Dominique Guyomard

Vehicle electrification currently relies on lithium-ion batteries using nickel, manganese and cobalt (NMC)-based lamellar oxides as positive electrode materials. In order to achieve higher energy densities, the market is now moving towards NMC with high nickel content. Nevertheless, these materials have been widely demonstrated to suffer from serious off-gassing problems that reduce cycle life and pose safety concerns. Not only gases resulting from the formation of SEI at the negative electrode, but the production of O2, CO and CO2 have also been noted by different research groups.^1–3 Despite the large number of studies analyzing the material during and after cycling, we noted a lack of in-depth characterization of the surface of Nickel-rich NMCs in their initial state. The need for such information is increasingly necessary with the recent development of new technologies for surface modification such as coating to limit the instability of high Nickel content NMCs.^4,5 The surface reactivity of Ni-rich layered transition metal oxides is instrumental to the performance of batteries based on these positive electrode materials. Most often, strong surface modifications are detailed with respect to a supposed ideal initial state. The study the LiNi0.8Mn0.1Co0.1O2 (NMC811) cathode material in its pristine state, hence before any contact with electrolyte or cycling, was performed thanks to advanced microscopy and spectroscopy techniques in order to fully characterize its surface down to the nanometer scale. Scanning transmission-electron microscopy-electron energy-loss spectroscopy (STEM-EELS), solid state nuclear-magnetic-resonance (SS-NMR) and X-rays photoelectron spectroscopy (XPS) are combined and correlated in an innovative manner. Specifically, using a high magnetic field NMR spectrometer, it was possible to evaluate the total amount of diamagnetic Li in the samples. Thanks to XPS it was then possible to identify the lithiated species present on the surface and to use such information to better deconvolve the NMR spectra. Li2O, Li2SO4 and LiOH were identified as the main contaminants on the surface of NMC in its initial state. On the other hand, the quantity of Li2CO3 initially estimated by XPS could be substantially re-evaluated using NMR (54% by XPS vs. only 1% by NMR). These two techniques, providing only partial and often imprecise information when used separately, have proven to be fundamental instruments in the analysis of surface species when used in a complementary manner. The results demonstrate that in usual storage conditions after synthesis, the extreme surface is already chemically different from nominal values. In particular, nickel is found in a reduced state compared to the bulk value and a Mn enrichment is determined in the first few nanometers of primary particles. Further exposition to humid air allows for quantifying the formed lithiated species per gram of active material, identifying their repartition and proposing a reaction path in relation with the instability of the surface. Modifying synthesis conditions impacts noticeably the previously identified surface particularities and, consequently, the materials reactivity. References : (1) Jung, R.; Metzger, M.; Maglia, F.; Stinner, C.; Gasteiger, H. A. Oxygen Release and Its Effect on the Cycling Stability of LiNi_xMn_yCo_zO₂ (NMC) Cathode Materials for Li-Ion Batteries. Journal of The Electrochemical Society 2017, 164 (7), A1361–A1377. https://doi.org/10.1149/2.0021707jes. (2) Renfrew, S. E.; McCloskey, B. D. Residual Lithium Carbonate Predominantly Accounts for First Cycle CO2 and CO Outgassing of Li-Stoichiometric and Li-Rich Layered Transition-Metal Oxides. J. Am. Chem. Soc. 2017, 139 (49), 17853–17860. https://doi.org/10.1021/jacs.7b08461. (3) Renfrew, S. E.; McCloskey, B. D. The Role of Electrolyte in the First-Cycle Transformations of LiNi _0.6 Mn _0.2 Co _0.2 O ₂. J. Electrochem. Soc. 2019, 166 (13), A2762–A2768. https://doi.org/10.1149/2.1561912jes. (4) Zhang, H.; Liu, H.; Piper, L. F. J.; Whittingham, M. S.; Zhou, G. Oxygen Loss in Layered Oxide Cathodes for Li-Ion Batteries: Mechanisms, Effects, and Mitigation. Chem. Rev. 2022, acs.chemrev.1c00327. https://doi.org/10.1021/acs.chemrev.1c00327. (5) Manthiram, A.; Song, B.; Li, W. A Perspective on Nickel-Rich Layered Oxide Cathodes for Lithium-Ion Batteries. Energy Storage Materials 2017, 6, 125–139. https://doi.org/10.1016/j.ensm.2016.10.007. Figure 1

Lithium metal batteries are inspiring renewed interest in the battery community because the most advanced designs of Li-ion batteries could be on the verge of reaching their theoretical specific energy density values. Among the investigated alternative technologies for electrochemical storage, the all-solid-state Li battery concept based on the implementation of dry solid polymer electrolytes appears as a mature technology not only to power full electric vehicles but also to provide solutions for stationary storage applications. With an effective marketing started in 2011, BlueSolutions keeps developing further the so-called lithium metal polymer batteries based on this technology. The present study reports the electrochemical performance of such Li metal batteries involving indigo carmine, a cheap and renewable electroactive non-soluble organic salt, at the positive electrode. Our results demonstrate that this active material was able to reversibly insert two Li at an average potential of ≈2.4 V vs. Li⁺/Li with however, a relatively poor stability upon cycling. Post-mortem analyses revealed the poisoning of the Li electrode by Na upon ion exchange reaction between the Na countercations of indigo carmine and the conducting salt. The use of thinner positive electrodes led to much better capacity retention while enabling the identification of two successive one-electron plateaus.

The urgent demand of the EV industry for high energy density cathode materials is currently leading the battery market towards Ni-rich NMCs. Despite that, the gassing phenomenon that affects these materials has huge impacts on their electrochemical properties and causes security issues that prevent the commercialization of 80% Ni-rich NMC. In order to obtain a fundamental understanding of this gassing generation, we decided to focus on the surface reactivity of the pristine NMC811 provided by Umicore, with emphasis on the material surface’s and bulk’s changes during the native contamination layer formation. A multi-analytical approach is thus required to analyse all the aspects of such a complex system. The sapient use of high field ⁷Li MAS-NMR allowed us to successfully filter the signal of the diamagnetic compounds at the surface of the material and to quantify the corresponding environments. The speciation of these compounds, not being possible by MAS-NMR, was defined by low temperature XPS experiments. It was thence possible to characterise the reactive surface of the primary particles in contact with this contamination layer at the nanometric scale by STEM-EELS with both high energy and high spatial resolutions. The oxidation state and the crystalline phase were successfully determined crossing the high quality experimental spectra recorder with the K2 counting direct detector (Gatan) installed on our new Themis Z G3 (Thermo Fisher Scientific) and EELS edges simulations. On the other hand, low field ¹H MAS-NMR gave us a new insight on the proton environments enabling us to clearly see the presence of a proton chemically bonded inside the material for the first time and to correlate it with the surface reactivity investigated with the other techniques. The combined use of these advanced characterisation techniques, all available in the IMN, allowed us to shed a new light on the understanding of the pristine industrial NMC811 with always the same material history.

In order to obtain higher energy densities for electromobility applications, the market is now heading towards high-nickel content NMCs. However, these materials suffer from severe gassing issues decreasing the cycle life and causing safety problems. While it is agreed that the O₂ evolution is coming from oxygen lattice oxidation at the end of charge, the source of CO and CO₂ gassing is still under debate. In this context, we report here a systematic study of NMC811 pristine material surface contaminations obtained after storage in different controlled environments. We use a multi-analytical approach involving combined MAS-NMR, XPS and STEM-EELS to provide a full material characterisation before cycling. The chemical environment of the Li present in the paramagnetic bulk of the material is successfully determined by means of ⁷Li MAS-NMR at low field (200 MHz). High field ⁷Li MAS-NMR (500 MHz) allows the quantification of the surface diamagnetic Li. Low field ¹H MAS-NMR gives insights on the proton bulk and surface environments. STEM-EELS mapping is performed with both high energy and high spatial resolution using our new TEM/STEM Themis Z G3 (Thermo Fisher Scientific) equipped with a double camera GIF spectrometer. We obtain a good multi-elemental chemistry mapping quantification as well as the accurate analysis of the fine structure of the L3/L2 Ni edges thanks to the use of an excited monochromator. Putting together all characterisation results, we achieved a thorough analysis of primary particles surface contamination after different controlled storage conditions, that will be correlated with gassing measurements and cell cycling stability.

Lithium‐ion batteries (LIBs) have become ubiquitous power sources for small electronic devices, electric vehicles, and stationary energy storage systems. Despite the success of LIBs which is acknowledged by their increasing commodity market, the historical evolution of the chemistry behind the LIB technologies is laden with obstacles and yet to be unambiguously documented. This Viewpoint outlines chronologically the most essential findings related to today's LIBs, including commercial electrode and electrolyte materials, but furthermore also depicts how the today popular and widely emerging solid‐state batteries were instrumental at very early stages in the development of LIBs.

An industry‐relevant method for pre‐lithiation of lithium‐ion capacitors to balance the first charge irreversibility is demonstrated, which addresses the prime bottleneck for their market integration. Based on a composite positive electrode that integrates pyrene monomers and an insoluble lithiated base, Li₃PO₄, a “cascade‐type” process involving two consecutive irreversible reactions is proposed: i) oxidative electropolymerization of the pyrene moieties releases electrons and protons; ii) protons are captured by Li₃PO₄ and exchanged for a stoichiometric amount of Li⁺ into the electrolyte. (¹H, ¹⁹F, and ³¹P) NMR spectroscopy, operando X‐ray diffraction, and Raman spectroscopy support this mechanism. By decoupling the irreversible source of lithium ions from electrons, the cascade‐type pre‐lithiation allows the simultaneous enhancement of the capacity of the positive electrode, thanks to p‐doping of the resulting polymer. Remarkably, the proton scavenging properties of Li₃PO₄ also boost the polymerization process, which enables a 16% increase in capacity without detrimental effect on power properties and cyclability. Full cells integrating a cheap carbon black based negative electrode, show much‐improved capacity of 17 mAh g^‐1_electrodes (44 F g^‐1_electrodes, 3–4.4 V) and excellent stability over 2200 cycles at 1 A g^‐1. Thanks to its versatile chemistry and flexibility this approach in principle can be applied to any kind of ion‐battery.

Aqueous batteries, particularly those integrating organic active materials functioning in a neutral pH environment, stand out as highly promising contenders in the stationary electrochemical storage domain, owing to their unparalleled safety, sustainability, and low‐cost materials. Herein, a novel di‐block oligomer, serving as the negative electrode of an all‐organic aqueous battery, is shown to offer exceptional output capabilities. The battery's performance is further enhanced by a unique intermixed p/n‐type storage mechanism, which is able to simultaneously exchange light and naturally abundant Na⁺, Mg²⁺, and Cl⁻. Reaching up to 105 mAh g⁻¹, this system shows remarkable capacity retention for several thousand cycles (6500 cycles, ≈40 days) in various neutral electrolytes, including raw ocean water (≈3000 cycles, ≈75 days). The surprisingly fast kinetics of this di‐block oligomer allow to attain an unmatched specific capacity of near to 60 mAh g⁻¹_electrode while entirely devoid of conducting additives, and more than 80 mAh g⁻¹_electrode with 10% carbon additive, as well as displaying an areal capacity as high as 3.4 mAh cm⁻² at C rate. Full cell validation was demonstrated over 1600 cycles by virtue of a commercial 2,2,6,6‐tétraméthylpipéridin‐1‐yl)oxyl (TEMPO) molecule, which permitted an energy density of close to 40 Wh kg⁻¹_materials at C rate in a self‐pH‐buffered and inexpensive aqueous electrolyte.