The nucleation and growth of Li metal during deposition and the associated dendrite penetration are the critical and fundamental issues influencing the safety and power density of solid‐state lithium metal batteries (SSLBs). However, investigations on Li metal deposition/dissolution especially the formation and growth of Li dendrites and their determining factors in the all‐solid‐state electrochemical systems are still lacking. In this work, in situ observations of the Li metal growth process, and defects induced heterogeneous deposition under cathodic load, are reported. By exploiting in situ scanning electron microscopy, along with electrochemical analytical approaches, the spatial distribution and morphological evolution of the deposited Li at the electrode|solid electrolyte interface are obtained and discussed. This investigation reveals that the formation of lithium whiskers is decided by the local Li ion flux and the deposition active sites, which are closely dependent on the content and types of defects in the polycrystalline electrolyte. Moreover, the defect regions exhibit faster Li deposition kinetics and higher nucleation tendency. These results can advance the fundamental understanding of the Li penetration mechanism in SSLBs.

Solid electrolytes hold the promise for enabling high-performance lithium (Li) metal batteries, but suffer from Li-filament penetration issues. The mechanism of this rate-dependent failure, especially the impact of the electrochemo-mechanical attack from Li deposition, remains elusive. Herein, we reveal the Li deposition dynamics and associated failure mechanism of solid electrolyte by visualizing the Li|Li7La3Zr2O12 (LLZO) interface evolution via in situ transmission electron microscopy (TEM). Under a strong mechanical constraint and low charging rate, the Li-deposition-induced stress enables the single-crystal Li to laterally expand on LLZO. However, upon Li “eruption”, the rapidly built-up local stress, reaching at least GPa level, can even crack single-crystal LLZO particles without apparent defects. In comparison, Li vertical growth by weakening the mechanical constraint can boost the local current density up to A·cm−2 level without damaging LLZO. Our results demonstrate that the crack initiation at the Li|LLZO interface depends strongly on not only the local current density but also the way and efficiency of mass/stress release. Finally, potential strategies enabling fast Li transport and stress relaxation at the interface are proposed for promoting the rate capability of solid electrolytes.

Dendrite growth severely hinders the practical use of lithium metal as an ideal battery anode. To realize controlled Li plating, tremendous efforts have been focused on modifying the lithiophilicity chemistry of the anode hosts. Instead, we attempt to address this issue from a geometry perspective. We herein adopt carbon nanobowls (CBs) as a model host to study the geometry-guided Li growth behaviors by in situ electron microscopy. The strong effect of surface curvature is clearly demonstrated: Li metal is always guided to deposit on the concave surface of an isolated CB instead of the convex surface. The fully confined hollow cavity is more favorable for Li deposition in comparison to the partially confined spaces, such as the hemispherical concavity of a CB and interstitial voids between neighboring CBs. Density functional theory calculations elucidate that the geometry-guided Li growth is driven by the energy minimization associated with the formation of low-energy Li/C interfaces.

Despite the high specific capacity of silicon as a promising anode material for the next-generation high-capacity Li-ion batteries (LIBs), its practical applications are impeded by the rapid capacity decay during cycling. To tackle the issue, herein, a bindergrafting strategy is proposed to construct a covalently cross-linked binder [carboxymethyl cellulose/phytic acid (CMC/PA)], which builds a robust branched network with more contact points, allowing stronger bonds with Si nanoparticles by hydrogen bonding. Benefitting from the enhanced mechanical reliability, the resulting Si-CMC/PA electrodes exhibit a high reversible capacity with improved long-term cycling stability. Moreover, an assembled full cell consisting of the as-obtained Si-CMC/PA anode and commercial LiFePO 4 cathode also exhibits excellent cycling performance (120.4 mA h g −1 at 1 C for over 100 cycles with 88.4% capacity retention). In situ transmission electron microscopy was employed to visualize the binding effect of CMC/PA, which, unlike the conventional CMC binder, can effectively prevent the lithiated Si anodes from cracking. Furthermore, the combined ex situ microscopy and X-ray photoelectron spectroscopy analysis unveils the origin of the superior Li-ion storage performance of the Si-CMC/PA electrode, which arises from its excellent structural integrity and the stabilized solid−electrolyte interphase films during cycling. This work presents a facile and efficient binder-engineering strategy for significantly improving the performance of Si anodes for next-generation LIBs.

Cation-disordered rock-salt oxides with the O2–/O2 n– redox reaction, such as Li1.2Mn0.4Ti0.4O2 (LMTO), are critical Li-rich cathode materials for designing high-energy-density batteries. Understanding the cationic–anionic redox accompanying the structural evolution process is really imperative to further improve the performance. In this work, the cationic–anionic redox and capacity degradation mechanism of carbon-coated LMTO during (dis)­charge processes are elucidated by combining in situ X-ray diffraction, X-ray absorption near-edge spectroscopy, differential electrochemical mass spectrometry, transmission electron microscopy, and electrochemical analyses. It is concluded that the redox reaction of Mn2+/Mn4+ is quite stable, while the severe degradation is mainly caused by the O2–/O2 n– redox process. Moreover, we clearly clarify how the cationic–anionic interplay governs sluggish kinetics, large polarization, and capacity fading in LMTO, and reveal for the first time that a certain amount of carbon coating is capable of suppressing the irreversible lattice oxygen loss and results in an encouraging cycling performance. In summary, we elucidate the degradation of cationic–anionic redox processes in cation-disordered cathode materials and propose strategies for adjusting the electronic/ionic conductivity of the electrodes to modulate the oxygen redox reactions, setting a new direction for the design of better cation-disordered oxides.