Si Oxidation and H₂ Gassing During Aqueous Slurry Preparation for Li-Ion Battery Anodes

Si has the possibility to greatly increase the energy density of Li-ion battery anodes, though it is not without its problems. One issue often overlooked is the decomposition of Si during large scale slurry formulation and battery fabrication. Here, we investigate the mechanism of H₂ production to understand the role of different slurry components and their impact on the Si oxidation and surface chemistry. Mass spectrometry and in situ pressure monitoring identifies that carbon black plays a major role in promoting the oxidation of Si and generation of H₂. Si oxidation also occurs through atmospheric O₂ consumption. Both pathways, along with solvent choice, impact the surface silanol chemistry, as analyzed by ¹H–²⁹Si cross-polarization magic angle spinning nuclear magnetic resonance (MAS NMR) and attenuated total reflectance Fourier transform infrared spectroscopy (ATR FTIR). An understanding of the oxidation of Si, during slurry processing, provides a pathway toward improving the manufacturing of Si based anodes by maximizing its capacity and minimizing safety hazards

Correction to “Si Oxidation and H₂ Gassing during Aqueous Slurry Preparation for Li-Ion Battery Anodes”

Correction to “Si Oxidation and H₂ Gassing during Aqueous Slurry Preparation for Li-Ion Battery Anodes

Chemical Evolution in Silicon–Graphite Composite Anodes Investigated by Vibrational Spectroscopy

Silicon–graphite composites are under development for the next generation of high-capacity lithium-ion anodes, and vibrational spectroscopy is a powerful tool to identify the different mechanisms that contribute to performance loss. With alloy anodes, the underlying causes of cell failure are significantly different in half-cells with lithium metal counter electrodes compared to full cells with standard cathodes. However, most studies which take advantage of vibrational spectroscopy have only examined half-cells. In this work, a combination of FTIR and Raman spectroscopy describes several factors that lead to degradation in full pouch cells with LiNi_0.5Mn_0.3Co_0.2O₂ (NMC532) cathodes. The spectroscopic signatures evolve after longer term cycling compared to the initial formation cycles. Several side-reactions that consume lithium ions have clear FTIR signatures, and comparison to a library of reference compounds facilitates identification. Raman microspectroscopy combined with mapping shows that the composite anodes are not homogeneous but segregate into graphite-rich and silicon-rich phases. Lithiation does not proceed uniformly either. A basis analysis of Raman maps identifies electrochemically inactive regions of the anodes. The spectroscopic results presented here emphasize the importance of improving electrode processing and SEI stability to enable practical composite anodes with high silicon loadings

Unraveling the Voltage-Fade Mechanism in High-Energy-Density Lithium-Ion Batteries: Origin of the Tetrahedral Cations for Spinel Conversion

High-voltage layered lithium- and manganese-rich (LMR) oxides have the potential to dramatically enhance the energy density of current Li-ion energy storage systems. However, these materials are currently not used commonly; one reason is their inability to maintain a consistent voltage profile (voltage fade) during electrochemical cycling. This report rationalizes the cause of this voltage fade by providing evidence of layered to spinel (LS) structural evolution pathways in the host Li_1.2Mn_0.55Ni_0.15Co_0.1O₂ oxide. By employing neutron powder diffraction, we show that LS structural rearrangement in the LMR oxide occurs through a tetrahedral cation intermediate via the following: (i) diffusion of lithium atoms from octahedral to tetrahedral sites of the lithium layer [(Li_Lioct → Li_Litet] which is followed by the dispersal of the lithium ions from the adjacent octahedral site of the metal layer to the tetrahedral sites of lithium layer [Li_TMoct → Li_Litet]; (ii) migration of Mn from the octahedral sites of the transition-metal layer to the “permanent” octahedral site of lithium layer via tetrahedral site of lithium layer [Mn_TMoct → Mn_Litet → Mn_Lioct)]. These findings open the door to potential routes to mitigate this “atomic restructuring” in the high-voltage LMR composite oxide by manipulating their composition/structure for practical use in high-energy-density lithium-ion batteries

Neutron Diffraction and Magnetic Susceptibility Studies on a High-Voltage Li_1.2Mn_0.55Ni_0.15Co_0.10O₂ Lithium Ion Battery Cathode: Insight into the Crystal Structure

Lithium- and manganese-rich oxides undergo structural transformation and/or atomic rearrangements during the delithiation/lithiation process and ultimately suffer from several issues such as first cycle irreversible capacity and voltage fade. In order to understand the mechanism of these issues, perception of a detailed crystal structure of pristine material is obviously demanding. In this study, combined powder neutron diffraction (ND) and temperature-dependent magnetic susceptibility techniques were employed to investigate the structure of a pristine lithium- and manganese-rich Li_1.2Mn_0.55Ni_0.15Co_0.10O₂ cathode oxide. Rietveld refinement on the experimental ND pattern yields good fits by considering either Li₂MO₃ (M = Co, Mn, Ni) type monoclinic (<i>C2/m</i> space group) phase with 1% of Ni residing in the 4h lithium site or a composite structure consisting of 50% of Li₂MnO₃ type monoclinic (<i>C2/m</i> space group) and 50% LiMO₂ (M = Co, Mn, Ni) type trigonal (<i>R</i>3̅<i>m</i> space group) structure. In the composite structure, 3% Li/Ni site exchange in the trigonal phase is also proposed. Further, temperature-dependent dc magnetic susceptibility shows Curie–Weiss paramagnetic behavior at <i>T</i> ≥ 100 K, and no ordering/deviation of the field cooling (FC) curve in the temperature range 2–320 K indicates the random distribution of metal ions in the transition metal (TM) layer in the trigonal phase. Bifurcation of the zero-field cooling (ZFC) curve from the FC curve showing a magnetic ordering at <i>T</i>_N<i> ∼</i> 50 K reveals the presence of cation ordering in the TM layers arising from a distinct Li₂MnO₃-like phase. These results suggest that the lithium- and manganese-rich oxide with a composition Li_1.2Mn_0.55Ni_0.15Co_0.10O₂ is more likely a composite of monoclinic and trigonal phases. The report also highlights the unique materials diagnostic capability of combined ND and magnetic susceptibility techniques to obtain detailed structural information of complex oxide systems

Effect of Binder Architecture on the Performance of Silicon/Graphite Composite Anodes for Lithium Ion Batteries

Although significant progress has been made in improving cycling performance of silicon-based electrodes, few studies have been performed on the architecture effect on polymer binder performance for lithium-ion batteries. A systematic study on the relationship between polymer architectures and binder performance is especially useful in designing synthetic polymer binders. Herein, a graft block copolymer with readily tunable architecture parameters is synthesized and tested as the polymer binder for the high-mass loading silicon (15 wt %)/graphite (73 wt %) composite electrode (active materials >2.5 mg/cm²). With the same chemical composition and functional group ratio, the graft block copolymer reveals improved cycling performance in both capacity retention (495 mAh/g vs 356 mAh/g at 100th cycle) and Coulombic efficiency (90.3% vs 88.1% at first cycle) than the physical mixing of glycol chitosan (GC) and lithium polyacrylate (LiPAA). Galvanostatic results also demonstrate the significant impacts of different architecture parameters of graft copolymers, including grafting density and side chain length, on their ultimate binder performance. By simply changing the side chain length of GC-<i>g</i>-LiPAA, the retaining delithiation capacity after 100 cycles varies from 347 mAh/g to 495 mAh/g