Solid-state Batteries Research Articles

How dispersed LLZTO enhances ionic conductivity in LiFePO4 composite cathodes for solid-state batteries

To improve the ionic conductivity of the LiFePO4 cathode for high-performance solid-state lithium-ion batteries, we incorporated the chemically stable and ion-conductive Li6.75La3Zr1.75Ta0.25O12 (LLZTO) into the cathode. We discovered that the impact of this incorporation on enhancing conductivity was influenced by how well the LLZTO particles were dispersed. A solid-state battery constructed with the LiFePO4 cathode without any LLZTO incorporated exhibited an initial capacity of 146 mAh g−1 at 0.2C, with a retention of 26 % after 100 cycles of charge-discharge. When the cathode was incorporated with LLZTO particles in their original agglomerated state, the initial capacity remained similar to the pristine one, but the retention decreased to <20 %. However, when LLZTO was well-dispersed during incorporation, the initial capacity increased to 160 mAh g−1, and retention improved to over 95 %. The difference in the effectiveness of incorporating dispersed and agglomerated LLZTO on the electrochemical performance has been clarified to be mainly related to the polarization of Li+ during transport in the cathodes. This was elucidated by numerical simulations based on finite element analysis, which revealed that incorporating LLZTO agglomerates leads to a deficiency of Li+ transport in specific regions within the LiFePO4 cathode and non-uniform Li+ transport through LLZTO, resulting in reduced overall cathode conductivity and battery performance.

Efficient sodium ion transport enhanced by anionophilic sites in polymer-supported plastic crystal electrolyte for high performance sodium metal anode

The design of sodium metal batteries (SMBs) is seen as an excellent solution to solve the request of next-generation energy storage technologies with high energy density, high safety, low cost, and environmental friendliness. However, the direct use of sodium metal as an anode produces the dendritic sodium, which harms the normal operation of battery. Inspired by solid-state lithium metal batteries, solid-state electrolyte (SSE) designed for SMBs effectively solves this shortcoming. Herein, a novel SSE with mask-based polymer membrane supporting plastic crystal electrolyte with ZIF-67 (MPPZ) is designed. The experimental results and density functional theory (DFT) calculations indicate that the addition of ZIF-67 in MPPZ electrolyte availably fixes TFSI− and achieves high Na+ transference number. Additionally, a protective layer of NaF is formed in situ on the surface of sodium metal to avoid side reactions between Na and MPPZ electrolyte while further guide the uniform deposition of Na. Accordingly, Na||Na symmetric battery with NaF-coated Na metal anode and MPPZ electrolyte has a stable deposition and stripping of Na for 3000 h. The assembled room temperature solid-state sodium-sulfur battery (RTSSSSB) exhibits a good cycle stability. This study provides an innovative thinking for the construction of high performance dendrite-free SMBs.

In Situ Constructing Robust Interface by Deep Eutectic Polymeric Electrolyte Enables High Performance Lithium Metal Batteries with High-Loading Cathode.

The low Li+ transport and poor interface have consistently been two major impediments to practical applications of Polyacrylonitrile (PAN)-based composite solid-state electrolytes (PCPE). In this work, a polymerizable deep eutectic electrolyte is meticulously designed with high fluidity which consists of Poly (Ethylene Glycol) Diacrylate (PEGDA), Fluoroethylene Carbonate (FEC), Succinonitrile (SN) and dual salts (LiTFSI/LiDFOB) to promote Li+ transport and ameliorate the interface of PCPE. Inclusion of PEGDA monomers and FEC alters the crystallinity of SN, enhancing the wettability of thick electrode, and formation of polymeric 3D network from polymerization of PEGDA can anchor SN and suppress the side reactions between SN and lithium metal. Consequently, the modified PCPE exhibit an enhanced conductivity of 4.47×10-4Scm-1 with Li-ion transference number of 0.60, and show an excellent lithium stability. LiCoO2(LCO)/SP-PCPE/Li batteries with higher loading (3-4.4V, 6mgcm-2) can work for over 300 cycles at 0.5 C. Even with an ultra-high loading of 16mgcm-2, LCO/SP-PCPE/Li batteries achieve an excellent cycling performance. This work provides new insights into how to construct a robust interface for solid-state batteries with high-loading cathode.

Unveiling the Role of Filler Characteristics in Enhancing the High-Voltage Performance of Succinonitrile-Based Solid-State Lithium-Metal Batteries.

For exploiting high-energy lithium-metal batteries, it is of utmost importance to develop electrolytes that possess exceptional ionic conductivity and an extensive electrochemical stability range. In this study, 3D PAN nanofibers and polymer electrolytes incorporating various inorganic fillers with different Lewis acid-base properties were fabricated. PAN@Al-SSE exhibits exceptional ionic conductivity (0.48 mS·cm-2 at room temperature), a high Li+ transference number (0.41), and a wide electrochemical window (5.26 V). The device is able to operate stably in Li symmetric cells for more than 1000 h under a potential of 0.03 V under a current density of 0.2 mA·cm-2. Besides, the groundbreaking technology equips high-voltage Li-LiCoO2 solid-state batteries with exceptional cycling performance (91.3% and 82.1% retention after 100 cycles at 0.2 and 1 C, respectively) at room temperature. Mechanistic studies indicate that the Lewis acid-base properties of surface fillers are instrumental and crucial to form a stable solid-electrolyte interphase layer. γ-Al2O3, in particular, with more Lewis acid sites, ensures the dissociation of LiTFSI and induces the excessive decomposition and polymerization of succinonitrile. There exists an equilibrium effect between dissociation and polymerization in a succinonitrile-based solid electrolyte, which plays a critical role in improving the manifestation of succinonitrile-based solid-state lithium cells, especially under high-voltage conditions.

A Piezocatalysis Strategy to Enable Efficient Redox in Solid-State Battery.

Piezocatalysis is considered to be a favorable catalytic technology by utilizing external mechanical stimulation to promote the specific redox reactions. The application of piezocatalysis in batteries is promising but faces formidable challenges. Herein, the operation principles of piezocatalysis were successfully demonstrated by constructing a solid-state Li-Se (S) battery model with interfacial stress accumulation. Lead zirconate titanate with an ultra-high piezoelectric coefficient was applied as the piezoelectric catalyst. The uniformity of the dipole orientation in materials was essential for achieving piezocatalysis in batteries. The accumulated high-stress converts to piezopotential for catalyzing most reaction processes in batteries, while the rapid stress change prevents the internal charge reorganization, ensuring continuous efficient catalysis. The internal stress change alters the internal polarisation strength, driving excess screening charge to participate in the electrochemical reaction. Under piezocatalysis, solid-state Li-Se batteries exhibited a initial discharge capacity of 670.9 mAh g-1 (99.4% of the theoretical value) at 0.1C, and Li-S batteries showed a capacity of 1463 mAh g-1 at 0.2C, which was still maintained up to 1084 mAh g-1 at an elevated rate of 0.5C. This piezocatalysis strategy provides a strong theoretical basis and design specification for enhancing Li-Se (S) cell reaction kinetics.

Improved solid-state lithium-ion battery on stainless steel substrate with graphene nanowalls by microwave plasma-enhanced chemical vapor deposition

Improved solid-state lithium-ion battery on stainless steel substrate with graphene nanowalls by microwave plasma-enhanced chemical vapor deposition

Electric Field and Nanocontact Effects in Metal-Organic Framework/Li6.4La3Zr1.4Ta0.6O12 Ionic Conductors for Fast Interfacial Lithium-Ion Transport Kinetics.

The slow ion transport kinetics inside or between the nanofillers in composite polymer electrolytes (CPEs) lead to the formation of lithium dendrites for solid-state lithium batteries. To address the critical issues, CPEs (U@UNL) composed of a UIO-66@UIO-66-NH2 (U@UN) core-shell heterostructure and Li6.4La3Zr1.4Ta0.6O12 (LLZTO) filler is designed. Due to the different band structures of the U@UN heterostructure, a built-in electric field is constructed to promote the transfer kinetics of carriers. Besides, the introduction of LLZTO facilitates the formation of a close nanometer contact interface between U@UN and LLZTO, reducing interface impedance and accelerating the lithium-ion transfer rate. As a benefit from the built-in electric field and the nanometer contact interface, U@UNL exhibits a wide electrochemical window of 5.17 V, a large lithium-ion transference number of 0.76, and a high ionic conductivity of 3.50 × 10-3 S cm-1. Consequently, the U@UNL electrolyte possesses excellent interfacial stability against Li metal after 1200 h at 0.1 mA cm-2 and shows a high specific capacity of 160.2 and 152.6 mAh g-1 at 0.5 and 1 C, respectively. This work proposes a complete strategy for building high-performance solid-state lithium batteries by a built-in electric field and nanometer contact interface between U@UN and LLZTO.

Bilayer Heterostructure Electrolytes Were Prepared by a UV-Curing Process for High Temperature Lithium-Ion Batteries

Solid-state electrolytes are widely anticipated to revitalize high-energy-density and high-safety lithium-ion batteries. However, low ionic conductivity and high interfacial resistance at room temperature pose challenges for their practical application. In this work, the dual-matrix concept is applied to the design of a bilayer heterogeneous structure. The electrolyte in contact with the cathode blends PVDF-HFP and oxidation-resistant PAN. In contrast, the electrolyte in contact with the anode blends PVDF-HFP and reduction-resistant PEO. A UV-curing process was used to fabricate the bilayer heterostructure electrolyte. The heterostructure electrolyte exhibits an ionic conductivity of 4.27 × 10−4 S/cm and a Li+ transference number of 0.68 at room temperature. Additionally, when assembled into LiFePO4/CPEs/Li batteries, it shows a high initial discharge capacity at room temperature (168 mAh g−1 at 0.1 C and 60 mAh g−1 at 2 C), with a capacity retention of 93.3% after 100 cycles at a current density of 0.2 C. Notably, at 60 °C, the battery maintains a discharge capacity of 90 mAh g−1 at 2 C, with a capacity retention of 97.4% after 100 cycles at 0.2 C. Therefore, solid-state batteries using this bilayer heterogeneous structure electrolyte demonstrate promising performance, including effective capacity output and cycling stability.

Strong Lewis-acid coordinated PEO electrolyte achieves 4.8 V-class all-solid-state batteries over 580 Wh kg−1

Polyethylene oxide (PEO) based electrolytes critically govern the security and energy density of solid-state batteries, but typically suffer from poor oxidation resistance at high voltages, which limits the energy density of batteries. Here, we report a Lewis-acid coordinated strategy to significantly improve the cyclic stability of 4.8 V-class PEO-based battery. The introduced Mg2+ and Al3+ with strong electron-withdrawing capability weaken the electron density of ether oxygen (EO) chains via chelation in the coordination structure, resulting in a locally limited interaction between the EO chains and the surface of cathodes at high state of charge. The batteries using Lewis-acid coordinated electrolytes and Ni-rich cathodes achieve high voltage stability of 4.8 V over 300 cycles. Further, the realization of industrial-scale electrolyte membranes, and Ah-level pouch cells over 586 Wh kg‒1 with good cyclic stability, suggests the potential of our strategy in practical applications of all-solid-state batteries.

Achieving Higher Critical Current Density in LGPS-Based Lithium Metal Batteries via a Synergistic Interlayer for Physical Inhibition and Chemical Scavenging of Lithium Dendrites.

Li10.35Ge1.35P1.65S12 (LGPS) electrolyte has garnered attention due to its high ionic conductivity and processability. However, its strong incompatibility with lithium metal hinders its practical application. Conventional interlayer strategy isolates Li from LGPS, avoiding the detrimental side reactions, but lithium dendrite penetration is still a problem. To address the aforementioned challenges, we develop a PVDF-HFP-supported PDOL-based interlayer (PDOL/PVDF-HFP), which stabilizes the LGPS/Li interface by synergistically physically inhibiting and chemically scavenging lithium dendrites. The multifunctional feature of the interlayer comes from the use of a bifunctional initiator, InCl3. On the one hand, InCl3 induces the polymerization of DOL, forming a physical separator and protecting lithium from LGPS; on the other hand, in situ reactions between In3+/Cl- and Li form a LiCl/LiF/LiIn hybrid SEI, homogenizing the surface Li+ flux and suppressing lithium dendrite formation and penetration. In addition, an unexpected dynamic microdendrite scavenging is realized by virtue of the side reactions of LGPS/Li, which converts the undesirable reaction to be an advantage in our design. Benefiting from the comprehensive advantages of such design, the constructed sulfide-based solid-state batteries achieve a super low interfacial impedance of 5.1 Ω, a high critical current density (CCD) value over 5 mA/cm2, and a super long cycling stability over 8000 h. Our synergistic interlayer strategy would open an effective avenue for solving interfacial challenges for practical sulfide-based solid-state batteries.

Re-evaluating critical current density in solid-state batteries: Challenges and proposing an alternative

The critical current density (CCD) test protocols are widely adopted to examine the quality of solid electrolyte (SE), the stability of lithium (Li)/SE interfaces, and solid-solid interfacial kinetics in all solid-state lithium batteries (SSLBs). This work systematically investigated the impact of major experimental parameters on CCD values of Li symmetric cells using argyrodite Li6PS5Cl SE. Four categories of experimental parameters were investigated: (i) SE parameters, (ii) Li metal parameters, (iii) cell die parameters, and (iv) CCD testing protocols. Each parameter uniquely influences the density of the SE or the SE/Li interface, thereby affecting the resulting CCD values. Notably, CCD values are highly dependent on the cell operating histories, particularly the operating period (h) and the applied current density (mA/cm2). Consequently, without standardizing and unifying CCD testing protocols, obtaining reliable and repeatable CCD values remain challenging. To overcome this limitation, we propose the cumulative areal capacity (CAC) test protocol – the total capacity (mAh/cm2) delivered by a cell before its failure – as a more accurate measure of cell performance. CAC analysis of over 30 Li symmetric cells demonstrated statistical convergence in CAC values, highlighting its potential as a supplementary or even alternative testing protocol to conventional CCD methods.

Constructing high performance dry-processing oxide composite electrolyte via interfacial interactions for durable solid-state lithium batteries

Composite solid electrolytes (CSEs) have considerable combination properties, which have been considered as the most promising choice for realizing advanced solid-state lithium batteries. Yet the ionic conductivity of CSEs fails to meet the practical requirements. Herein, we develop a dry-processing CSEs based on Li1.5Al0.5Ge1.5(PO4)3 (LAGP) and succinonitrile (SN) through polytetrafluoroethylene fibrillation. On the one hand, SN can enable fast ion transport in ceramic network and serve as high-speed conducive path. On the other hand, the strong affinities of LAGP towards SN and anions can significantly improve the conductive behavior and restrict side reactions at electrolyte/Li interface. Under such regulations, the composite electrolyte exhibits high ionic conductivity (0.64 mS cm−1 at 30 °C), high transference number (0.50), and high oxidation potential (>5.0V vs. Li+/Li). The assembled lithium metal batteries demonstrate excellent stability over 300 cycles at 1.0C. This work demonstrates the ion migration mechanism and the interactions at the heterogeneous interface for SN enhanced CSEs, contributing to the development of durable solid lithium metal batteries with extended lifespan.

Solid-State Lithium Batteries with In Situ Polymerized Acrylate-Based Electrolytes Capable of Electrochemically Stable Operation at 100 °C.

Solid polymer electrolytes (SPEs) typically consist of salts with mobile anions that could cause instabilities and parasitic side reactions in solid-state lithium (Li) batteries. To address this challenge, single-Li-ion conducting (SLIC) SPEs, where anions of Li salts are covalently attached to the polymer backbone, have been utilized to reduce the number of mobile anions. This approach improves the cationic transference number but is accompanied by a loss of ionic conductivity. In this work, we investigate a synergetic approach of using both a polymerizable SLIC salt and a conventional Li salt in a polymer matrix by in situ polymerization of the poly(propylene glycol) acrylate (PPGA) monomer. The synthesized hybrid SPEs show a high ionic conductivity of up to ∼2 × 10-4 S cm-1 and a relatively high Li-ion transference number of ∼0.4. With a significantly reduced fraction of mobile anions in the combined salt SPE, in situ polymerized SPE cells with a LiFePO4 (LFP) cathode achieve a stable performance for over 100 cycles at temperatures as high as 100 °C, which is unattainable with conventional Li salts or electrolytes. Furthermore, solid-state nuclear magnetic resonance spectra provide additional insights into differences in Li nucleus environments and emphasize a reduction in activation energy for hybrid SPEs due to their more open structure. This study opens the path for the fabrication of high-performance solid polymer Li batteries capable of operating at high temperatures using commercial battery fabrication equipment, as in situ polymerized acrylate-based polymers provide drop-in compatibility with conventional battery production, ease of acrylate polymerization, and inexpensive, facile SPE chemistry. We expect that further tuning of the acrylate-based SPE composition may allow further increases in its conductivity without sacrificing its electrochemical stability or mechanical properties.

Li2FeCl4 as a Cost-Effective and Durable Cathode for Solid-State Li-Ion Batteries

Li₂FeCl₄ as a Cost-Effective and Durable Cathode for Solid-State Li-Ion Batteries

Organic Cationic-Coordinated Perfluoropolymer Electrolytes with Strong Li+-Solvent Interaction for Solid State Li-Metal Batteries.

The practical application of solid-state polymer lithium-metal batteries (LMBs) is plagued by the inferior ionic conductivity of the applied polymer electrolytes (PEs), which is caused by the coupling of ion transport with the motion of polymer segments. Here, solvated molecules based on ionic liquid and lithium salt with strong Li+-solvent interaction are inserted into an elaborately engineered perfluoropolymer electrolyte via ionic dipole interaction, extensively facilitating Li+ transport and improving mechanical properties. The intensified formation of solvation structures of contact ion pairs and ionic aggregates, as well as the strong electron-withdrawal properties of the F atoms in perfluoropolymers, give the PE high electrochemical stability and excellent interfacial stability. As a result, Li||Li symmetric cells demonstrate a lifetime of 2500 h and an exceptionally high critical current density above 2.3 mA cm-2, Li||LiFePO4 batteries exhibit consistent cycling for 550 cycles at 10 C, and Li||uncoated LiNi0.8Co0.1Mn0.1O2 cells achieve 1000 cycles at 0.5 C with an average Coulombic efficiency of 98.45 %, one of the best results reported to date based on PEs. Our discovery sheds fresh light on the targeted synergistic regulation of the electro-chemo-mechanical properties of PEs to extend the cycle life of LMBs.

Stabilizing the Bilateral Interfaces by a PVDF-Based Double-Layer Solid Composite Electrolyte with a Relieved Dehydrofluorination Effect for Solid-State Lithium Metal Batteries.

The dehydrofluorination effect of poly(vinylidene fluoride) (PVDF) induced by ceramic fillers with an alkaline surface compromises the comprehensive properties of the solid composite electrolyte (SCE) and leads to the deficient performance of the solid-state lithium metal batteries (SLMBs). In this work, a unique PVDF-based double-layer solid electrolyte was fabricated, which consisted of a Li6.4La3Zr1.4Ta0.6O12 (LLZTO)-filled SCE with poly(acrylic acid) (PAA) as an alkalinity-scavenging agent in contact with the Li anode, and another SCE with lithium difluoro(oxalato)borate (LiDFOB) as a film-formation additive facing the cathode. It is found that a moderate amount of PAA relieves the dehydrofluorination degree of the PVDF matrix and improves the Li plating/stripping reversibility, and the addition of LiDFOB is involved in the formation of a stable passivation film on the cathode. Consequently, the resultant double-layer SCE holds favorable overall properties, especially being well-compatible with both electrodes, endowing the SLMBs with superior cycle and rate performance at room temperature.

Synergistic effect of ceramic filler in polymer salt complex for improved ion dissociation and migration mechanism

Abstract Use of Ceramic filler is one of the most common approaches to improve the conductivity and stability properties of a solid polymer electrolyte (SPE) cum separator. Among them, active fillers like Garnet have been extensively used to enhance the stability and conductivity of SPE. However, SPE suffers from limited ion migration at room temperature acting as a bottleneck for their application in all solid-state batteries. An extensive study on these fillers' role in ion dissociation and migration can be a stepping stone for advanced SPE. In the present work, an FTIR analysis has primarily been used to identify and evaluate cation coordinate site-cation, and ion pair interactions in a Li6.5La3Zr1.75Te0.25O12 loaded polyethylene oxide-LiCF3SO3 matrix with varying ceramic concentrations. Further, the Trukhan model has been used to calculate diffusion coefficient, mobility, and charge carrier density to interpret relaxation parameters, conductivity, and FTIR results in the SPE samples. Finally, an ion migration model has been proposed based on the results obtained in experimental studies.&amp;#xD;

Fabrication of Scalable Covalent Organic Framework Membrane-based Electrolytes for Solid-State Lithium Metal Batteries.

The conventional covalent organic framework (COF)-based electrolytes with tailored ionic conducting behaviors are typically fabricated in the powder morphology, requiring further compaction procedures to operate as solid electrolyte tablets, which hinders the large-scale manufacturing of COF materials. In this study, we present a feasible electrospinning strategy to prepare scalable, self-supporting COF membranes (COMs) that feature a rigid COF skeleton bonded with flexible, lithiophilic polyethylene glycol (PEG) chains, forming an ion conduction network for Li+ transport. The resulting PEG-COM electrolytes exhibit enhanced dendrite inhibition and high ionic conductivity of 0.153 mS cm-1 at 30 °C. The improved Li+ conduction in PEG-COM electrolytes stems from the loose ion pairing in the structure and the production of higher free Li+ content, as confirmed by solid-state 7Li NMR experiments. These changes in the local microenvironment of Li+ facilitate its directional movement within the COM pores. Consequently, solid-state symmetrical Li|Li, Li|LFP, and pouch cells demonstrate excellent electrochemical performance at 60 °C. This strategy offers a universal approach for constructing scalable COM-based electrolytes, thereby broadening the practical applications of COFs in solid-state lithium metal batteries.

Probing degradation at solid-state battery interfaces using machine-learning interatomic potential

Solid-state batteries featuring fast ion-conducting solid electrolytes are promising next-generation energy storage technologies, yet challenges remain for practical deployment due to electro-chemo-mechanical instabilities at solid-solid interfaces. These interfaces, which include homogeneous/internal interfaces such as grain boundaries (GBs) and heterogeneous/external interfaces between solid-electrolyte and electrode materials, can impede Li-ion transport, deteriorate performance, and eventually lead to cell failure. Here we leverage large-scale molecular simulations, enabled by validated machine-learning interatomic potentials, to directly probe the onset of interfacial degradation at the garnet Li7La3Zr2O12 (LLZO) solid-electrolyte/LiCoO2 (LCO) cathode interface. By surveying different interfacial geometries and compositions, it is found that Li-deficient interfaces can lead to severe interfacial disordering with cation mixing and Co interdiffusion from LCO into LLZO. By contrast, Li-sufficient interfaces are less disordered, although elemental segregation with local ordering is observed. As a consequence of Co interdiffusion, Co-rich regions are formed at the GBs of LLZO due to cation segregation and trapping effects. This behavior is independent of the GB tilting axis, degree of disorder at the GBs, and Co concentration, which implies Co clustering at GBs is a general phenomenon in polycrystalline LLZO and can dictate its overall transport and mechanical properties. Our findings elucidate the underlying fundamental mechanisms that give rise to experimentally observed physicochemical properties and provide guidelines for interface design that can mitigate interfacial degradation and improve cycling performance.

Garnet-Type Zinc Hexacyanoferrates as Lithium, Sodium, and Potassium Solid Electrolytes

Sodium-ion batteries offer an attractive alternative to lithium-based chemistries due to the lower cost and abundance of sodium compared to lithium. Using solid electrolytes instead of liquid ones in such batteries may help improve safety and energy density, but they need to combine easy processing with high stability toward the electrodes. Herein, we describe a new class of solid electrolytes that are accessible by room-temperature, aqueous synthesis. The materials exhibit a garnet-type zinc hexacyanoferrate framework with large diffusion channels for alkaline ions. Specifically, they show superionic behavior and allow for facile processing into pellets. We compare the structure, stability, and transport properties of lithium-, sodium-, and potassium-containing zinc hexacyanoferrates and find that Na2Zn3[Fe(CN)6]2 achieves the highest ionic conductivity of up to 0.21 mS/cm at room temperature. In addition, the electrochemical performance and stability of the latter solid electrolyte are examined in solid-state sodium-ion batteries.