KINETICS AND PHASE TRANSFORMATIONS DURING THE REACTION OF NaCl-SODALITE IN AMMONIUM CHLORIDE SOLUTIONS

The reaction behavior of sodium chloride sodalite Na₈[AlSiO₄]₆Cl₂ in ammonium chloride solution has been investigated under mild hydrothermal conditions (T = 473 K) for reaction times up to 72 h. Reactions under weak acid conditions led to an amorphous aluminosilicate phase comparable to a leaching process. This material forms an amorphous layer around the sodalite grains, preventing the framework from further decomposition. About 52% of sodalite was damaged by acid leaching after 11 hours and this amount remains nearly constant even at longer reaction periods up to 72 hours. Cation exchange was observed in sodalite only on a very low level (< 10%). Beside these reactions under acid conditions (pH » 5) some additional experiments in alkaline solutions were done to improve ion exchange of sodalite. Thus an ammonium/ammonia buffer solution was used (pH » 9) at various temperatures in a range of 353 – 473 K. Neither cation exchange nor decomposition of the sodalite was obtained at 353 and 393 K after 72 hours. Formation of amorphous material started at 433 K. In contrast to the acid conditions a total transformation of sodalite into a crystalline ammonium aluminosilicate phase was observed at 473 K.     

新合成方法制备的LiCoO2正极材料的结构和电化学性能研究

采用新合成方法制备了锂离子二次电池正极材料LiCoO₂。通过ICP-AES、XRD、SEM、电化学方法等测试分析了所合成材料的物理性质和电化学性能，并与商品LiCoO₂材料作了对比研究。同时分别以国产MCMB和石墨作负极活性物质、合成的LiCoO₂作正极活性物质做成锂离子电池，对其电化学性能进行了测试。实验结果表明，所合成的LiCoO₂材料的电化学性能优于其它两种商品LiCoO₂材料，其初始放电容量为155.0 mAh·g^-1，50次循环后的容量保持率达95.3%，而且以此为正极的锂离子电池也表现出优良的电化学性能。计时电位分析结果还表明，合成的材料在充放电循环过程中发生了三次相转变过程，但相变过程具有良好的可逆性。     

Structural and electrochemical characterization of polyaniline/LiCoO2 nanocomposites prepared via a Pickering emulsion

Polyaniline (PANI)/LiCoO₂ nanocomposite materials are successfully ready through a solid-stabilized emulsion (Pickering emulsion) route. The properties of nanocomposite materials have been put to the test because of their possible relevance to electrodes of lithium batteries. Such nanocomposite materials appear thanks to the polymerization of aniline in Pickering emulsion stabilized with LiCoO₂ particles. PANI has been produced through oxidative polymerization of aniline and ammonium persulfate in HCl solution. The nanocomposite materials of PANI/LiCoO₂ could be formed with low amounts of PANI. The morphology of PANI/LiCoO₂ nanocomposite materials shows nanofibers and round-shape-like morphology. It was found that the morphology of the resulting nanocomposites depended on the amount of LiCoO₂ used in the reaction system. Ammonium persulfate caused the loss of lithium from LiCoO₂ when it was used at high concentration in the polymerization recipe. Highly resolved splitting of 006/102 and 108/110 peaks in the XRD pattern provide evidence to well-ordered layered structure of the PANI/LiCoO₂ nanocomposite materials with high LiCoO₂ content. The ratios of the intensities of 003 and 104 peaks were found to be higher than 1.2 indicating no pronounced mixing of the lithium and cobalt cations. The electrochemical reactivity of PANI/LiCoO₂ nanocomposites as positive electrode in a lithium battery was examined during lithium ion deinsertion and insertion by galvanostatic charge–discharge testing; PANI/LiCoO₂ nanocomposite materials exhibited better electrochemical performance by increasing the reaction reversibility and capacity compared to that of the pristine LiCoO₂ cathode. The best advancement has been observed for the PANI/LiCoO₂ nanocomposite 5 wt.% of aniline.     

Olivine LiCoPO4 phase grown LiCoO2 cathode material for high density Li batteries

Olivine LiCoPO₄ phase grown LiCoO₂ cathode material was prepared by mixing precipitated Co₃(PO₄)₂ nanoparticles and LiCoO₂ powders in distilled water, followed by drying and annealing at 120 °C and 700 °C, respectively, for 5 h. As opposed to ZrO₂ or AlPO₄ coatings that showed a clearly distinguishable coating layer from the bulk materials, Co₃(PO₄)₂ nanoparticles were completely diffused into the surface of the LiCoO₂ and reacted with lithium of LiCoO₂. An olivine LiCoPO₄ phase was grown on the surface of the bulk LiCoO₂, with a thickness of ∼7 nm. The electrochemical properties of the LiCoPO₄ phase, grown in LiCoO₂, had excellent cycle life performance and higher working voltages at a 1C rate than the bare sample. More importantly, Li-ion cells, containing olivine LiCoPO₄, grown in LiCoO₂, showed only 10% swelling at 4.4 V, whereas those containing bare sample showed a 200% increase during storage at 90 °C for 5 h. In addition, nail penetration test results of the cell containing olivine LiCoPO₄, grown in LiCoO₂ at 4.4 V, did not exhibit thermal runaway with a cell surface temperature of ∼80 °C. However, the cell containing bare LiCoO₂ showed a burnt-off cell pouch with a temperature above 500 °C.     

Multifunctional Active-Center-Transferable Platinum/Lithium Cobalt Oxide Heterostructured Electrocatalysts towards Superior Water Splitting

Designing cost-effective and efficient electrocatalysts plays a pivotal role in advancing the development of electrochemical water splitting for hydrogen generation. Herein, multifunctional active-center-transferable heterostructured electrocatalysts, platinum/lithium cobalt oxide (Pt/LiCoO₂) composites with Pt nanoparticles (Pt NPs) anchored on LiCoO₂ nanosheets, are designed towards highly efficient water splitting. In this electrocatalyst system, the active center can be alternatively switched between Pt species and LiCoO₂ for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER), respectively. Specifically, Pt species are the active centers and LiCoO₂ acts as the co-catalyst for HER, whereas the active center transfers to LiCoO₂ and Pt turns into the co-catalyst for OER. The unique architecture of Pt/LiCoO₂ heterostructure provides abundant interfaces with favorable electronic structure and coordination environment towards optimal adsorption behavior of reaction intermediates. The 30 % Pt/LiCoO₂ heterostructured electrocatalyst delivers low overpotentials of 61 and 285 mV to achieve 10 mA cm⁻² for HER and OER in alkaline medium, respectively.     

Recycling Valuable Metals from Spent Lithium-Ion Batteries Using Carbothermal Shock Method

Pyrometallurgy technique is usually applied as a pretreatment to enhance the leaching efficiencies in the hydrometallurgy process for recovering valuable metals from spent lithium-ion batteries. However, traditional pyrometallurgy processes are energy and time consuming. Here, we report a carbothermal shock (CTS) method for reducing LiNi_0.3Co_0.2Mn_0.5O₂ (NCM325) cathode materials with uniform temperature distribution, high heating and cooling rates, high temperatures, and ultrafast reaction times. Li can be selectively leached through water leaching after CTS process with an efficiency of >90 %. Ni, Co, and Mn are recovered by dilute acid leaching with efficiencies >98 %. The CTS reduction strategy is feasible for various spent cathode materials, including NCM111, NCM523, NCM622, NCM811, LiCoO₂, and LiMn₂O₄. The CTS process, with its low energy consumption and potential scale application, provides an efficient and environmentally friendly way for recovering spent lithium-ion batteries.     

A novel carbon-coated LiCoO2 as cathode material for lithium ion battery

Using a commercially available LiCoO₂ as starting material, a surface-modified cathode material was obtained by coating it with a nano layer of amorphous carbon. The carbon-coated LiCoO₂ was characterized by X-ray diffraction analysis, scanning electronic microscopy, transmission electronic microscopy, electrochemical impedance spectroscopy and measurement of charge/discharge behavior. Results show that the carbon-coated LiCoO₂ displays marked lower charge transfer resistance, higher lithium ion diffusion coefficient and much better rate capability than the original LiCoO₂. It also indicates promising application of lithium ion batteries in the areas requiring charge and discharge at high rate.     

Multifunctional Active‐Center‐Transferable Platinum/Lithium Cobalt Oxide Heterostructured Electrocatalysts towards Superior Water Splitting

Designing cost‐effective and efficient electrocatalysts plays a pivotal role in advancing the development of electrochemical water splitting for hydrogen generation. Herein, multifunctional active‐center‐transferable heterostructured electrocatalysts, platinum/lithium cobalt oxide (Pt/LiCoO₂) composites with Pt nanoparticles (Pt NPs) anchored on LiCoO₂ nanosheets, are designed towards highly efficient water splitting. In this electrocatalyst system, the active center can be alternatively switched between Pt species and LiCoO₂ for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER), respectively. Specifically, Pt species are the active centers and LiCoO₂ acts as the co‐catalyst for HER, whereas the active center transfers to LiCoO₂ and Pt turns into the co‐catalyst for OER. The unique architecture of Pt/LiCoO₂ heterostructure provides abundant interfaces with favorable electronic structure and coordination environment towards optimal adsorption behavior of reaction intermediates. The 30 % Pt/LiCoO₂ heterostructured electrocatalyst delivers low overpotentials of 61 and 285 mV to achieve 10 mA cm^?2 for HER and OER in alkaline medium, respectively.     

Nano-encapsulation of LiCoO2 cathodes by a novel polymer electrolyte and its influence on thermal safeties of Li-ion batteries

A new approach enabling the target control of exothermic reaction between delithiated LiCoO₂ and liquid electrolytes has been presented, which is based on the nano-encapsulation of LiCoO₂ by cPVA (cyanoethyl polyvinylalcohol)-based gel polymer electrolytes. This novel morphology and the possible formation of coordinated complexes between the cyano (–CN) groups of cPVA and the cobalt cations of LiCoO₂ are considered as key factors to significantly suppress the exothermic reaction in the delithiated LiCoO₂. Such an improved thermal stability of the cPVA-modified LiCoO₂ has led to a noticeable achievement in the hot-oven safety behavior of cells. Meanwhile, it was observed that both the excellent ionic conductivity of cPVA-based gel polymer electrolytes and the well-preserved porous structure of modified cathodes contribute to the satisfactory C-rate capability and the cyclability of cells.     

球形钴酸锂的乳液法合成及其结构、性能研究

采用一种特殊乳液法, 制备了锂离子电池正极材料球形LiCoO₂. 分别研究了一次颗粒尺寸、烧结时间对于二次造粒的影响. 还对LiCoO₂球体内部的结构进行了SEM和HRTEM研究, 发现一次颗粒非常紧密地融合在一起, 晶体边界区域没有明显的非晶相区, 也没有纳米级别的孔洞、裂缝. 电化学性能研究表明, 在900 ℃烧结4 h的材料具有较高的首次放电容量(143 mAh•g^－1)和良好的循环性能     

Polyimide gel polymer electrolyte-nanoencapsulated LiCoO2 cathode materials for high-voltage Li-ion batteries

We demonstrate a novel and facile approach to surface modification of high-voltage charged LiCoO₂, which is based on encapsulating LiCoO₂ by a polyimide (PI) gel polymer electrolyte layer. The PI is introduced onto the LiCoO₂ by thermally curing 4-component (pyromellitic dianhydride/biphenyl dianhydride/phenylenediamine/oxydianiline) polyamic acid. The PI nanoencapsulating layer features the high surface coverage, nanometer thickness, and facile ion transport. These unique characteristics are expected to enable the PI coating layer to effectively suppress the undesirable interfacial reaction of the LiCoO₂ with liquid electrolyte, which plays a key role in noticeably improving the 4.4 V cycle performance and mitigating the vigorous exothermic reaction between the charged LiCoO₂ and liquid electrolyte.     

Structure Recovery and Recycling of Used LiCoO2 Cathode Material

A large number of lithium batteries have been retiring from the market of energy storage. Thus, recycling of the used electrode materials is becoming urgent. In this study, an industrial machinery processing was used to recover the crystal structure of the waste LiCoO₂ materials with the combination of small-scale equipment repair technology. The results show that the crystal parameters of the repaired LiCoO₂ material become small, the unit cell volume is reduced, and the crystal structure tends to be stable. The Co−O bond length of 1.9134 nm, O−Co−O bond angle of 94.72°, the (003) interplanar spacing of 0.467 nm indicate the excellent recovery level of the repaired LiCoO₂. In addition, the electrochemical performance of the repaired LiCoO₂ material is greatly improved, compared with the waste material. The capacity of the repaired electrode material can be maintained at 120 mAh g⁻¹ after 100 cycles at the current density of 0.2C. The promising rate performance of the repaired electrode material demonstrates the stable structure. This research work provides a large-scale method for the direct recovery of LiCoO₂ with the reduction of unnecessary energy and reagent consumption, which will be beneficial to the environmental protection.     

Influence of the PVdF binder on the stability of LiCoO2 electrodes

We report herein on the effect of the PVdF binder on the stability of composite LiCoO₂ electrodes at elevated temperatures in 1 M LiPF₆ EC/EMC solutions at open circuit conditions. The structure and morphology of composite LiCoO₂ electrodes with different combinations of electrode components (LiCoO₂ active material, PVdF binder, carbon black and current collector) were evaluated by Raman spectroscopy, X-ray diffraction and SEM. The content of Co ions in the electrolyte solutions was determined by ICP. A new effect was discovered, namely, a detrimental impact of the contact between PVdF and LiCoO₂ on the stability of the active mass. The formation of surface Co₃O₄ and dissolution of Co ions at elevated temperatures is accelerated at the contact points between the active mass and the binder. The effect of water content in the electrolyte solutions on the stability of LiCoO₂ was also studied. The presence of water (and/or HF) is a necessary condition for the accelerated dissolution of Co ions from the active mass. LiCoO₂ oxidizes the solvents at elevated temperatures thus forming CO₂.     

Thermal study of organic electrolytes with fully charged cathodic materials of lithium-ion batteries

We systematically investigated thermal effects of organic electrolytes/organic solvents with fully charged cathodic materials (Li_0.5CoO₂) of Li-ion battery under rupture conditions by using oxygen bomb calorimeter. In the six studied systems, both the amount of combustion heat and heat release rates showed a pronounced increase with the increase in mass ratios of cathodic materials to electrolytes/solvents. More importantly, synergistic effects not simply physical mixtures have firstly been observed between cathodic materials and electrolytes/solvents in the complete combustion reactions. The results have been further analyzed by X-ray diffraction spectra, which revealed that Co₃O₄, CoO, and LiCoO₂ were the main solid products for the combustion reactions of studied systems. And there are more CoO and less LiCoO₂ products for the higher ratio of cathodic materials system and more amount of heat generated. It means that the combustion reaction, which produced CoO, generated more amount of heat than LiCoO₂. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Effect of Mg doping and MgO-surface modification on the cycling stability of LiCoO2 electrodes

Two synthetic routes including Mg doping and MgO-surface modification were applied to the preparation of LiCoO₂ showing enhanced reversible cycling behaviour as cathode material in lithium ion batteries. Mg-doped LiCoO₂ was obtained by the citrate precursor method in the temperature range 750–900°C. The surface of LiCoO₂ was modified by coating with Mg(CH₃COO)₂ and subsequent heating at 600°C. XRD, chemical oxidative analysis and electron paramagnetic resonance (EPR) of Ni³⁺ spin probes were used to characterize the Mg distribution in LiCoO₂. Substitution of Co by Mg in the CoO₂-layers was found to have a positive effect on the cycling stability, while Mg dopants in LiO₂-layers did not influence the capacity fade. The accumulation of MgO on the surface of LiCoO₂ improves the cycling stability without loss of initial capacity.     

双包覆法改善高压钴酸锂正极材料的电化学性能

通过结合固相和液相包覆在Al掺杂LiCoO₂表面共包覆了钛酸锂（Li₄Ti₅O₁₂）和聚吡咯（PPy）。这种双包覆方法不仅稳定了高电压下LiCoO₂的表面,还增强了材料的离子和电子电导率。电化学测试表明,当活性物质、导电剂和黏结剂的质量比为80∶ 10∶10时,在0.5C （1C=180 mA·g^-1）电流下,循环300周后的容量保持率为76.9%,且在5C电流密度下可逆比容量为150 mAh· g^-1;由于双包覆后LiCoO₂电子电导率大幅提高,当活性物质、导电剂和黏结剂的质量比为90∶3∶7时,在0.5C电流下,循环200周后的容量保持率为82.8%,且在5C电流密度下可逆比容量为130 mAh·g^-1。X射线光电子能谱测试表明,包覆层可以在循环中保持稳定且能抑制LiCoO₂材料在高电压下的表面副反应。     

Preparation of nano-sized LiCoO2 powder by the combination of sonication and modified Pechini process

A sonication (ultrasonic processing) and modified Pechini process were combined to fabricate nano-sized LiCoO₂ powder. A composition of precursor solution for fabricating LiCoO₂ was modulated by controlling the molar ratios of lithium acetate to cobalt acetate and ethylene glycol to citric acid, respectively. The sonication was applied on the precursor solution to get highly dispersed transition-metal oxide powder. The sonicated precursor gels pre-dried were calcined in the range of 400 to 800 °C for 10 h. Effect of sonication on the particle size and the morphology of LiCoO₂ prepared by the modified Pechini process was elucidated. After calcination, the unsonicated LiCoO₂ powder had an aggregated-like morphology, as combined loosely and/or firmly, while the sonicated LiCoO₂ was more ultra-finely particulated and presented more mono-dispersed morphology without severe aggregation. The nano-sized LiCoO₂ with high crystallinity and homogeneity could be prepared by the combination of sonication and modified Pechini process.     

LiCoO2对LiMn2O4改性过程的研究

在LiCoO2、LiMn2O4、LiNiO2这三种锂离子电池正极材料中,尖晶石LiMn2O4由于具有价廉、对环境友好、使用安全的显著优点,被普遍认为是最有希望的新型正极材料。但该材料在高温下较快的容量衰减制约了其规模应用[1~3]。为改善LiMn2O4的高温性能,各国学者普遍采用掺杂法,即在制备L     

LiCoO2梯度包覆LiNi0.96Co0.04O2电极材料的电化学性能

镍钴酸锂(LiNi0.8Co0.2O2)与目前商业用锂离子电池正极材料钴酸锂(LiCoO2)相比,具有成本低、实际比容量高和环境友好等优势。但LiNi0.8Co0.2O2的充放循环性能还有待提高,对其进行阳离子掺杂或表面修饰可以改善其电化学性能,这方面的研究已经成为热点。Fey等人[1]用溶胶凝胶法制     

Magnetic phase transition of Li0.75CoO2 compared with LiCoO2 and Li0.5CoO2

Magnetic and thermodynamic properties of the LiCoO₂ positive-electrode material used in lithium-ion battery were first examined. Partially deintercalated LiCoO₂ that is Li_0.75CoO₂, showed definite anomaly in the magnetic susceptibility at T=ca. 175 K probably related to magnetic phase transition which was supported by observation of a weak anomaly in heat capacity. On the other hand, LiCoO₂ did not show such magnetic phase transition as expected, whereas Li_0.5CoO₂ a weak one in the similar temperature range. These behaviors are discussed in association with the mixing of Co³⁺ and Co⁴⁺ electronic structures.