Experimental Investigation and Thermodynamic Modeling of LNMO High Voltage Spinel Cathode for the LIBs

高压Li- ni - mn - o （LNMO，化学计量成分LiNi0.5Mn1.5O4, 4.7 V vs. Li）尖晶石具有高能量密度，是非常有前途的锂离子电池正极材料。基于这些新材料的lib电源和热管理系统的设计迫切需要一致的热化学和电化学数据。尽管已经发表了许多关于电池性质的研究，但热化学（生成焓、热容）和电化学数据（充放电过程中的反应熵）却很少。因此，本项目的目的是研究LNMO尖晶石的热化学和电化学，并利用这些结果首次建立各自相的吉布斯自由能的自一致分析描述。本文的实验研究包括采用溶胶-凝胶法合成具有选定阳离子比的尖晶石样品。在规定的气氛下进行热处理可获得不同氧空位浓度的样品。采用粉末xrd， ICP-OES和SEM对样品进行表征。氧化还原滴定技术将被用来确定Mn阳离子的平均氧化状态，允许计算氧空位浓度。此外，生成焓将使用滴液量热法测量，热容测量将使用不同的DSC设备进行。电池测试电池（硬币电池，世伟洛克电池）将与尖晶石阴极组装在纯锂上，并将用于电位测定研究，以获得锂化-去锂化过程中的熵变化。本文将研究LMO和LNMO尖晶石的组成。基于Calphad方法的实验数据，将晶体结构和Wyckoff点占位率（氧空位浓度、阳离子混合）考虑在内，建立一个模型。通过对吉布斯能量和正确亚晶格位置占用之间的关系进行建模，首次模拟了锂化-剥蚀过程。在不同条件下，将对电池的行为进行预测，包括开路电压、产热特性和氧分压与温度的相关性。作为本次项目的产出，将根据热力学计算提出提高电池性能的LNMO尖晶石的合成条件。同时，所获得的热力学模型将对具有新型尖晶石阴极材料的锂离子电池的ICME开发起到关键作用。此外，热化学信息对于电池的安全性和防止热失控和火焰产生等危险现象至关重要。

High voltage Li-Ni-Mn-O (LNMO, stoichiometric composition LiNi0.5Mn1.5O4, 4.7 V vs. Li) spinels are very promising cathode materials for Li-ion batteries (LIBs) due to the high energy densities. Consistent thermochemical and electrochemical data are urgently required for the design of power and thermal management systems of LIBs based on these new materials. Although numerous cell property investigations have been published, thermochemical (enthalpy of formation, heat capacity) and electrochemical data (entropy of reaction during charge-discharge processes) are rare. Therefore, the aim of this project is to investigate the thermochemistry and electrochemistry of LNMO spinels and to use the results to develop self-consistent analytical descriptions of the Gibbs free energy of the respective phases for the first time.The experimental studies in this proposal include the synthesis of spinel samples with selected cation ratios using the sol-gel method. Heat treatments in defined atmospheres will be used to obtain samples with different oxygen vacancy concentrations. Sample characterization will be performed using powder-XRD, ICP-OES and SEM. Redox titration techniques will be employed to determine the average oxidation state of Mn cations, allowing the calculation of oxygen vacancy concentrations. Moreover, enthalpies of formation will be measured using drop solution calorimetry, and heat capacity measurements will be conducted using different DSC devices. Battery test cells (Coin cells, Swagelok cells) will be assembled with the spinel cathode against pure Li, and will be used for potentiometric investigation to obtain the entropy changes during lithiation-delithiation process. Both LMO and LNMO spinels compositions will be investigated.A model taking the crystal structure and Wyckoff site occupancies into account (oxygen vacancy concentrations, cation mixing), will be established based on the experimental data using the Calphad approach. Lithiation-delithiation process will be simulated by modeling the relation between Gibbs energy and correct sublattice site occupations for the first time. Predictions of battery behaviors including open circuit voltages, heat generation properties, and oxygen partial pressures with temperature dependencies under varying conditions, will be performed.As the output of the current project, conditions for synthesizing LNMO spinel with improved battery performance will be proposed according to thermodynamic calculations. Meanwhile, the obtained thermodynamic models will be key contributors to the ICME development of LIBs with novel spinel cathode materials. Furthermore, the thermochemical information is essential for the battery safety and preventing hazardous phenomena such as thermal runaway and flame generation.