperatures as low as 500 °C, while olivine cathode materials are much more stable. The oxide cathode materials tend to decompose to lithium-free compounds, leaving lithium to form Li₃PO₄ and other metal phosphates. In contrast, the olivine cathode materials decompose to mixed phosphates, which can, in part, still be electrochemically active. Among the olivine cathode materials, LiFePO₄ demonstrated the most promising results. No secondary phases were detected by X-ray diffraction after sintering a LATP/LiFePO₄ mixture at temperatures as high as 700 °C. Electron microscopy revealed a small secondary phase probably consisting of Li₂FeTi(PO₄)₃, which is ionically conductive and should be electrochemically active as well.     

Dinitrile compound containing ethylene oxide moiety with enhanced solubility of lithium salts as electrolyte solvent for high-voltage lithium-ion batteries

A dinitrile compound containing ethylene oxide moiety (4,7-dioxa-1,10-decanedinitrile, NEON) is synthesized as an electrolyte solvent for high-voltage lithium-ion batteries. The introduction of ethylene oxide moiety into the conventional aprotic aliphatic dinitrile compounds improves the solubility of lithium hexafluorophosphate (LiPF₆) used commercially in the lithium-ion battery industry. The electrochemical performances of the NEON-based electrolyte (0.8 M LiPF₆?+?0.2 M lithium oxalyldifluoroborate in NEON:EC:DEC, v:v:v?=?1:1:1) are evaluated in graphite/Li, LiCoO₂/Li, and LiCoO₂/graphite cells. Half-cell tests show that the electrolyte exhibits significantly improved compatibility with graphite by the addition of vinylene carbonate and lithium oxalyldifluoroborate and excellent cycling stability with a capacity retention of 97 % after 50 cycles at a cutoff voltage of 4.4 V in LiCoO₂/Li cell. A comparative experiment in LiCoO₂/graphite full cells shows that the electrolyte (NEON:EC:DEC, v:v:v?=?1:1:1) exhibits improved cycling stability at 4.4 V compared with the electrolyte without NEON (EC:DEC, v:v?=?1:1), demonstrating that NEON has a great potential as an electrolyte solvent for the high-voltage application in lithium-ion batteries.     

Hierarchical nanostructure CuO with peach kernel-like morphology as anode material for lithium-ion batteries

Copper oxide particles with different morphology (flower-like, peach kernel-like, and dandelion-like) are prepared with hydrothermal method by adjusting chitosan ((C₆H₁₁NO₄)_n) concentration in aqueous mixed solutions of ammonia and Cu(NO₃)₂. Various morphologies of porous cupric oxide (CuO) particles are formed by agglomerated nanosheet primary particles and lead to different electrochemical performance of electrodes. The peach kernel-shaped CuO exhibits high reversible capacity and rate capability. The reversible capacity is 722.7 mAh g^?1 at 0.1 C in the first cycle and 339 mAh g^?1 after 50 cycles at 0.2, 0.5, 1.0, and 2.0 C ratio. The higher reversible capacities and good cycling performance are attributed to the larger specific surface area, leading to better contact between CuO and electrolyte.