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

高电压Li-Ni-Mn-O（LNMO，化学计量组成LiNi0.5Mn1.5O4，相对于Li为4.7V）尖晶石由于高能量密度而非常有希望用于锂离子电池（LIB）的阴极材料。一致的热化学和电化学数据的LIB的电源和热管理系统的设计迫切需要基于这些新材料。虽然已经发表了大量的电池性能研究，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）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开发出各自相的吉布斯自由能的自洽分析描述。本提案的实验研究包括使用溶胶-凝胶法合成具有选定阳离子比例的尖晶石样品。在规定的气氛中进行热处理将用于获得具有不同氧空位浓度的样品。将使用粉末XRD、ICP-OES和SEM进行样品表征。将采用氧化还原滴定技术测定Mn阳离子的平均氧化态，从而计算氧空位浓度。此外，将使用滴液量热法测量形成的结晶度，并使用不同的DSC装置进行热容测量。电池测试电池（纽扣电池，世伟洛克电池）将与尖晶石阴极组装在一起，以纯锂为对照，并将用于电位测量研究，以获得锂化-脱锂过程中的熵变化。对LMO和LNMO尖晶石的组成进行了研究，并基于实验数据，采用Calphad方法建立了一个考虑晶体结构和维科夫位占位（氧空位浓度、阳离子混合）的模型。首次通过建立吉布斯自由能与正确的亚晶格占位之间的关系，模拟锂化-脱锂过程。本项目将预测各种条件下的开路电压、发热特性、氧分压等电池行为，并根据热力学计算，提出合成LNMO尖晶石的条件，以提高电池性能。同时，所获得的热力学模型将是关键贡献者的ICME开发与新型尖晶石阴极材料的LIB。此外，热化学信息对于电池安全和防止危险现象（例如热失控和火焰产生）是必不可少的。

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.