Amorphous Lithium Lanthanum Titanate for Solid-State Microbatteries

Abstract

Lithium lanthanum titanate (LLTO) is a promising solid state electrolyte for solid state batteries due to its demonstrated high bulk ionic conductivity. However, crystalline LLTO has a relatively low grain boundary conductivity, limiting the overall material conductivity. In this work, we investigate amorphous LLTO (a-LLTO) thin films grown by pulsed laser deposition (PLD). By controlling the background pressure and temperature we are able to optimize the ionic conductivity to 3 × 10 −4 S/cm and electronic conductivity to 5 × 10 −11 S/cm. XRD, TEM, and STEM/EELS analysis confirm that the films are amorphous and indicate that oxygen background gas is necessary during the PLD process to decrease the oxygen vacancy concentration, decreasing the electrical conductivity. Amorphous LLTO is deposited onto high voltage LiNi 0. Next generation lithium-ion batteries will require a broad range of energies to meet the challenges of portable electronic storage from electric vehicles to microelectromechanical systems (MEMS). The cost per Watt-hour of commercial batteries have shown incremental improvement due to better manufacturing design, but drastic increases in energy and power density are needed to satisfy projected demand. 1 Solid-state electrolytes are researched heavily because they have the potential to improve capacity loss, cycle lifetime, operation temperature, and safety. Lithium Phosphorous Oxynitride (LiPON) based thin-film solid-state batteries have excellent cycle life and are currently commercialized.2,3 However, LiPON has a relatively low ionic conductivity (1 × 10 −6 S/cm) and other solid electrolytes have demonstrated conductivity several orders of magnitude higher. 4,5 Lithium lanthanum titanate (LLTO) is a promising solid-state electrolyte due to its high bulk ionic conductivity (∼10 −3 S/cm) at room temperature, negligible electronic conductivity, and high voltage, atmospheric, and temperature stabilities.6-8 Extensive fundamental studies have been carried out to demonstrate this high ionic conductivity, elucidate the crystal structure, and determine the mechanism of lithium ion conduction.9-12 However, there are fundamental impediments to the implementation of crystalline LLTO into an actual device. One key issue is that crystalline LLTO has a relatively low grain boundary ionic conductivity (<10 −5 S/cm), lowering the effective material ionic conductivity. 6 In addition, crystalline LLTO is unstable in contact with lithium metal because lithium will easily insert reducing Ti 4+ to Ti 3+ , thus increasing electronic conductivity. 13,14Fortunately, amorphous LLTO has not only been shown to overcome these barriers, the lower energy constraints of fabricating amorphous LLTO opens up numerous thin film synthesis techniques. Amorphous LLTO thin films have been synthesized by pulsed laser deposition (PLD), RF magnetron sputtering, E-beam evaporation, atomic layer deposition, chemical solution deposition and sol-gel synthesis. [15][16][17][18][19][20][21][22][23][24] Furusawa et al. demonstrated amorphous LL...

Pulsed Laser Deposited Films for Microbatteries

“…PLD LLTO films with a σi of 3 × 10 −4 S·cm −1 and σe of 5 × 10 −11 S·cm −1 were obtained by controlling the background PO₂ and Ts. Amorphous LLTO films were utilized in SSMB cycled up to 4.8 V vs. Li + /Li with high voltage LiNi0.5Mn1.5O4 spinel cathode thin films [274].…”

Pulsed Laser Deposition‐based Thin Film Microbatteries

“…[93] The electrical conductivity of amorphous LLTO was shown to be highly dependent on the oxygen pressure in the chamber, as minimising oxygen vacancies is key to minimising electrical conductivity. [94] [96] related studies on Li 0.5 La 0.5 TiO 2 [97] and antiperovskite compositions of Li-rich Li 3 OCl which showed that the PLD films can produce ionic conductivities an order of magnitude higher than the bulk versions of these films. [98] A similar observation of film versus bulk performance were made for certain garnets such as PLD grown Li 7 La 3 Zr 2 O 12 and in this case better stability against Li metal was also found.…”

“…Further work illustrated how a step of rapid annealing of the entire stacked growth to 700 °C for 5 mins can result in better capacity retention and this was associated with the how the interface evolved or was modified during annealing . The electrical conductivity of amorphous LLTO was shown to be highly dependent on the oxygen pressure in the chamber, as minimising oxygen vacancies is key to minimising electrical conductivity . Other perovskite compositions explored using PLD include Li 0.33 La 0.56 TiO 3 , Li 0.17 La 0.61 TiO 3 related studies on Li 0.5 La 0.5 TiO 2 and anti‐perovskite compositions of Li‐rich Li 3 OCl which showed that the PLD films can produce ionic conductivities an order of magnitude higher than the bulk versions of these films…”

A Simple and Fast Electrochemical CO2 Sensor Based on Li7La3Zr2O12 for Environmental Monitoring

“…One of the strategies to improve electrochemical sensors' attractiveness for applications in terms of low power consumption and fast response time would be to promote higher Li + mobility at TPBs and between the solid electrolyte and the auxiliary phase. There have been successful attempts of using very fast ceramic Li‐conductors, such as Li 3 x La ((2/3)− x ) □ ((1/3)−2 x ) TiO 3 (1 × 10 −3 S cm −1 ) for CO 2 tracking . Lithium lanthanum titanate based devices show however phase stability issues due to reduction of Ti.…”