All-solid-state lithium-ion batteries (ASSLBs) have become the core direction of the next-generation energy storage technology due to their high stability and high energy density potential. NASICON-type LATP (Li₁.₃Al₀.₃Ti₁.₇(PO₄)₃) solid electrolyte has attracted much attention due to its advantages of readily available raw materials and wide voltage window. However, the problems of uneven interfacial contact between particles and high grain boundary resistance have always restricted lithium ion transport efficiency and battery performance.
As a key factor affecting material interfacial interaction and transport characteristics, can particle size be the key to breaking this bottleneck? The research team prepared LATP solid electrolytes with different particle sizes through two synthesis methods, systematically exploring the effects of particle size effect on composite cathode structure, lithium ion conduction mechanism and battery electrochemical performance, providing a clear direction and experimental support for the performance optimization of all-solid-state batteries.
1. Experimental Design: Preparation and Comparison System of LATP with Two Particle Sizes
To accurately explore the influence of particle size, the research team prepared two types of LATP solid electrolytes with distinct characteristics through two classic synthesis methods, and built a complete comparative test system:
1. Preparation of LATP with Different Particle Sizes
Micron-scale LATP (LATP_SS): Synthesized by solid-state method, the particle size reaches several microns, the D50 value is about four times that of the nano-scale sample, the specific surface area is only 0.6276 m²g⁻¹, and the particle size is large with small specific surface area.
Nano-scale LATP (LATP_CP): Synthesized by co-precipitation method, the particle size is only a few hundred nanometers, the specific surface area is as high as 5.3687 m²g⁻¹, and the particles are fine with good dispersibility.
XRD tests confirmed that the target products were successfully synthesized in both types of samples without secondary crystalline phases, ensuring that the only experimental variable was the particle size difference.
2. Construction of Comparative Test System
Using high-nickel NCA as the active cathode material, combined with conductive carbon and PEO binder, composite cathodes were prepared with the two types of LATP respectively, and button-type all-solid-state lithium metal batteries were assembled. Through various technologies such as SEM, EDS, mercury porosimetry, EIS, CV, GITT, and in-situ XRD, comparative analysis was carried out from multiple dimensions including microstructure, pore characteristics, electrochemical performance, and structural stability.
2. Microstructure Duel: Nano-Scale LATP Builds a Better Transport Network
The microstructure and pore characteristics of the composite cathode directly determine the lithium ion transport efficiency, and the composite cathodes prepared with the two types of LATP show significant differences:
1. Particle Distribution and Interfacial Contact
LATP_SS composite cathode: FIB-SEM and EDS analysis show that micron-scale LATP particles are unevenly distributed in the cathode, there are obvious large gaps between particles and with NCA cathode materials, the interfacial contact area is limited, and it is difficult to form a continuous ion transport path.
LATP_CP composite cathode: Nano-scale LATP particles are uniformly dispersed in the cathode, there are no obvious gaps at the interfaces between particles, and the contact with NCA materials is more sufficient, providing dense interfacial channels for lithium ion transport.
2. Differences in Pore Characteristics
Mercury porosimetry results show that particle size is significantly related to the micropore characteristics of the composite cathode:
LATP_SS composite cathode: average pore size 0.39μm, porosity 25.2%, apparent density 2.06 gmL⁻¹;
LATP_CP composite cathode: average pore size 0.30μm, porosity 24.2%, apparent density 2.11 gmL⁻¹.
The smaller pore size and higher apparent density mean that the cathode structure is denser, and the lithium ion transport path is shorter, further improving the transport efficiency.
3. Electrochemical Performance Superiority: Nano-Scale LATP Achieves All-Dimensional Improvement
The advantages of microstructure are directly transformed into comprehensive leadership in electrochemical performance, and the battery assembled with nano-scale LATP performs better in all key indicators:
1. Ion Conduction Efficiency
At room temperature (25℃), the ionic conductivity of LATP_SS is 1.0×10⁻⁴ S cm⁻¹. Although LATP_CP has a slightly higher internal void due to shorter sintering time, its ionic conductivity is 0.45×10⁻⁴ S cm⁻¹, but in the composite cathode system, the advantage of its uniform distribution is more prominent;
Activation energy test shows that the activation energy of LATP_SS is 0.2344 eV, lower than 0.3126 eV of LATP_CP, indicating that the micron-scale LATP has smaller conduction resistance at the single particle level, but the influence of interfacial contact in the composite system is more critical.
2. Rate Performance and Discharge Capacity
At different current densities, the battery assembled with LATP_CP shows better rate adaptability:
At a current density of 18 mA g⁻¹, the discharge capacity of the LATP_CP battery reaches 170 mAh/g, higher than 160 mAh/g of the LATP_SS battery;
When the current density is increased to 180 mA g⁻¹, the gap further widens. The discharge capacity of the LATP_CP battery still maintains 106 mAh/g, while the LATP_SS battery is only 89 mAh/g, fully proving that the transport network built by nano-scale LATP is more suitable for high-current transport needs.
3. Cycle Stability and Coulombic Efficiency
Initial Coulombic efficiency: The LATP_CP battery reaches 84%, significantly higher than 70% of the LATP_SS battery, indicating better reversibility;
Long-cycle performance: After 100 cycles at 60℃ and 18 mA g⁻¹, the capacity retention rate of the LATP_CP battery reaches 65%, and the Coulombic efficiency is stable above 99%; while the capacity retention rate of the LATP_SS battery is only 50%, and the Coulombic efficiency is about 95%, with more obvious attenuation.
4. Polarization and Structural Stability
GITT test shows that the LATP_SS battery has larger internal resistance, the polarization difference before and after charging reaches 10 mV, and the polarization continues to increase with cycling; the LATP_CP battery has smaller polarization and smoother ion transport;
CV curves show that the intensity of the redox peaks of the LATP_SS battery decreases rapidly with cycling, and the irreversible reaction intensifies; while the peak shape of the LATP_CP battery changes slightly, with better structural stability;
In-situ XRD analysis confirms that the (003) peak of the NCA cathode in the LATP_CP battery moves less during charging, and the structural change above 4.1 V is slight, which significantly reduces the degradation degree of the cathode material.
4. Core Mechanism: How Does Particle Size Affect Lithium Ion Conduction?
The experimental results reveal the core mechanism of how LATP particle size affects the performance of all-solid-state batteries, which lies in the quality of the lithium ion transport network construction:
1. Shortcomings of Micron-Scale LATP
The larger particle size leads to: ① limited contact area with cathode materials and other electrolyte particles, forming “transport breakpoints”; ② long and uneven ion transport paths, leading to local current concentration; ③ many interfacial gaps, aggravating side reactions (such as PEO binder decomposition), further damaging the transport network and leading to rapid battery performance attenuation.
2. Advantages of Nano-Scale LATP
The small particle size brings: ① uniform dispersion to form dense interfacial contact, building a continuous and unobstructed lithium ion transport channel; ② short and uniformly distributed transport paths, reducing polarization and internal resistance; ③ inhibiting the occurrence of side reactions, protecting the structural stability of the cathode material, and extending the battery cycle life.
This mechanism indicates that in the composite cathode system, the “dispersion uniformity” and “interfacial contact quality” of electrolyte particles have a greater impact on performance than the intrinsic conduction efficiency of a single particle.
5. Research Significance: Providing a Clear Path for All-Solid-State Battery Optimization
Through systematic exploration of the particle size effect, this study provides key insights for improving the performance of all-solid-state lithium-ion batteries based on LATP:
Synthesis Strategy: Prioritize synthesis methods such as co-precipitation that can prepare nano-scale, highly dispersible LATP, and optimize the sintering process to reduce internal voids, balancing dispersibility and intrinsic conduction efficiency;
Cathode Design: Focus on the uniform dispersion of electrolyte particles in the composite cathode, maximize the interfacial contact area by reducing particle size and optimizing the ratio, and build an efficient lithium ion transport network;
Performance Optimization: For application requirements such as high rate and long cycle, nano-scale LATP is a better choice. Its advantages in transport efficiency and structural stability can better adapt to the high-performance requirements of all-solid-state batteries.
Conclusion
The particle size of LATP solid electrolyte has a decisive impact on the performance of all-solid-state lithium-ion batteries. Although nano-scale LATP is slightly inferior to micron-scale samples in the intrinsic ionic conductivity of single particles, it builds an efficient lithium ion transport network by virtue of more uniform dispersibility, more sufficient interfacial contact, and denser pore structure in the composite cathode, significantly improving the rate performance, cycle stability and structural stability of the battery.
This study not only reveals the correlation mechanism between solid electrolyte particle size and lithium ion conduction, but also provides a practical direction for electrolyte design and cathode optimization of all-solid-state batteries. In the future, by further optimizing the synthesis process of nano-scale LATP and reducing internal voids, it is expected to achieve the synergistic improvement of intrinsic conduction efficiency and dispersion performance, promoting all-solid-state lithium-ion batteries to develop towards higher energy density and longer life.
For more in-depth research on LATP solid electrolyte synthesis and all-solid-state battery performance optimization, you can refer to the research published by the Journal of Power Sources. Our previous articles on separator wettability and PVDF hierarchical porous membranes further elaborate on the development of battery materials and processes. For detailed industry standards and synthesis technologies, refer to the report released by the Institute of Electrical and Electronics Engineers (IEEE).