Recent developments in cathode materials for lithium ion batteries

Future generations of electric vehicles require driving ranges of at least 300 miles to successfully penetrate the mass consumer market. A significant improvement in the energy density of lithium batteries is mandatory while also maintaining similar or improved rate capability, lifetime, cost, and safety. The vast majority of electric vehicles that will appear on the market in the next 10 years will employ nickel-rich cathode materials, LiNi1–x–yCoxAlyO2 and LiNi1–x–yCoxMnyO2 (x + y < 0.2), in particular. Here, the potential and limitations of these cathode materials are critically compared with reference to realistic target values from the automotive industry. Moreover, we show how future automotive targets can be achieved through fine control of the structural and microstructural properties.

Nickel-Rich Layered Cathode Materials for Automotive Lithium-Ion Batteries: Achievements and Perspectives

Ni-rich layered oxides and Li-rich layered oxides are topics of much research interest as cathodes for Li-ion batteries due to their low cost and higher discharge capacities compared to those of LiCoO2 and LiMn2O4. However, Ni-rich layered oxides have several pitfalls, including difficulty in synthesizing a well-ordered material with all Ni3+ ions, poor cyclability, moisture sensitivity, a thermal runaway reaction, and formation of a harmful surface layer caused by side reactions with the electrolyte. Recent efforts towards Ni-rich layered oxides have centered on optimizing the composition and processing conditions to obtain controlled bulk and surface compositions to overcome the capacity fade. Li-rich layered oxides also have negative aspects, including oxygen loss from the lattice during first charge, a large first cycle irreversible capacity loss, poor rate capability, side reactions with the electrolyte, low tap density, and voltage decay during extended cycling. Recent work on Li-rich layered oxides has focused on understanding the surface and bulk structures and eliminating the undesirable properties. Followed by a brief introduction, an account of recent developments on the understanding and performance gains of Ni-rich and Li-rich layered oxide cathodes is provided, along with future research directions.

Nickel-Rich and Lithium-Rich Layered Oxide Cathodes: Progress and Perspectives

Ni-rich Li[NixCoyMn1–x–y]O2 cathodes (x = 06, 08, 09, and 095) were tested to characterize the capacity fading mechanism of extremely rich Ni compositions Increasing the Ni fraction in the cathode delivered a higher discharge capacity (1929 mA h g–1 for Li[Ni06Co02Mn02]O2 versus 2350 mA h g–1 for Li[Ni095Co0025Mn0025]O2); however, the cycling stability was substantially reduced Li[Ni06Co02Mn02]O2 and Li[Ni08Co01Mn01]O2 retained more than 95% of their respective initial capacities after 100 cycles, while the capacity retention of Li[Ni09Co005Mn005]O2 and Li[Ni095Co0025Mn0025]O2 was limited to 85% during the same cycling period The relatively inferior cycling stability of Li[NixCoyMn1–x–y]O2 with x > 08 is attributed to the phase transition near the charge-end, causing an abrupt anisotropic shrinkage (or expansion during discharge), which was suppressed for compositions of x < 08 Residual stress stemming from the phase transition destabilized the internal microcracks and allowe

Capacity Fading of Ni-Rich Li[NixCoyMn1–x–y]O2 (0.6 ≤ x ≤ 0.95) Cathodes for High-Energy-Density Lithium-Ion Batteries: Bulk or Surface Degradation?

High-nickel layered oxide cathode materials will be at the forefront to enable longer driving-range electric vehicles at more affordable costs with lithium-based batteries. A continued push to higher energy content and less usage of costly raw materials, such as cobalt, while preserving acceptable power, lifetime and safety metrics, calls for a suite of strategic compositional, morphological and microstructural designs and efficient material production processes. In this Perspective, we discuss several important design considerations for high-nickel layered oxide cathodes that will be implemented in the automotive market for the coming decade. We outline various intrinsic restraints of maximizing their energy output and compare current/emerging development roadmaps approaching low-/zero-cobalt chemistry. Materials production is another focus, relevant to driving down costs and addressing the practical challenges of high-nickel layered oxides for demanding vehicle applications. We further assess a series of stabilization techniques on their prospects to fulfill the aggressive targets of vehicle electrification. The development of high-nickel layered oxide cathodes represents an opportunity to realize the full potential of lithium-ion batteries for electric vehicles. Manthiram and colleagues review the materials design strategies and discuss the challenges and solutions for low-cobalt, high-energy-density cathodes.

https://www.nature.com/articles/s41560-019-0513-0.pdf?proof=t

High-nickel layered oxide cathodes for lithium-based automotive batteries

We used a suite of transmission electron microscopy (TEM) and associated electron spectroscopy methods to examine the local structure and changes in the electronic structure of LiNi 0.8 Co 0.15 Al 0.05 O 2 positive electrode material. We found a scattered rock-salt phase near grain surfaces and grain boundaries, where Ni 3+ turned to Ni 2+ , deduced from relative intensity ratios and fine structures of the L 2,3 white-line peaks of the transition metals. The spatial distribution of the degraded phase throughout the secondary particle was found using a scanning TEM-electron energy loss spectroscopy spectral imaging technique and multivariate analysis. The degradation process and its relationship to the surface reactions with electrolytes is discussed based on the spatial-distribution map of the degraded phases.

Capacity-Fading Mechanisms of LiNiO2-Based Lithium-Ion Batteries II. Diagnostic Analysis by Electron Microscopy and Spectroscopy

Local atomic and electronic structures around Mg and Al dopants in LiNiO2 electrodes studied by XANES and ELNES and first-principles calculations

The demand for analysis of trace elements in atomically localized areas by electron energy-loss spectroscopy (EELS) in transmission electron microscopy is increasing. Unfortunately, the prolonged data acquisitions required to achieve an acceptable signal-to-noise ratio (SNR) tend to deteriorate the energy resolution because of spectral drifts due to instrumental instability. We developed a macroscript for a Gatan Digital Micrograph(TM) to control an ENFINA 1000 EEL spectrometer that corrects for energy drifts during data accumulation. The script successfully achieved a core-loss spectrum for a sample having approximately 1 at% elemental concentration, and provided a sufficient SNR for chemical state analysis.

Energy-drift correction of electron energy-loss spectra from prolonged data accumulation of low SNR signals

We applied Pixon deconvolution as introduced in Part I to several practical, examples of low signal-to-noise ratio (SNR), electron energy-loss spectra with a goal toward restoring their fine spectral features and/or improving the energy resolution. We demonstrate that by directly fitting the two-dimensional spectral data recorded on the CCD; the method enables us to reveal fine spectral structures. Consequently, Pixon reconstruction extends the ability to probe electronic states in very spatially localized areas, a capability currently unique to our method.

Spectral restoration and energy resolution improvement of electron energy-loss spectra by Pixon reconstruction: II. Application to practical ELNES analysis of low SNR.

Although LiNiO2 based materials are expected for cathodes of Li rechargeable batteries in high-power use, the electrochemical properties of the cathodes are degraded by charge-discharge cycles at elevated temperatures[1]. Small amounts of Al and Mg are doped so as to suppress the degradation. The purpose of this study is a cathode diagnostics by two different approaches. One is the local environment analysis of the dilute dopants by TEM-EELS and first principles calculations. The other is STEMEELS imaging with a multi-variate analysis for spatial distribution of the degraded areas in the cathode active materials.

Yusuke Sasano

Papers

Capacity-Fading Mechanisms of LiNiO2-Based Lithium-Ion Batteries II. Diagnostic Analysis by Electron Microscopy and Spectroscopy

Local atomic and electronic structures around Mg and Al dopants in LiNiO2 electrodes studied by XANES and ELNES and first-principles calculations

Energy-drift correction of electron energy-loss spectra from prolonged data accumulation of low SNR signals

Spectral restoration and energy resolution improvement of electron energy-loss spectra by Pixon reconstruction: II. Application to practical ELNES analysis of low SNR.

Diagnostic of Li battery cathode by EELS, first principles calculation and spectrum-imaging with multi-variate analysis