Aijia Wei

Solid-state lithium metal batteries with poly(ethylene glycol) acrylate (PEGA) solid electrolytes are considered one of the promising candidates for next-generation power sources. Constructing composite solid electrolytes (CSEs) by adding Li_1.3Al_0.3Ti_1.7(PO₄)₃ (LATP) particles into the PEGA matrix is a fantastic way to improve their overall electrochemical properties. However, the inorganic LATP particles tend to agglomerate in the organic PEGA matrix. Designing LATP into a 3D porous oxide electrolyte framework can address the agglomeration issue effectively, but the preparation of the LATP framework is complicated and difficult to reproduce on a large scale. In this work, a scalable CSE with a PEGA matrix and LATP framework is directly prepared on a cathode by integrating with polyvinylidene difluoride (PVDF) and an organic solvent, which is friendly to operate and matches the production of mainstream LIBs. The designed CSE generates a fantastic conductivity of 0.22 mS cm⁻¹ and Li⁺ transference number (t_Li+ = 0.60) at room temperature. A Li/Li symmetric cell fabricated using the designed CSE can cycle steadily for 1645 h at 0.1 mA cm⁻² and room temperature. Li/LiFePO₄ full cells were assembled to assess battery performance, which delivers excellent stable discharge capacity (146.7 mA h g⁻¹ at 0.5C) and cycling stability with a capacity retention of 96.9% at 0.5C after 300 cycles at room temperature. The work addresses the issue of difficult reproduction of a 3D porous oxide electrolyte framework and provides a CSE with a 3D porous LATP framework possessing a high development potential and its feasible scale-up preparation method.

Spinel-type LiNi_0.5Mn_1.5O₄ (LNMO) materials have attracted broad attention as components of rechargeable lithium-ion batteries (LIBs) due to their high energy density. However, continuous decomposition of electrolyte at high working voltage hinders their practical application in carbonate-solvent-based electrolytes. In this work, 4-methyl-1,3,2-dioxathiolane-2,2-dioxide (MDTD) was added as a functional electrolyte additive to the standard electrolyte (i.e., 1 M LiPF₆–ethylene carbonate/ethyl methyl carbonate/dimethyl carbonate) to enhance the electrochemical performances of LNMO-based LIBs. Specifically, the addition of a 0.5% additive to the standard electrolyte significantly improved the capacity retention of LNMO/Li half-cells from 78.5 to 95.8% after 500 cycles at 5C, increased the capacity retention of LNMO/graphite full-cells from 70.8 to 80.9% after 100 cycles at 0.5C, and enhanced the capacity retention of LNMO/LTO full cells from 37.2 to 81.8% after 200 cycles at 5C. In addition, the standard electrolyte containing 0.5% MDTD also improved the cycling performance of LNMO/Li half-cells at 45 °C, expanding the applicable temperature range. Comprehensive characterization combined with theoretical calculations allowed us to reveal the action mechanism of the additive. In this mechanism, MDTD is decomposed and subsequently involved in the decoration of the electrode–electrolyte interfacial films (for the LNMO, Li, and graphite electrodes), endowing it with improved conductivity, protection, and resistance to electrolyte oxidation/reduction decomposition features. These findings suggest that the use of the MDTD additive is a promising strategy to optimize high-voltage electrolytes for the industrialization of LNMO-based LIBs.

A solid-state ball-milling method was used to prepare the Li⁺/F⁻ co-doped LiNi_0.5Mn_1.5O₄ materials. XRD characterizations reveal that the Li⁺/F⁻ co-doping decreases the Li_xNi_1-xO impurities contents and enhances the structural stability. It can be seen from SEM analysis that the crystal morphology of LiNi_0.5Mn_1.5O₄ material changes into a phase octahedron morphology because of Li⁺/F⁻ co-doping. The electrochemical performance tests results show Li_1.03Ni_0.5Mn_1.5O_3.97F_0.03 material possesses a higher rate capability. Specifically, the discharge capacity of Li_1.03Ni_0.5Mn_1.5O_3.97F_0.03 material at 2, 3, 5, and 7 C-rate was 127.3, 120.4, 103.3 and 79.0 mAh·g⁻¹, respectively, while that of the Pure LNMO yields only 117.7, 109.8, 88.3 and 54.2 mAh·g⁻¹.

K⁺/Cl⁻ and K⁺/F⁻ co-doped LiNi_0.5Mn_1.5O₄ (LNMO) materials were successfully synthesized via a solid-state method. Structural characterization revealed that both K⁺/Cl⁻ and K⁺/F⁻ co-doping reduced the Li_xNi_1−xO impurities and enlarged the lattice parameters compared to those of pure LNMO. Besides this, the K⁺/F⁻ co-doping decreased the Mn³⁺ ion content, which could inhibit the Jahn–Teller distortion and was beneficial to the cycling performance. Furthermore, both the K⁺/Cl⁻ and the K⁺/F⁻ co-doping reduced the particle size and made the particles more uniform. The K⁺/Cl⁻ co-doped particles possessed a similar octahedral structure to that of pure LNMO. In contrast, as the K⁺/F⁻ co-doping amount increased, the crystal structure became a truncated octahedral shape. The Li⁺ diffusion coefficient calculated from the CV tests showed that both K⁺/Cl⁻ and K⁺/F⁻ co-doping facilitated Li⁺ diffusion in the LNMO. The impedance tests showed that the charge transfer resistances were reduced by the co-doping. These results indicated that both the K⁺/Cl⁻ and the K⁺/F⁻ co-doping stabilized the crystal structures, facilitated Li⁺ diffusion, modified the particle morphologies, and increased the electrochemical kinetics. Benefiting from the unique advantages of the co-doping, the K⁺/Cl⁻ and K⁺/F⁻ co-doped samples exhibited improved rate and cycling performances. The K⁺/Cl⁻ co-doped Li_0.97K_0.03Ni_0.5Mn_1.5O_3.97Cl_0.03 (LNMO-KCl0.03) exhibited the best rate capability with discharge capacities of 116.1, 109.3, and 93.9 mAh g⁻¹ at high C-rates of 5C, 7C, and 10C, respectively. Moreover, the K⁺/F⁻ co-doped Li_0.98K_0.02Ni_0.5Mn_1.5O_3.98F_0.02 (LNMO-KF0.02) delivered excellent cycling stability, maintaining 85.8% of its initial discharge capacity after circulation for 500 cycles at 5C. Therefore, the K⁺/Cl⁻ or K⁺/F⁻ co-doping strategy proposed herein will play a significant role in the further construction of other high-voltage cathodes for high-energy LIBs.