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.

Increasing the Ni content of a Ni-rich layered positive electrode material is one common way to improve energy density of Li-ion cells but normally leads to shorter cell lifetimes. Single crystalline materials have been shown to improve the cell lifetime by reducing the degree of material degradation. This first study in a two part series investigates the synthesis of Co-free single crystalline LiNi0.95Al0.05O2 and LiNi0.975Mg0.025O2 via a two-step lithiation method. This method consists of a first step heating of the precursors at high temperatures but with deficient Li to grow crystalline particles and then a second step at lower temperature to fully lithiate the material. The synthesized materials were characterized by scanning electron microscopy and X-ray diffraction to understand the impact of synthesis conditions. Single crystal materials were successfully synthesized, and Mg-containing single crystal materials achieved micron-sized particles with as low as 2% Ni in the Li layer. Al-containing single crystal materials could not avoid the formation of Li5AlO4 impurity for all conditions tested. The presence of Li or Mg and high temperatures were identified as factors that promote crystallite growth. Selected samples were characterized electrochemically and compared to their polycrystalline counterparts. Mg-containing single crystal materials are not yet competitive with their polycrystalline counterparts yet, and further understanding and development is needed.

This second study in a two part series investigates the synthesis of Co-free single crystalline Mg-doped LNO via the one-step lithiation method. The synthesized materials were characterized by scanning electron microscopy, X-ray diffraction and particle size analysis to understand the impact of synthesis conditions. Higher heating temperatures promoted grain growth but also increased the Ni content in the Li layer. Increasing the Li/TM ratio does not seem to have an effect on grain growth at lower temperatures but influences the formation of Li2O impurity. The separation of particle aggregates is required to improve the cycling performance of the material. The utilization of a lower temperature step after the calcination step can reduce the Ni content in the Li layer below what would be expected at the calcination temperature, and this can be used to grow larger grains while keeping an acceptable amount of Ni in the Li layer. However, all single crystalline materials are still not yet electrochemically competitive with polycrystalline materials and have lower capacities, higher irreversible capacities and similar cycling fade. The lower capacities of single crystalline materials stem from increased kinetic hindrances to Li diffusion. Cycling single crystalline materials at 55 °C can recover ∼20 mAh g−1 of discharge capacity and yield similar irreversible capacity compared with polycrystalline cells cycled at 30 °C.

Three fluorine-doped lithium nickel oxide samples series (LiNiO2−xFx, LiNi1−xMgxO2−xFx; Li1+x/2Ni1−x/2O2−xFx) were prepared and investigated. It is suggested that fluorine was introduced into the lattice structure during the calcination. As fluorine is introduced into LiNiO2−xFx and LiNi1−xMgxO2−xFx the percentage of Ni (or Ni and Mg) in the Li layer increases for x > 0.05. However, adding excess Li in Li1+x/2Ni1−x/2O2−xFx sucessfully balances the charge differential introduced by fluorine doping therefore very little Ni2+ was created and the lithium layers remain “uncontaminated” by other metals. Data from Li/LiNiO2−xFx, Li/LiNi1−xMgxO2−xFx and Li/Li1+x/2Ni1−x/2O2−xFx cells mirror the percent of cation mixing as determined by X-ray diffraction (XRD) and Rietveld refinement in each case. In situ XRD of Li1.1−xNi0.9O1.8F0.2 shows no multipule phase transitions which further suggests fluorine was successfully doped into the lattice. Acclelerating rate calorimetry (ARC) experiments show a potential safety advantage brought by fluorine doping. pH titration was used to explore if residual LiF (if any) at the surface converted to other lithium compounds (LiOH, Li2O or Li2CO3). No evidence of residual LiF was found.

No abstract