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.

In the pursuit of surpassing the energy density of conventional lithium ion cells, significant efforts have been made to develop lithium metal cells. However, many reports in the literature utilize Li-metal cells with significant excess lithium, resulting in a dramatically reduced practical energy density. In contrast, anode-free cells do not utilize excess lithium; instead, a lithium metal anode is formed in-situ from the stored lithium within the positive electrode during the first charge. Here, we evaluate anode-free lithium metal pouch cells (NMC532||Cu) with operando pressure measurements constrained to different stack pressures between 75-2205 kPa with two different electrolytes, 1M LiPF 6 FEC:DEC (1:2) and 1M LiPF 6 FEC:TFEC (1:2). Increasing the initial average pressure from 75-2200 kPa was found to generally improve cycle life, with the most significant benefits achieved up to 1200 kPa. Cells containing FEC:TFEC electrolyte exhibited a superior initial performance compared to FEC:DEC cells, as evidenced by cycling data and SEM analysis of the lithium morphology. Although generally beneficial, we found that the effect of increased pressure on the performance of cells with different solvent systems was not equal, indicating that the physical properties of electrolyte play an important roll in cells constrained to higher pressures between 1200-2200 kPa.

Monitoring the dynamic chemical and thermal state of a cell during operation is crucial to making meaningful advancements in battery technology as safety and reliability cannot be compromised. Here we demonstrate the feasibility of incorporating optical fiber Bragg grating sensors inside commercial 18650 cells. By adjusting fiber morphologies, wavelength changes associated with both temperature and pressure are decoupled with high accuracy, and this allows for tracking of chemical events such as solid electrolyte interphase formation and structural evolution. Additionally, we demonstrate how multiple sensors can function as a microcalorimeter to monitor the heat generated by the cell. Resolving this heat in detail is not possible with conventional isothermal calorimetry and the importance of assessing the cell's heat capacity contribution is presented. Collectively, these findings offer a scalable solution for screening electrolyte additives, rapidly identifying the best formation processes of commercial batteries, and designing thermal battery management systems with enhanced safety.

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 ...

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