Abstract
All-solid-state batteries (ASSBs) face critical challenges, including the structural collapse of cathode active materials (CAMs) during cycling and interfacial instability between the sulfide-based solid electrolyte (SE) and the cathode, which leads to deteriorated electrochemical performance. Here, we report high-performance ASSBs enabled by localized titanium (Ti) doping and the formation of a Li4Ti5O12 (LTO) coating layer on CAMs, utilizing residual lithium (Li) components present on their surface as the Li source. The LTO offers a cost-effective, earth-abundant, and electrochemically stable alternative to LiNbO3. Ti incorporation into the LiNixCoyMn1-x-yO2 (NCM) lattice enhances the mechanical robustness of secondary particles by reinforcing their structural integrity. Moreover, the conformal LTO layer serves as a chemically stable interphase that effectively suppresses undesirable side reactions with sulfide-based SEs. The combination of Ti doping and LTO surface modification synergistically improves the mechanical integrity and interfacial stability of the electrode. As a result, ASSBs employing Ti-NCM@LTO with a high areal capacity of 8 mAh/cm2 exhibit enhanced electrochemical properties, including an initial capacity of 165.9 mAh/g, outstanding cycle stability of 83.4 % at 0.1C over 100 cycles, and a rate capability (reversible capacity) of 166.4, 148.4, 135.5, 130.4 and 119.4 mAh/g at 0.05, 0.1, 0.2, 0.5, and 1.0C, respectively.
| Original language | English |
|---|---|
| Article number | 100437 |
| Journal | eTransportation |
| Volume | 25 |
| DOIs | |
| State | Published - Sep 2025 |
| Externally published | Yes |
Funding
The surface morphology of bare NCM and Ti-NCM@LTO particles prepared with 10 ALD cycles was observed by SEM image. Bare NCM composed of primary particles approximately 700 nm in diameter exhibits spherical secondary spherical morphology with an average particle size of approximately 10 μm. The morphology of the NCM secondary particles was preserved after the ALD process, as shown in Fig. 2(a), (b), and (c). TEM measurements of bare NCM and Ti-NCM@LTO particles were taken to analyze the coating layer. Fig. 2(d) and (e) shows that the conformal coating layer with a thickness of ∼ 8 nm is observed on the Ti-NCM@LTO particles. To identify the crystal structure of the coating layer, the d-spacing was investigated by high-resolution TEM. The lattice inter-planar distances for the coating layer of regions (I) and (II) were 0.241 nm and 0.482 nm, corresponding to the LTO (222) plane and (111) plane, respectively [38,39]. Fig. 2(f) show elemental maps of the Ti-NCM@LTO particles. The titanium elements were uniformly distributed over the entire particle. To reveal the crystal structure of the Ti-NCM@LTO particles, XRD measurements of the samples were made. Fig. 2(g) and Fig. S9 shows that the (003) diffraction peaks of Ti-NCM@LTO shift to a lower angle, indicating lattice expansion caused by the Ti dopant [40]. In addition, HR-TEM analysis revealed that the d-spacing of the (003) plane increased from 0.472 nm (bare NCM) to 0.487 nm (Ti-NCM@LTO), supporting the conclusion that Ti doping was successfully incorporated into the NCM lattice structure (Fig. S10). Fig. S11 shows whole XRD patterns of the NCM particles prepared with different numbers of ALD cycles. All sample patterns exhibit the characteristic a layered α-NaFeO2 crystal structure, confirming that any change in the crystal structure after ALD was negligible. The ratio of peak intensity values between (003) and (104), denoted as I003/I104, indicates cation mixing between lithium and nickel ions. Typically, a ratio greater than 1.2 indicates the NCM material has a well-defined layered structure in the NCM material. The I003/I104 ratio values of bare NCM and Ti-NCM@LTO particles were 1.23 and 1.25, respectively. Both I003/I104 ratio values were larger than 1.2, implying that the layered structure was well maintained after ALD processing [41]. As the cycle number of TiO2 increases, the (003) diffraction peak shifts to lower angles, indicating successful lattice expansion due to the effective incorporation of Ti4+ as a dopant. The XPS measurements further analyzed the surface chemical composition of both samples. As shown in Fig. 2(h) the Ni 2p spectra of both samples are characterized by Ni 2p3/2 and Ni 2p1/2. The Ni 2p3/2 spectra exhibits two distinct peaks, located at approximately 854.8 eV and 855.9 eV, which are attributed to Ni2+ and Ni3+ oxidation states, respectively. A binding energy of Ti 2p is located at 458.4 eV, which corresponds with the Ti4+ oxidation state of the LTO material (Fig. 2(i)). This implies that a surface coating layer of LTO had formed on the surface of NCM, utilizing the impurity on the NCM as a raw material.S.L. and J.K. contributed equally to this work. This work was supported by the Ministry of Trade, Industry and Energy (MOTIE) of the Republic of Korea (Grant No. 20009985). This work was supported by the Human Resources Program in Energy Technology of the Korea Institute of Energy Technology Evaluation and Planning (KETEP), which was granted financial resources from the Ministry of Trade, Industry & Energy, Republic of Korea (No. 20214000000520). S.L. and J.K. contributed equally to this work. This work was supported by the Ministry of Trade, Industry and Energy ( MOTIE ) of the Republic of Korea (Grant No. 20009985 ). This work was supported by the Human Resources Program in Energy Technology of the Korea Institute of Energy Technology Evaluation and Planning ( KETEP ), which was granted financial resources from the Ministry of Trade, Industry & Energy, Republic of Korea (No. 20214000000520 ).
Keywords
- All-solid-state battery
- Cathode
- Protection layer
- Sulfide-based solid electrolyte