Cr3+掺杂LiNi0.5Mn1.5O4材料的制备及性能研究

采用高温固相法合成了Cr₃₊掺杂的LiNi_0.5Mn_1.5O₄正极材料,研究了掺杂量对材料物理性能和电化学性能的影响。利用XRD、SEM对材料的结构和形貌进行了表征,结果显示样品具有棱边清晰的尖晶石形貌。讨论了不同Cr₃₊掺杂量对LiCr_xNi_0.5-0.5xMn_1.5-0.5xO₄(x=0,0.05,0.1,0.15,0.2)正极材料性能的影响。充放电测试、循环伏安和交流阻抗测试结果表明：当Cr₃₊的掺杂量为x=0.1时(LiCr_0.1Ni_0.45Mn_1.45O₄)正极材料的性能最好,0.1C、0.5C、1C、2C及5C的首次放电比容量依次为131.54mAh g_-1、126.84mAh g_-1、121.28mAh g_-1、116.49mAh g_-1和96.82mAh g_-1,1C倍率下循环50次,容量保持率仍为96.5%。     

Effect of the impurity LixNi1−xO on the electrochemical properties of 5 V cathode material LiNi0.5Mn1.5O4

The formation of impurity Li_xNi_1−xO when synthesizing spinel LiNi_0.5Mn_1.5O₄ using solid state reaction method, and its influence on the electrochemical properties of product LiNi_0.5Mn_1.5O₄ were studied. The secondary phase Li_xNi_1−xO emerges at high temperature due to oxygen deficiency for LiNi_0.5Mn_1.5O₄ and partial reduction of Mn⁴⁺ to Mn³⁺ in LiNi_0.5Mn_1.5O₄. Annealing process can diminish oxygen deficiency and inhibit impurity Li_xNi_1−xO. The impurity reduces the specific capacity of product, but it does not have obvious negative effect on cycle performance of product. The capacity of LiNi_0.5Mn_1.5O₄ that contains Li_xNi_1−xO can deliver about 120 mAh g⁻¹.     

Study of synthesis and electrochemical properties of spinel LiNi0.5Mn1.2Ti0.3O4 by different methods

Two spinel LiNi_0.5Mn_1.2Ti_0.3O₄ samples were successfully synthesized by the sol-gel method using chemicals LiAc·2H₂O, Mn(Ac)₂·2H₂O, Ni(Ac)₂·4H₂O and Ti(OCH₃)₄ as reactants. When reactants are calcined in air, a sample of LiNi_0.5Mn_1.2Ti_0.3O₄ (1), which contains Mn³⁺ and Mn⁴⁺ ions, is obtained. The sample of LiNi_0.5 Mn_1.2Ti_0.3O₄ (2), which contains only Mn⁴⁺ ions, is obtained when reactants are calcined in an oxygen atmosphere. X-ray diffraction (XRD), scanning electron microscopy (SEM), galvanostatic charge-discharge test and cyclic voltammogram test were employed to investigate the two samples. XRD results show that there is a small shift towards a larger diffraction angle for peaks of the LiNi_0.5Mn_1.2Ti_0.3O₄ (2) sample. SEM indicates that the two samples exhibit polyhedral shapes. The cyclic voltammogram test demonstrates that reduction-oxidation reactions take place at different voltages for the two samples. The prepared sample of LiNi_0.5Mn_1.2Ti_0.3O₄ with Mn³⁺ ions exhibits excellent cycle performance at different current rates. Its discharge capacity is 133.9 mAh/g at 0.1C.     

Sol-gel synthesis and electrochemical performance of Li4Ti5O12/graphene composite anode for lithium-ion batteries

Li₄Ti₅O₁₂/graphene composite was prepared by a facile sol-gel method. The lattice structure and morphology of the composite were investigated by X-ray diffraction (XRD) and scanning electronic microscopy (SEM). The electrochemical performances of the electrodes have been investigated compared with the pristine Li₄Ti₅O₁₂ synthesized by a similar route. The Li₄Ti₅O₁₂/graphene composite presents a higher capacity and better cycling performance than Li₄Ti₅O₁₂ at the cutoff of 2.5-1.0 V, especially at high current rate. The excellent electrochemical performance of Li₄Ti₅O₁₂/graphene electrode could be attributed to the improvement of electronic conductivity from the graphene sheets. When discharged to 0 V, the Li₄Ti₅O₁₂/graphene composite exhibited a quite high capacity over 274 mAh g⁻¹ below 1.0 V, which was quite beneficial for not only the high energy density but also the safety characteristic of lithium-ion batteries.     

Improved capacity and rate capability of Ru-doped and carbon-coated Li4Ti5O12 anode material

Pure Li₄Ti₅O₁₂, modified Li₄Ti₅O₁₂/C, Li₄Ru_0.01Ti_4.99O₁₂ and Li₄Ru_0.01Ti_4.99O₁₂/C were successfully prepared by a modified solid-state method and its electrochemical properties were investigated. From the XRD patterns, the added sugar or doped Ru did not affect the spinel structure. The results of electrochemical properties revealed that Li₄Ru_0.01Ti_4.99O₁₂/C showed 120 and 110 mAh/g at 5 and 10 C rate after 100 charge/discharge cycles. Li₄Ru_0.01Ti_4.99O₁₂/C exhibited the best rate capability and the highest capacity at 5 and 10 C charge/discharge rate owing to the increase of electronic conductivity and the reduction of interface resistance between particles of Li₄Ti₅O₁₂.It is expected that the Li₄Ru_0.01Ti_4.99O₁₂/C will be a promising anode material to be used in high-rate lithium ion battery.     

A facile method to prepare hybrid LiNi0.5Mn1.5O4/C with enhanced rate performance

The hybrid LiNi_0.5Mn_1.5O₄/C cathode material is prepared with a facile method of pre-mixing and post-calcination treatment for enhancing the rate performance. The physical and electrochemical properties are discussed through X-ray diffraction (XRD), transmission electron microscopy (TEM), charge-discharge measurements in test cells and electrochemical impedance spectroscopy (EIS). The results show that the LiNi_0.5Mn_1.5O₄ particle can be partially surrounded and interconnected with each other by carbon black particles, therefore the electronic conductivity can be remarkably improved by over 5 times without degrading the spinel structure. The LiNi_0.5Mn_1.5O₄/C composite exhibits enhanced rate capability together with cycling performance compared to LiNi_0.5Mn_1.5O₄. EIS confirms that the significantly improved electrochemical property is due to the suppression of surface resistance and the enhanced electronic conductivity.     

Characterization and electrochemical properties of carbon-coated Li4Ti5O12 prepared by a citric acid sol-gel method

Since carbon coating can effectively improve electrical wiring of Li₄Ti₅O₁₂ and thus enhance its high rate performance, a novel and simple citric acid sol-gel method for in situ carbon coating is employed in this study. The effects of the amount of the carbon source in the starting xerogel on the particle size, the resistance and the electrochemical performance of the synthesized Li₄Ti₅O₁₂ samples are systematically studied. The physical and electrochemical properties of the obtained samples have been characterized by XRD, TG-DSC, SEM, TEM, BET, A.C. impedance, galvanostatically charge-discharge and cyclic voltammetry tests. The results show that the initial amount of the carbon source in the starting xerogel is a critical factor which determines the content of the coated carbon and the pore volume, therefore governs the high rate performance of the Li₄Ti₅O₁₂/C composites. The Li₄Ti₅O₁₂/C composite with in situ carbon coating of 3.5 wt% exhibits the best electrochemical performance which delivers delithiation capacities of 143.6 and 133.5 mAh g⁻¹ with fairly stable cycling performance even after 50 cycles at 0.5C and 1C rate, respectively.     

Porous Li4Ti5O12 anode material synthesized by one-step solid state method for electrochemical properties enhancement

A porous Li₄Ti₅O₁₂ anode material was successfully synthesized from mixture of LiCl and TiCl₄ with 70 wt% oxalic acid by a modified one-step solid state method. The anode material Li₄Ti₅O₁₂ exhibited a cubic spinel structure and only one voltage plateau occurred around 1.5 V. The initial capacity of porous Li₄Ti₅O₁₂ was 167 and 133 mAh g⁻¹ at 0.5 and 1C charge/discharge rate, respectively, and the capacity retention maintained above 98% after 200 cycles. The porous Li₄Ti₅O₁₂ structure showed promising rate performance with a capacity of 70 mAh g⁻¹ at charge/discharge 10C rate after 200 cycles. It was demonstrated that the porous structure could withstand 50C charge/discharge rate and exhibited excellent cycling stability.     

Preparation and characterization of spinel Li4Ti5O12 anode material from industrial titanyl sulfate solution

Spinel Li₄Ti₅O₁₂ anode material is successfully synthesized by a solid-state method using lithium carbonate and titanium precursors which are prepared by the low cost industrial titanyl sulfate solution. The characters of H₂TiO₃ and TiO₂ precursors are determined by TG/DTA and SEM methods. TG-DAT and EDS methods show that H₂TiO₃ can absorb sulphate ions which can be present as impurities. XRD method shows that the impure phases of Li₂SO₄ and rutile TiO₂ appear in Li₄Ti₅O₁₂ synthesized by H₂TiO₃. The formation of Li₂SO₄ is identified in thermodynamics during the process of calcination. Owing to the formation of Li₂SO₄ impurity, the capacity of the Li₄Ti₅O₁₂ synthesized by H₂TiO₃ is low. One effective way that can tackle this problem is to remove the sulphur by calcining H₂TiO₃, after calcinations, the production will have a thermal treatment with Li₂CO₃. The obtained Li₄Ti₅O₁₂ shows better electrochemical performance. The specific capacities can be increased by 20 mAh g⁻¹ at 0.1, 0.5 and 1C rates.     

基于碳纳米管宏观膜的高比容量及高电化学稳定性钛酸锂负极

通过对预先将钛酸锂(Li₄Ti₅O₁₂,LTO)材料组装的电池进行预充电脱锂(活化)的方式改变其结构,增强嵌锂能力,制备出高比容量Li₄Ti₅O₁₂;然后以CMF(碳纳米管宏观膜)为集流体,替代金属箔集流体改善活性物质与集流体的结合界面,提高其电化学稳定性,最终得到具有高比容量及高稳定性的LTO电极。采用X射线衍射(XRD)、扫描电子显微镜(SEM)和电化学测试等表征技术进行表征。结果表明：经过预脱锂活化后的LTO可容纳锂离子的空位增加,晶面间距发生显著的增大,经测试其在1C倍率能发挥192.7 mAh/g的比容量,比正常的Li₄Ti₅O₁₂材料提高约30 mAh/g;引入的CMF集流体能增强与活性材料的结合力,减小其在大电流下产生的接触阻抗,使其在5C倍率下仍具有150 mAh/g的比容量,表现出优异的倍率性能。     

Synthesis and electrochemical properties of Li4Ti5O12

The spinel compound Li₄Ti₅O₁₂ was synthesized by a solid state method. In this synthesizing process, anatase TiO₂ and Li₂CO₃ were used as reactants. The influences of reaction temperature and calcination time on the properties of products were studied. When calcination temperature was 750 °C and calcination temperature was 24 h, the products exhibited good electrochemical properties. Its discharge capacity reached 160 mAh g⁻¹ and its capacity retention was 97% at the 50th cycle when the current rate was 1 C. When current rate increased to 10 C, its first discharge capacity could reach 136 mAh g⁻¹, and its capacity retention was 85% at the 50th cycle.     

Electrochemical properties of spinel compound LiNi_（0.5）Mn_（1.2）Ti_（0.3）O_4 as cathode materials for lithium ion batteries

The electrochemical properties of spinel compound LiNi0.5Mn1.2Ti0.3O4 were investigated in this study.The chemicals LiAc·2H2O,Mn(Ac)2·2H2O,Ni(Ac)2·4H2O,and Ti(OCH3)4 were used to synthesize LiNi0.5Mn1.2Ti0.3O4 by a simple sol-gel method.The discharge capacity of the sample reached 134 mAh/g at a current rate of 0.1C.The first and fifth cycle voltammogram almost overlapped,which showed that the prepared sample LiNi0.5Mn1.2Ti0.3O4 had excellent good cycle performance.There were two oxidation peaks at 4.21 V and 4.86 V,and two reduction peaks at 4.55 V and 3.88 V in the cycle voltammogram,respectively.By electrochemical impedance spectroscopy and its fitted result,the lithium ion diffusion coefficient was measured to be approximately 7.76 × 10?11 cm2/s.     

Surface modification of LiNi<Subscript>1/3</Subscript>Co<Subscript>1/3</Subscript>Mn<Subscript>1/3</Subscript>O<Subscript>2</Subscript> with Cr<Subscript>2</Subscript>O<Subscript>3</Subscript> for lithium ion batteries

Cr 2 O 3-coated LiNi 1/3 Co 1/3 Mn 1/3 O 2 cathode materials were synthesized by a novel method. The structure and electrochemical properties of prepared cathode materials were measured using X-ray diffraction (XRD), scanning electron microscopy (SEM), charge-discharge tests, cyclic voltammetry (CV), and electrochemical impedance spectroscopy (EIS). The measured results indicate that surface coating with 1.0 wt% Cr 2 O 3 does not affect the LiNi 1/3 Co 1/3 Mn 1/3 O 2 crystal structure (α-NaFeO 2 ) of the cathode material compared to the pristine material, the surfaces of LiNi 1/3 Co 1/3 Mn 1/3 O 2 samples are covered with Cr 2 O 3 well, and the LiNi 1/3 Co 1/3 Mn 1/3 O 2 material coated with Cr 2 O 3 has better electrochemical performance under a high cutoff voltage of 4.5 V. Moreover, at room temperature, the initial discharging capacity of LiNi 1/3 Co 1/3 Mn 1/3 O 2 material coated with 1.0 wt.% Cr 2 O 3 at 0.5C reaches 169 mAh·g 1 and the capacity retention is 83.1% after 30 cycles, while that of the bare LiNi 1/3 Co 1/3 Mn 1/3 O 2 is only 160.8 mAh·g 1 and 72.5%. Finally, the coated samples are found to display the improved electrochemical performance, which is mainly attributed to the suppression of the charge-transfer resistance at the interface between the cathode and the electrolyte.     

Synthesis and electrochemical performance of Li(Ni0.8Co0.15Al0.05)0.8(Ni0.5Mn0.5)0.2O2 with core-shell structure as cathode material for Li-ion batteries

The core-shell structure cathode material Li(Ni_0.8Co_0.15Al_0.05)_0.8(Ni_0.5Mn_0.5)_0.2O₂ (LNCANMO) was synthesized via a co-precipitation method. Its applicability as a cathode material for lithium ion batteries was investigated. The core-shell particle consists of LiNi_0.8Co_0.15Al_0.05O₂ (LNCAO) as the core and a LiNi_0.5Mn_0.5O₂ as the shell. The thickness of the LiNi_0.5Mn_0.5O₂ layer is approximately 1.25 μm, as estimated by field emission scanning electron microscopy (FE-SEM). The cycling behavior between 2.8 and 4.3 V at a current rate of 18 mA g⁻¹ shows a reversible capacity of about 195 mAh g⁻¹ with little capacity loss after 50 cycles. High-rate capability testing shows that even at a rate of 5 C, a stable capacity of approximately 127 mAh g⁻¹ is retained. In contrast, the capacity of LNCAO rapidly decreases in cyclic and high rate tests. The observed higher current rate capability and cycle stability of LNCANMO can be attributed to the lower impedance including charge transfer resistance and surface film resistance. Differential scanning calorimetry (DSC) indicates that LNCANMO had a much improved oxygen evolution onset temperature of approximately 251 °C, and a much lower level of exothermic-heat release compared to LNCAO. The improved thermal stability of the LNCANMO can be ascribed to the thermally stable outer shell of LiNi_0.5Mn_0.5O₂, which suppresses oxygen release from the host lattice and not directly come into contact with the electrolyte solution. In particular, LNCANMO is shown to exhibit improved electrochemical performance and is a safe material for use as an electrode for lithium ion batteries.     

Mn3O4 doped with nano-NaBiO3: A high capacity cathode material for alkaline secondary batteries

In this paper we report a novel Mn₃O₄ electrode doped with nano-NaBiO₃. It is demonstrated that doping with nano-NaBiO₃ alters the electrochemical inertia of Mn₃O₄, converting it into a rechargeable secondary alkaline cathode material that exhibits highly efficient charge/discharge properties. While a pure Mn₃O₄ electrode can barely maintain a single charge and discharge cycle, the cycling capacity of the Mn₃O₄ electrode doped with nano-NaBiO₃ can reach and become stable at 372 mAh g⁻¹ under 60 mA g⁻¹. The doped cathode can also maintain a cycling capacity of 261 mAh g⁻¹ while holding a 95.3% reversible capacity after 60 cycles at a high rate of 500 mA g⁻¹. Moreover, the experimental results indicate that charging time for an alkaline battery using doped Mn₃O₄ cathode could possibly shorten to as little as 30 min.     

Effects of synthesis conditions on the structural and electrochemical properties of layered LiNi1/3Co1/3Mn1/3O2 cathode material via oxalate co-precipitation method

The uniform layered LiNi_1/3Co_1/3Mn_1/3O₂ cathode material for lithium ion batteries was prepared by using (Ni_1/3Co_1/3Mn_1/3)C₂O₄ as precursor synthesized via oxalate co-precipitation method in air. The effects of calcination temperature and time on the structure and electrochemical properties of the LiNi_1/3Co_1/3Mn_1/3O₂ were systemically studied. XRD results revealed that the optimal calcination conditions to prepare the layered LiNi_1/3Co_1/3Mn_1/3O₂ were 950°C for 15 h. Electrochemical measurement showed that the sample prepared under the such conditions has the highest initial discharge capacity of 160.8 mAh/g and the smallest irreversible capacity loss of 13.5% as well as stable cycling performance at a constant current density of 30 mA/g between 2.5 and 4.3 V versus Li at room temperature.     

The distinct role of transition metal doping for LiFePO<Subscript>4</Subscript> cathode material

This study addresses the controversial issue of the effect of metal ion doping on the electrochemical performance of LiFePO₄. Metal doping is claimed to be a possible cause for the capacity improvement of LiFePO₄ as carbon coating. Results obtained inthis study show that dry-milled LiFePO₄ and LiFe_0.9Cr_0.1PO₄ deliver 119 mAh g⁻¹ and 101 mAh g⁻¹, while wet-milled LiFePO₄ and LiFe_0.9Cr_0.1PO₄ deliver 149 mAh g⁻¹ and 138 mAh g⁻¹, respectively. This indicates that the capacity improvement by metal doping is due to the carbonaceous materials produced during fabrication and not by the enhancement of ion diffusion. On the other hand, cycle test results show that metal doping enhances the rate capability at high C-rates by accelerating lithium ion diffusion.     

Structural characterization of layered LiNi0.85−xMnxCo0.15O2 with x = 0, 0.1, 0.2 and 0.4 oxide electrodes for Li batteries

We report the synthesis of LiNi_0.85−xCo_0.15Mn_xO₂ positive electrode materials from Ni_0.85−xCo_0.15Mn_x(OH)₂ and Li₂CO₃. XRD and XPS are used to study the effect of Mn-doping on the microstructures and oxidation states of the LiNi_0.85−xCo_0.15Mn_xO₂ materials. The analysis shows that Mn-doping promotes the formation of a single phase. With increasing substitution of Mn ions for Ni ions, the lattice parameter a decreases, while the lattice parameters c and c/a increase. XPS revealed that the oxidation states of Ni, Co and Mn in LiNi_0.85−xCo_0.15Mn_xO₂ compounds (where x = 0.1, 0.2 and 0.4) were +2/+3, +3 and +4. The substitution of Mn ions for Ni ions induces a decrease in the average oxidation state of Ni. Because the substitution of Mn for Ni ions is complex, the extent of the changes between the lattice parameter and L_M-O differ. The occupation of Ni in Li sites is affected by the ordering of Mn⁴⁺ with Ni²⁺ and Mn⁴⁺ with Li⁺.     

锂离子占位情况对钛酸锂结构及性能的影响

Li₄Ti₅O₁₂在快速充放电条件下具有优异的结构稳定性和高安全性,使其受到新能源汽车和储能领域的青睐。大量的研究人员已经对钛酸锂的锂离子插层过程进行了研究,研究表明放电过程中外界和位于8a位的锂离子全部转移到16c位,钛酸锂的容量受限于参与其中晶格位点和可逆锂离子的数量。然而,钛酸锂晶胞结构表明可容纳锂离子的晶格位点不止于此。锂离子可能取代Ti原子占据八面体16d位点,位于四面体48f位点,重新占据相变后空出的四面体的8a位点。本文主要综述了在Li₄Ti₅O₁₂的制备过程或成品中,通过化学或电化学方法处理后,LTO中锂离子占位情况与传统认知发生的改变及其这种变化带来的影响。同时,本文对这种变化和影响之间的内在机理展开了讨论和分析。