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Exploits, advances and challenges benefiting beyond Li-ion battery technologies

A. El Kharbachi, O. Zavorotynska, M. Latroche, F. Cuevas, V. Yartys, M. Fichtner

arXiv:2005.04963v1physics.app-phcond-mat.mtrl-sci

TL;DR

The paper addresses how battery technologies beyond Li-ion can respond to expanding demands from electric vehicles, energy storage, and other applications amid Li-ion resource and performance constraints. It reviews cationic and anionic shuttle chemistries and MH-based batteries, compares their challenges and prospects, and concludes that aqueous systems merit reconsideration for cost-effective, safer applications such as quasi-stationary storage.

  • Problem

    Li-ion batteries face limited lithium resources and constraints in meeting the performance, cost, and safety requirements of large-scale applications.

  • Method

    The paper reviews post-Li-ion cationic and anionic shuttle batteries, MH-based batteries, relevant materials and electrolytes, and application-specific research challenges.

  • Results

    The review compares battery systems with Li-ion assumptions and identifies aqueous systems as candidates for cost-effective and safer applications, while Na-ion performance is approaching that of Li-ion.

  • Takeaways & Limitations

    Aqueous systems merit reconsideration for intensive battery production and quasi-stationary energy-storage applications.

  • Takeaways & Limitations

    Assessing post-Li-ion performance remains constrained by the difficulty of evaluating end-of-life energy for full cells.

Abstract

from arXiv · show

The battery market is undergoing quick expansion owing to the urgent demand for mobile devices, electric vehicles and energy storage systems, convoying the current energy transition. Beyond Li-ion batteries are of high importance to follow these multiple-speed changes and adapt to the specificity of each application. This review-study will address some of the relevant post-Li ion issues and battery technologies, including Na-ion batteries, Mg batteries, Ca-ion batteries, Zn-ion batteries, Al-ion batteries and anionic (F- and Cl-) shuttle batteries. MH-based batteries are also presented with emphasize on NiMH batteries, and novel MH-accommodated Li-ion batteries. Finally, to facilitate further research and development some future research trends and directions are discussed based on comparison of the different battery systems with respect to Li-ion battery assumptions. Remarkably, aqueous systems are most likely to be given reconsideration for intensive, cost-effective and safer production of batteries; for instance to be utilized in (quasi)-stationary energy storage applications.

1. Introduction

Rapid growth in electric vehicles, energy storage, and mobile applications is increasing demand for batteries, while conventional Li-ion systems face resource, cost, performance, and safety constraints. The review surveys post-Li-ion chemistries and MH-based systems, then discusses challenges and research directions for application-specific battery development.

  • Challenges: Limited lithium resources and safety factors are expected to constrain LIB use in large-scale applications.Long-term supply may depend on political decisions, while supply-demand gaps could produce significant price fluctuations despite recycling and new sources.
  • Motivation: Battery markets are expanding from small-scale mobile applications toward large-capacity electric-vehicle and energy-storage sectors.The expansion is linked to emerging applications, smart grids, and renewable-energy integration.
  • Motivation: LIBs face difficulties meeting electric-vehicle and grid-storage needs for high energy density, long range, low cost, and safety.Adding battery stacks does not resolve long-range or excessive-cost issues, while grid storage requires inexpensive production and output modulation.
  • Alternatives: Sodium- and potassium-ion batteries use relatively abundant, inexpensive elements with chemical similarities to lithium but currently have lower energy density and electrolyte-related drawbacks.Reported concerns include highly toxic and flammable electrolytes, high early-stage operating costs, and greater operational complexity for SIBs.
  • Scope: The review surveys Na, Mg, Ca, Zn, and Al cationic shuttles, halide anionic shuttles, NiMH batteries, and metal-hydride-accommodated LIBs.It also considers electrode materials, electrolytes, scientific challenges, application specificity, and future research directions.

2.1. Monovalent systems: Na-ion batteries

Na-ion batteries are being developed as lower-cost, potentially safer alternatives to Li-ion systems, but their lower capacities and energy densities, structural changes, and unresolved degradation limit rapid deployment. Progress spans hard-carbon anodes, transition-metal oxide and polyanionic cathodes, electrolyte engineering, and aqueous systems.

  • Motivation and current development: Na-ion batteries offer abundant sodium, potentially lower costs, reduced thermal runaway, and possible adaptation of Li-ion manufacturing processes.Their cost advantage is not assured when normalized to energy density, and existing Li-ion systems remain more competitive in high-energy applications.
  • Motivation and current development: Lower theoretical capacities and energy densities than Li-ion batteries constrain Na-ion cells, while larger Na ions prevent graphite intercalation and favor hard-carbon anodes.Hard carbon is described as the most suitable anode for SIBs.
  • Cathode materials: Na(Ni0.5Mn0.5)O2 delivers 125 mAh.g-1 between 2.2-3.8 V with high rate capability, but layered oxides face long-term cycling challenges from structural volume changes.These changes arise during Na+ (de)intercalation.
  • Cathode materials: 185 mAh.g-1 at C/10 and 71% retention over 20 cycles were reported for α-NaMnO2, with 70% retention after 100 cycles relative to the β-phase.Its charge–discharge profile contains multiple steps associated with intermediate-phase transformations whose pathways remain incompletely understood.
  • Cathode materials: Electrolyte substitution with 1M NaBF4/TEGDME improves α-NaMnO2 long-term cyclability by stabilizing interface resistance.The EC:DEC electrolyte instead provides lower bulk and interfacial resistances.
  • Cathode materials: NaNi0.5Ti0.5O2 shows reversible structural behavior, 3.1 V average voltage, 121 mAh g-1 at C/5, 60% initial capacity at 5C, and 27 mAh g-1 at 10C.The electrode also exhibits good cyclability and stability over 100 cycles at C/5 and 1C.

2.2.1. Mg batteries

Mg batteries benefit from magnesium’s high-capacity, dendrite-free metal anode and potential economic and sustainability advantages, but electrolyte–cathode–anode compatibility remains a central challenge. Research has improved electrolyte stability, Mg deposition, and cathode performance, while sluggish and temperature-dependent Mg2+ intercalation still constrains practical cells.

  • Motivation, principle and historical development: Magnesium metal offers theoretical capacities of 2200 mAh g-1 and 3835 mAh cm-3, with dendrite-free plating and stripping reported in suitable electrolytes.Mg is also described as abundant and safer to handle than Li, supporting potential cost-effective and eco-friendly processes.
  • Motivation, principle and historical development: Finding chemically stable electrolyte–cathode–anode combinations remains a major technical challenge for rechargeable magnesium batteries.Electrolyte stability toward transition-metal oxide or sulfide cathodes was poor in early systems.
  • Motivation, principle and historical development: More than 2,000 charge–discharge cycles at 100% depth of discharge with less than 15% capacity deterioration were demonstrated using MgxMo3S4 and a THF/Mg(AlCl2BuEt)2 electrolyte.The initial capacity of these systems was 60-90 mAh g-1 at 0.1–1 mA cm-2.
  • Cathode materials: Divalent Mg2+ is difficult to intercalate into many electrode hosts, making cathode kinetics, reversibility, Coulombic efficiency, capacity, and voltage key development targets.Conversion cathodes can reach ca. 820 mAh g-1 but are not stable toward high-capacity operation.
  • Electrolytes for Mg batteries: DCC electrolytes demonstrated high-voltage stability up to 2.5 V, excellent reversibility over several thousand cycles, and faster Mg2+ intercalation kinetics in Chevrel-type cathodes.Reported DCC properties were nevertheless contradictory, raising concerns about synthesis reproducibility.
  • Cathode materials: MgxMo6S6Se2 delivered 110-100 mAh g-1 at 1.1-1.3 V after 100 cycles with a DCC electrolyte and Mg anode.Faster Mg2+ intercalation kinetics and ionic mobility can come at the cost of capacity.

2.2.2. Ca-ion batteries: State-of-the-art

Ca-ion batteries offer promising capacities and voltage, but development remains constrained by passivation, electrolyte, and slow-divalent-ion transport challenges.

  • Anodes: Calcium anodes offer volumetric and gravimetric capacities of 2072 mAh cm−3 and 1337 mAh g−1, exceeding graphitic Li-ion anodes.The corresponding graphite values are 300–430 mAh cm−3 and 372 mAh g−1.
  • Anodes: Passivation layers including Ca(OH)2, CaCO3, calcium alkoxides, and CaF2 hinder calcium deposition and battery performance.Reversible deposition was initially demonstrated only at elevated temperatures near 100 °C.
  • Remaining challenges: Despite recent progress, Ca batteries face low diffusion rates, passivation, and the need for suitable cathodes, electrolytes, and efficient cation hosts.The review characterizes the field as being at an initial stage and unlikely to advance without creative approaches.
  • Electrolytes and deposition: The first reversible calcium electrodeposition system used 0.45 M Ca(BF4)2 and cycled for 30 cycles at 50–100 °C, with no room-temperature activity.This result enabled further electrolyte and cathode optimization.
  • Electrolytes and deposition: Ca(BH4)2 in THF enabled room-temperature plating and stripping with 1 mAh cm−2 at 1 mA cm−2, low polarization near 100 mV, and more than 50 cycles.A small amount of CaH2 formed through reaction between deposited calcium and the electrolyte.
  • Full cells: Ca-ion full cells reached 4.45–4.6 V with 94–95% capacity retention after 300–350 cycles using graphite-based or dual-intercalation chemistries.Reported capacities included 66 mAh g−1 at 2 C and 62 mAh g−1 final discharge capacity.
  • Electrolytes and future directions: A new Ca electrolyte reversibly plated and stripped calcium at room temperature, with oxidative stability up to 4.5 V and ionic conductivity above 8 mS cm−1.The electrolyte was reported as synthesizable in various solvents and compatible with multiple host materials.

2.2.3. Overview of Zn batteries

Aqueous Zn-ion batteries are attractive for low-cost, safer storage, while their mechanisms and cathode behavior remain complex. Vanadium-based systems show strong capacity and cycling results, including long-lived porous hydrated structures.

  • Aqueous Zn-ion batteries: Aqueous Zn-ion batteries use Zn anodes with manganese-, vanadium-, Prussian-blue-, or polyanion-based cathodes in slightly acidic media.Zn2+ insertion and extraction can occur in tunnel-type and layered host structures.
  • Aqueous Zn-ion batteries: Zn-MnO2 batteries have suffered from Zn dendrite formation and irreversible discharge capacities.These issues motivate continued mechanistic studies and alternative cathode development.
  • Vanadium cathodes: Vanadium-based cathodes can approach 400 mAh g−1 and offer greater stability and multiple oxidation states than Mn-based cathodes.Their varied V–O polyhedral frameworks support potential reversible Zn2+ deintercalation.
  • Vanadium cathodes: Water-containing Zn0.25V2O5·nH2O enables highly reversible exchange of 1.1 Zn2+ to form Zn1.35V2O5·nH2O.Water expands the structure and appears to facilitate Zn2+ intercalation, although the mechanism can involve multiple steps.
  • Applications: Aqueous ZIBs combine relatively high ionic conductivity of approximately 1 S cm−1 with potential applicability to grid-scale energy storage.The review also identifies safety and low-cost materials as relevant advantages for this application.

2.2.4. Al batteries: Electrolyte challenges

Al-ion batteries have demonstrated high voltage, rapid operation, and long cycling, but electrolyte cost, acidity, corrosion, and low energy density constrain their development.

  • Ionic-liquid systems: Al-ion batteries have used Al metal with pyrolytic graphite, carbon, V2O5 nanowires, or graphitic foam in ionic-liquid electrolytes.The first Al-ion rechargeable battery was demonstrated in 2011 using V2O5 nanowires and an Al-metal anode.
  • Remaining challenges: Al-ion batteries remain at an early development stage because large Al3+ cations are difficult to intercalate, restricting application domains and increasing initial cost.The review specifically identifies low energy density as an additional limitation.
  • Ionic-liquid systems: A graphite-based Al-ion cell showed a 0.55 V Al3+ intercalation plateau, decreasing capacity from 305 mAh g−1 initially to 273 mAh g−1 after 20 cycles.A fluorinated natural graphite nanosheet cell delivered approximately 300 mAh g−1 but only 75% Coulombic efficiency over 40 cycles.
  • Ionic-liquid systems: A 3D graphitic-foam Al-ion battery exhibited discharge plateaus near 2 V and cycling up to 7500 cycles at ultrahigh current densities.Ionic-liquid electrolytes provide beneficial performance but remain expensive.
  • Electrolyte challenges: Aqueous Al batteries require highly concentrated Al salt to obtain high energy density, increasing acidity and corrosion of the Zn negative electrode.Al3+ hydrolysis makes the electrolyte aggressive toward zinc.

3. Anionic shuttles

Anionic-shuttle batteries use fluoride or chloride ions as charge carriers, offering high theoretical energy densities but facing conductivity, reversibility, solubility, and temperature constraints.

  • F-ion batteries: Fluoride-ion batteries shuttle F− between metal electrodes, with electrode reactions involving reversible metal fluoride formation and reduction.The concept offers theoretical voltages of 1–3 V and potentially high energy densities from multivalent metals and dense metal fluorides.
  • F-ion batteries: Early solid-state F-ion cells used a tysonite electrolyte but required 160 °C operation because room-temperature conductivity was only 10^-7 S cm−1.The electrolyte layer was 600 µm thick for mechanical stability.
  • F-ion batteries: Ternary fluoride electrolytes such as BaSnF4 and BiSnF4 enabled a reversibly operating F-ion battery at room temperature with conductivities around 10^-1 S cm−1.The Sn/BaSnF4/BiF3 cell showed redox peaks at 0.1 V and 0.58 V at 25 °C.
  • F-ion batteries: The room-temperature F-ion cell delivered 120 mAh g−1 initially at 10 μA cm−2, below BiF3’s theoretical 302 mAh g−1 because conversion was incomplete.Cycling performance was demonstrated from room temperature to 150 °C.
  • F-ion batteries: Liquid-electrolyte F-ion secondary batteries remain unconvincing because proton attraction can form HF and cells fade rapidly after a few cycles.These issues limit reversibility in general.
  • Cl-ion batteries: Cl-ion batteries replace F− with Cl− and can use abundant metals, but chloride solubility limits electrode choices such as FeCl3.Proposed solutions include low-solubility chloride hosts, oxychlorides, and solid electrolytes with higher Cl− conductivity.

4. MH-based Batteries

MH-based batteries use reversible hydrogen storage in alkaline NiMH systems and related Li-ion configurations. Advances in alloy composition and structure improve capacity, activation, reversibility, and practical deployment, while delithiation kinetics remain challenging for some MH-LIB anodes.

  • NiMH batteries: NiMH batteries operate in concentrated KOH through coupled Ni(OH)2/NiOOH cathode and M/MHx metal-hydride anode reactions.The discharge reactions are given for the cathode and anode, with standard potentials of +0.49 V and −0.83 V, respectively.
  • NiMH batteries: Ternary Mg-containing intergrowth alloys reduce amorphization and consolidate multi-plateau pressure behavior into a single practical pressure plateau.Magnesium substitution occurs in [R2T4] sub-units; the resulting materials have reduced molar mass and improved weight capacity.
  • NiMH batteries: Up to about 400 mAh g-1 weight capacity is obtained for Mg-containing intergrowth-phase anodes.Further optimization can raise electrochemical capacity to 420 mAh g-1 through stoichiometry, composition, rare-earth selection, nanostructuring, mechanistic study, and modelling.
  • NiMH batteries: La1.5Nd0.5MgNi9 and La2MgNi9 alloys show superior discharge performance to commercial AB5 alloys, while La substitution improves characteristics through faster hydrogen diffusion.A secondary LaNi intermetallic comprising 3% of the alloy catalyzes hydrogenation of the main 97% Laves-type intermetallic and facilitates activation.
  • MH-accommodated Li-ion batteries: MH-LIB studies show straightforward lithiation but difficult or incomplete delithiation, reflecting kinetic limitations despite increased film conductivity after Mg formation.One film doubled in thickness during the first cycle while only 25% delithiation was achieved; metallic Mg increased conductivity.
  • MH-accommodated Li-ion batteries: Combining MgH2 and TiH2 can produce composition-dependent reversibility, with cooperative interfaces improving TiH2 conversion reversibility and reducing polarization.Good reversibility and lower polarization are associated with a Mg/Li matrix, modified interfaces, and better accommodation of volume changes.

5. Discussion and major challenges ahead

Post-Li-ion systems show rapid progress across Na-, Mg-, Ca-, Zn-, Al-, anionic-, and MH-based batteries, but performance remains constrained by materials compatibility, electrolyte stability, energy density, and cycling. The review emphasizes cell-level integration, standardized comparisons, and safer electrolyte strategies.

  • Discussion and major challenges ahead: Na-ion cathodes and anodes can approach classical Li-ion battery performance, but similar-electrode Na-ion systems remain lower in energy density for electric vehicles.Further gains require higher operating voltages, insertion of more than one Na ion per formula unit, and electrolytes with wider electrochemical windows.
  • Discussion and major challenges ahead: Na-ion research has expanded rapidly, including cells demonstrating more than 150 mAh g-1 capacity and an ionic-liquid Al-ion cell stable for 7500 cycles at 2 V.Successful aqueous Al-ion electrolytes have also been reported, although cathode development at the cell level requires further work.
  • Discussion and major challenges ahead: Mg batteries require compatible electrode–electrolyte chemistries that safely conduct and intercalate Mg2+ with acceptable cyclability.Electrolytes commonly have low electrochemical stability, halides and fluorides can be corrosive, aluminate species are moisture- and air-sensitive, and complex organic syntheses can be difficult to reproduce.
  • Discussion and major challenges ahead: Mg electrode optimization involves a trade-off: intercalation cathodes are more stable at higher voltages but have low capacities, whereas conversion cathodes offer high-energy potential at modest stability.Passivation layers block Mg2+ diffusion, while dendritic magnesium deposition has also been observed during electrodeposition.
  • Discussion and major challenges ahead: Comparing post-Li-ion technologies is difficult because reported performance depends on the complete cell combination and inconsistent testing conditions.Pseudo-reference electrodes can produce potential shifts and unstable behavior, motivating consistent protocols for half-cell measurements.
  • Discussion and major challenges ahead: Ca-ion batteries are limited by slow polyvalent-cation diffusion, working voltages below 2.0 V, and cycling stability within 100 cycles.Hydrated compounds can shield Coulombic interactions, while replacing metallic calcium with intercalation-type anodes can avoid calcium plating and stripping.
  • Discussion and major challenges ahead: Hybrid and aqueous systems offer application-specific opportunities, including Zn-based or Al-based aqueous batteries for quasi-stationary storage and flexible Zn hybrid cells.Zn/PHE/LMO and Zn/PHE/LFP hybrid cells reach 1.8 V and 1.18 V versus Zn2+/Zn, respectively, under the reported configuration.

6. Summary

Beyond-Li-ion batteries are being developed to meet expanding mobile, transport, and storage needs through diverse multivalent, aqueous, solid-state, and MH-based systems. Their success depends on accurate comparison, cell integration, electrode optimization, durability, and safer electrolyte choices.

  • Summary: The review compares beyond-Li-ion systems using energy density relative to LIBs and durability, considering both electrodes and full-cell units.Fig. 12 provides an overview, while some high-current-rate data may affect full-cell specific energy.
  • Summary: Na-ion batteries are approaching commercial Li-ion performance in energy density, while continued development is expected to reduce their prices relative to LIBs.The cited conclusion qualifies this technology as still under development by academic and start-up companies.
  • Summary: Beyond-Li-ion performance requires careful electrode optimization and cell design so material advantages can translate into systems that surpass state-of-the-art LIBs.The review stresses that suitable post-Li-ion batteries depend on integrating electrodes into an appropriate cell configuration and assembly.
  • Summary: Solid-state or gel electrolytes are expected to receive substantial attention because they offer safer operation, higher energy density, and long stability in stacked cells.The review also identifies aqueous Zn and Al systems with long-term cyclability as candidates for quasi-stationary energy storage.
  • Summary: NiMH batteries continue serving rechargeable sectors and are being further integrated into electric vehicles and railways, while MH-LIBs show potential as solid-state Li/Na batteries.MH-LIB configurations are associated with high energy density and safety in the review’s supported scope.
  • Summary: Future assessments should report end-of-life energy density, interface stability, aging, degradation mechanisms, and long-term operation across varied conditions.The review also calls for detailed study of recycling-related treatment and remedies to support better-performing batteries and lower recycling costs.

Graphical Abstract

The review compares post-Li-ion and hydride-based battery prototypes across energy density, stability, safety, cost, and operating conditions. The comparison highlights application-specific trade-offs, including promising aqueous systems and persistent electrolyte, capacity, voltage, and cycling limitations.

  • Beyond Li-ion technologies are considered necessary to match battery systems to diverse applications emerging during the energy transition.
  • The comparison covers Na-ion, Mg, Ca-ion, Zn-ion, Al-ion, anionic-shuttle, NiMH, and hydride-accommodated Li-ion batteries.
  • Na-based prototypes offer abundance, lower large-scale cost, and better safety, but generally provide moderate energy density.
  • Mg and Ca systems retain abundance and low-cost advantages, while reported examples show low capacity or energy density relative to higher-energy alternatives.
  • Zn-based aqueous prototypes combine 70-75 Wh kg-1 energy density with safety, low cost, facile manufacturing, and wide-temperature operation.
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