We present a wide range of testing results on an excellent moderate-energy-density lithium-ion pouch cell chemistry to serve as benchmarks for academics and companies developing advanced lithium-ion and other "beyond lithium-ion" cell chemistries to (hopefully) exceed. These results are far superior to those that have been used by researchers modelling cell failure mechanisms and as such, these results are more representative of modern Li-ion cells and should be adopted by modellers. Up to three years of testing has been completed for some of the tests. Tests include long-term charge-discharge cycling at 20, 40 and 55°C, long-term storage at 20, 40 and 55°C, and high precision coulometry at 40°C. Several different electrolytes are considered in this LiNi 0.5 Mn 0.3 Co 0.2 O 2 /graphite chemistry, including those that can promote fast charging. The reasons for cell performance degradation and impedance growth are examined using several methods. We conclude that cells of this type should be able to power an electric vehicle for over 1.6 million kilometers (1 million miles) and last at least two decades in grid energy storage. The authors acknowledge that other cell format-dependent loss, if any, (e.g. cylindrical vs. pouch) may not be captured in these experiments.

Single crystal LiNi 0.5 Mn 0.3 Co 0.2 O 2 (NMC532) was shown to have superior stability at high voltages and elevated temperatures compared to conventional polycrystalline NMC532 by the authors. Conventional LiNi 0.6 Mn 0.2 Co 0.2 O 2 (NMC622) usually offers more capacity than NMC532 when charged to the same upper cutoff voltage so NMC622 is attractive. It is expected that single crystal NMC622 could also provide better performance than typical polycrystalline NMC622 materials. This work explores the synthesis of single crystal LiNi 0.6 Mn 0.2 Co 0.2 O 2 and preferred synthesis conditions were found. A washing and reheating method was used to remove residual lithium carbonate after sintering. The synthesized single crystal NMC622 material worked poorly after the washing-heating treatment without the use of electrolyte additives in the electrolyte. However, with selected additives, single crystal cells outperformed the polycrystalline reference cells in cycling tests. It is our opinion that single crystal NMC622 has a bright future in the Li-ion battery field. showed that single crystal NMC111 could be synthesized using a molten salt method, and a similar method was also applied by Y. Kim et al. 6 to synthesize single crystal NMC811. J. Li et al. 7 introduced a method to synthesize single crystal NMC532 and explored the impact of key synthesis parameters. It was found that the lithium/transition metal molar ratio and sintering temperature played important roles in the synthesis. Excess lithium can provide a flux-type environment which facilitates particle growth.8 High sintering temperature also assists the particle growth significantly. NMC622 has higher specific capacity and better rate capability compared to NMC532 at the same voltage, 1 which makes it very attractive. In this work, the synthesis of single crystal NMC622 is explored with the goal of attaining optimized electrochemical performance. For conventional polycrystalline NMC material synthesis, different NMC ratios require different synthesis conditions. 1 There are no publications about single crystal NMC622 synthesis that have been reported in the scientific literature. Although Wang et al. 9 reported the synthesis of single crystal NMC622, their synthesized materials were made up of agglomerates with individual grain size less than 1 μm. In our view, single crystal materials should be individual grains of greater than 2 μm. The electrochemical properties of single crystal NMC622 (SC622) were compared with polycrystalline NMC622 (PC622) made with conventional methods. The impact of some electrolyte additives on the charge-discharge cycling performance of the materials synthesized was also investigated. This work will be of interest to both industrial and academic researchers developing single crystal NMC materials for long lifetime lithium ion batteries. O, 98%, Alfa Aesar), sodium hydroxide (NaOH, 98%, Alfa Aesar), ammonium hydroxide (NH 4 OH, 28.0-30.0%, Sigma-Aldrich). All aqueous solutions used in the precursor synthesis were prepared with deion...

Adding esters as co-solvents to Li-ion battery electrolytes can improve low-temperature performance and rate capability of cells. This work uses viscosity and electrolytic conductivity measurements to evaluate electrolytes containing various ester co-solvents, and their suitability for use in high-rate applications is probed. Among the esters studied, methyl acetate (MA) outperforms other esters in its impact on the conductivity and viscosity of the electrolyte. Therefore, viscosity and conductivity were measured as a function of temperature and LiPF 6 concentration for electrolytes ethylene carbonate (EC): linear carbonate: MA in the ratio 30:(70-x):x, where linear carbonate = {ethyl methyl carbonate (EMC), dimethyl carbonate (DMC)}, and x = {0, 10, 20, 30}. Adding MA leads to an increase in conductivity and decrease in viscosity over all conditions. Calculations of electrolyte properties from a model based on a statistical-mechanical framework, the Advanced Electrolyte Model (AEM), are compared to all measurements and excellent agreement is found. All electrolytes studied roughly agree with a Stokes' Law model of conductivity. A Walden analysis shows that the ionicity of the electrolyte is not significantly impacted by either MA content or LiPF 6 concentration. Li [Ni 0.5 Typical performance metrics of Li-ion batteries such as lifetime and power capabilities depend strongly on the electrolyte used. The ionic conductivity of the electrolyte is one transport property that helps to determine how fast a cell can be charged or discharged, and has been reported for a vast number of aqueous and non-aqueous electrolyte systems.1-14 While it does not give a full picture of ionic transport in an electrolyte, conductivity can be measured easily and accurately, giving a rapid evaluation of the electrolyte in question. In addition to conductivity, the dielectric constants and viscosities of the constituent solvents must be considered.5,15 For a more rigorous analysis of cell performance using physics-based models, other transport properties such as Li-ion transference number, diffusivity, and activity coefficient are required. 9,[16][17][18][19] Traditional solvent blends for Li electrolytes have been made with mixtures of ethylene carbonate (EC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC) and dimethyl carbonate (DMC). EC has a high dielectric constant, aiding the disassociation of the lithium salt in solution. Traditionally, EC has also been required in the electrolyte to help form a passivating solid electrolyte interphase (SEI) on a graphite negative electrode. 20 DEC, EMC and DMC have lower viscosities and melting points than EC, and when mixed with EC result in an electrolyte with a good balance between desirable electrochemical properties, high dielectric constant, and low viscosity. [21][22][23][24] Aliphatic esters have lower melting points and viscosities than "low viscosity" linear carbonates such as EMC or DMC. 21,25,26 Many studies have investigated the impact of esters on the performance of Liion ...

Eventual rapid capacity loss or "rollover" failure of lithium-ion cells during long-term cycling (>3000 cycles in many cases) at room temperature was studied with Li[Ni 0.5 Mn 0.3 Co 0.2 ]O 2 /graphite pouch cells. The effects of positive electrode material coating, electrolyte additives, upper cutoff voltage, LiPF 6 concentration, cell rest periods, electrode thickness, graphite type and electrolyte solvent formulation were probed. Cells were tested under 1C charge and discharge with "rate maps" (discharges at C/20, C/2, 1C, 2C, 3C) applied every 100 cycles. The loss of high rate capability (3C) is shown to be an early warning of impending rollover failure. Electrochemical impedance spectroscopy (EIS) and studies of symmetric cells made using electrodes from disassembled cells demonstrate that impedance growth at the positive electrode and associated DC resistance growth is responsible for rollover failure in these cells. Ultra-high precision coulometry (UHPC) shows that cells that were charged to higher voltages, which increase the rate of electrolyte oxidation, or show higher rates of electrolyte oxidation at the same cutoff potential due to changes in electrolyte formulation, normally are more prone to eventual rollover failure. In order to avoid rollover and extend the cycling life of Li-ion cells, it is important to choose optimal cell chemistries, some of which are enumerated in this report.

Ferroelectric materials can be utilized for fabricating photodetectors because of the photovoltaic effect. Enhancing the photovoltaic performance of ferroelectric materials is still a challenge. Here, a self-powered ultraviolet (UV) photodetector is designed based on the ferroelectric BiFeO (BFO) material, exhibiting a high current/voltage response to 365 nm light in heating/cooling states. The photovoltaic performance of the BFO-based device can be well modulated by applying different temperature variations, where the output current and voltage can be enhanced by 60 and 75% in heating and cooling states, respectively. The enhancement mechanism of the photocurrent is associated with both temperature effect and thermo-phototronic effect in the photovoltaic process. Moreover, a 4 × 4 matrix photodetector array has been designed for detecting the 365 nm light distribution in the cooling state by utilizing photovoltage signals. This study clarifies the role of the temperature effect and the thermo-phototronic effect in the photovoltaic process of the BFO material and provides a feasible route for pushing forward practical applications of self-powered UV photodetectors.

The effect of LiPO 2 F 2 as an electrolyte additive in Li[Ni 0.5 Mn 0.3 Co 0.2 ]O 2 (NMC532)/graphite pouch cells was examined using ultra high precision coulometry (UHPC), electrochemical impedance spectroscopy (EIS), storage testing, gas evolution measurements, isothermal calorimetry and long term charge-discharge cycling. Comparisons to the well-known additive, vinylene carbonate (VC) were made. LiPO 2 F 2 is an effective additive for NMC532/graphite pouch cells since it was found to improve coulombic efficiency, decrease parasitic heat flow, improve charge-discharge cycle lifetime and decrease impedance growth. The composition of the solid electrolyte interphases (SEI) on both electrodes was examined by X-ray photoelectron spectroscopy in cases where LiPO 2 F 2 was used or not used. The effect of combining methyl acetate, as a co-solvent to improve rate capability, and LiPO 2 F 2 was also investigated using long term cycling testing at 20 • C. Overall, LiPO 2 F 2 is shown to be an extremely valuable electrolyte additive, more effective than VC in these cells.

3D flower-like β-Ni(OH)2/GO/CNTs composite prepared via facile phase transformation method exhibited high specific capacitance (96% of theoretical pseudocapacitance at 2 A g−1) and good cycling performance.

Fast-charging lithium-ion cells require electrolyte solutions that balance high ionic conductivity and chemical stability. The introduction of an organic ester co-solvent is one route that can improve the rate capability of a cell. Several new co-solvent candidates were identified based on viscosity, permittivity (dielectric constant), and DFT-calculated electrochemical stability windows. Several formate, nitrile, ketone, and amide co-solvents are shown to increase the ionic conductivity of lithium hexafluorophosphate in conventional organic-carbonate-based solutions. Based on gas production during the first formation cycle in Li[Ni 1-x-y Co x Al y ]O 2 /graphite-SiO pouch cells, five candidates were identified: methyl formate (MF), ethyl formate (EF), propionitrile (PN), isobutyronitrile (iBN), and dimethyl formamide (DMF). High temperature storage (60 • C), long-term cycling, and ultrahigh-precision coulometry results indicate that MF offers the greatest balance between conductivity increase and cell lifetime. Future work is encouraged to develop more stable solution chemistries that incorporate MF. PN may prove useful for low temperature (< 40 • C) applications.