Recent Advances in Conduction Mechanisms, Synthesis Methods, and Improvement Strategies for Li_1+xAl_xTi_2−x(PO₄)₃ Solid Electrolyte for All‐Solid‐State Lithium Batteries

Abstract

With the increasing use of Li batteries for storage, their safety issues and energy densities are attracting considerable attention. Recently, replacing liquid organic electrolytes with solid‐state electrolytes (SSE) has been hailed as the key to developing safe and high‐energy‐density Li batteries. In particular, Li1+xAlxTi2−x(PO4)3 (LATP) has been identified as a very attractive SSE for Li batteries due to its excellent electrochemical stability, low production costs, and good chemical compatibility. However, interfacial reactions with electrodes and poor thermal stability at high temperatures severely restrict the practical use of LATP in solid‐state batteries (SSB). Herein, a systematic review of recent advances in LATP for SSBs is provided. This review starts with a brief introduction to the development history of LATP and then summarizes its structure, ion transport mechanism, and synthesis methods. Challenges (e.g., intrinsic brittleness, interfacial resistance, and compatibility) and corresponding solutions (ionic substitution, additives, protective layers, composite electrolytes, etc.) that are critical for practical applications are then discussed. Last, an outlook on the future research direction of LATP‐based SSB is provided.

Advancements in Quasi-Solid-State Li Batteries: A Rigid Hybrid Electrolyte Using LATP Porous Ceramic Membrane and Infiltrated Ionic Liquid

“…On the other hand, the inorganic ceramic solid electrolytes also result in attractive approaches due to the high voltage and thermal stability, compatibility with lithium metal, and fast Li + transport. − Several types of solid electrolytes have been investigated and, among them, Li 1+ x Ti 2– x Al x (PO 4 ) 3 (LATP) evidence promising properties such as high ionic conductivity (10 –4 –10 –3 S· –1 ), superior air stability, high oxidation voltage (∼6 V), and raw materials low prices . In general, the LATP ionic conductivity is governed by the microstructure, mainly grains and grain boundaries. , Hence, higher density and larger grain size are required to decrease the grain boundary impedance, which is achieved at sintering temperatures higher than 900 °C. , However, LATP has demonstrated modest electrochemical performance attributed to interfacial incompatibilities with the electrodes. , For instance, on the cathode side, apart from the low contact electrode–electrolyte, depletion of Li on the interface is observed due to migration to the cathode during charge . On the negative side, contact with metallic Li causes Ti 4+ reduction, generating a chemically unstable interface growth and cycling failure .…”

High-Entropy Laminates with High Ion Conductivities for High-Power All-Solid-State Lithium Metal Batteries

“…To solve the above problem of slow Li + transfer kinetics of the SSEs, a great deal of work is mainly focused on the exploration of enhancing the ionic conductivity by introducing aliovalent atoms into the crystal structure of inorganic SSEs. − Li 7 La 3 Zr 2 O 12 (LLZO), as a typical SSE, exhibits higher ionic conductivity (2.4 × 10 –4 S cm –1 ) in cubic phase than that of its counterpart in tetragonal phase (2.3 × 10 –5 S cm –1 ), while the cubic phase is unstable at room temperature. − Recently, many types of aliovalent ions (Ta 5+ , W 6+ , Te 6+ , and Nb 5+ ) are introduced into the crystal structure of LLZO, creating additional vacancies at Li + sites and further reducing the free energy of Li + transfer. , Through aliovalent atoms doping and vacancy regulation, Li 7– x La 3 Zr 2– x M x O 12 (M = Nb and Ta) delivers a higher ionic conductivity of 4 × 10 –4 S cm –1 than LLZO at room temperature, benefited from the stabilized phase with high conductivity and fast transport of lithium ions . However, current inorganic SSEs including LLZO and Li 1.3 Al 0.3 Ti 1.7 P 3 O 12 (LATP) are inevitably limited by their poor mechanical properties and complicated processing conditions, greatly hampering the practical applications. − On this occasion, polymers or their monomers are introduced into inorganic SSEs to fabricate composite electrolytes by physical-mechanical mixing, guaranteeing the ion transport properties and enhancing the mechanical strength to a certain extent. ,, For instance, poly­(propylene oxide) (PEO) elastomer is introduced into the LLZO, greatly improving its mechanical strength (∼1.0 MPa) and meanwhile improving the movement of PEO segments and the transport of Li + . However, the composite SSEs are usually fabricated by mixing inorganic filler, lithium salt, and polymer with physical-mechanical stirring, resulting in poor uniformity of inorganic filler and polymer and giving rise to unstable interfaces and Li + conductive channel between inorganic filler and polymer. , Moreover, due to the inferior chemically compatible of inorganic filler and polymer, the increments of mechanical strength and Li + conductivity are still limited. , Therefore, it is still a big challenge to develop a thin SSE with both high ionic conductivities and mechanical strength for ASSLMBs.…”

Stabilizing Li1.3Al0.3Ti1.7(PO4)3|Li Metal Anode Interface in Solid‐State Batteries by Kevlar Aramid Nanofiber‐Based Protective Coating

“…[9] Among the numerous classes of inorganic SSEs, including sodium super ionic conductor (NASICON), garnet, perovskite, and sulfide, [10] NASICON-type Li 1.3 Al 0.3 Ti 1.7 (PO 4 ) 3 (LATP) is considered particularly promising owing to its stability against H 2 O/CO 2 , high ionic conductivity (10 −4 -10 −3 S m −1 ) at room temperature, and facile synthesis with cost-efficient. [11] Despite the aforementioned merits, LATP is inherently flawed due to its susceptibility to reduction by metallic Li. [12] The direct physical contact between LATP and metallic Li gives rise to side reactions that generate reduction products possessing both electronic and ionic conductivities.…”

“…These products progressively degrade LATP, ultimately leading to battery failure. [11] Poor interface contact represents another serious rigid solid-materialrelated problem, with voids at the electrode|electrolyte interface that lead to high interfacial resistance and induce an inhomogeneous Li + flux during the Li deposition process, triggering uncontrollable dendritic growth. [13] Multiple approaches have been employed to address its interface challenges.…”