Bingqian Liu and V. Sara Thoi · Chemical Communications · 2022
Describe MOF design strategies for lithium-sulfur cathodes, especially tuning polysulfide affinity, ionic conductivity, porosity, redox activity, electrode density and low-temperature behaviour.
The review’s argument is preserved as a navigable set of section summaries.
Reviews node lithiation, redox-active anthraquinone incorporation and porosity tuning as ways to improve ion conductivity, charge transfer and rate capability.
Relevance: Core · 4009 · 2.2. Promoting charge transport in MOFs
Summarises the framework design rules and highlights unresolved needs: denser polysulfide anchors, mapped ion pathways, improved electronic conductivity and balanced electrode energy density.
Relevance: Core · 4014 · 4. Conclusions
Organises the review around increasing polysulfide affinity, ionic conductivity and charge-transport efficiency through MOF tunability.
Relevance: Core · 4006 · 2. Design strategies for constructing better sulfur cathodes · Scheme 1
Frames Li-S batteries as high-energy but cyclability-limited systems where soluble polysulfides create active-material loss, passivation and impedance; introduces MOFs as tunable porous sulfur hosts.
Relevance: Core · 4005 · 1. Introduction
Uses CuBTC to show how unsaturated Lewis acidic Cu sites bind sulfur species and how particle size changes surface-site density, polysulfide retention and performance.
Relevance: Core · 4006 · 2.1.1. Coordinatively unsaturated metal sites for polysulfide binding · Fig. 1
Reviews physical encapsulation and chemical binding approaches, including open Cu sites, organic linker tethering and node-bound lithium thiophosphate groups.
Relevance: Core · 4006 · 2.1. Promoting interactions between MOFs and lithium polysulfides
Separates covalent organic-linker tethering from post-synthetic node functionalisation, using maleimide-UiO-66 and lithium thiophosphate on Zr-MOF nodes as examples.
Relevance: Core · 4007 · 2.1.2. Polysulfide tethering groups · Figs. 2-4
Extends the materials design discussion to high-density graphene/ethyl-cellulose composite electrodes and LPS-functionalised additives for low-temperature operation.
Relevance: Core · 4012 · 3. Towards practical implementation of MOF-based Li-S batteries · Figs. 8-9
Classification systems are attributed to this review and are not treated as a global material registry.
The review distinguishes pore confinement from chemical binding at Lewis acidic metal sites, organic linkers and Zr-MOF nodes.
Categories: Physical encapsulation in pores · Open metal sites · Organic linker tethering groups · Post-synthetic node functionalisation
4007 · 2.1.2. Polysulfide tethering groups
The implementation section separates electrode packing/contact problems from low-temperature transport and clustering problems.
Categories: Low electronic conductivity · Low electrode density · Low-temperature ion diffusion and polysulfide clustering · Sulfur loading and electrode porosity trade-off
4012 · 3.1. High-density cathode through materials engineering
Scheme 1 visually organises the review into chemical anchoring, transport enhancement and implementation-level electrode design.
Categories: Promote MOF-polysulfide interactions · Enhance charge transport · Achieve practical implementation
4006 · 2. Design strategies for constructing better sulfur cathodes · Scheme 1
Section 2.2 presents transport as coupled ionic and electronic limitations that can be altered by lithiation, redox chemistry and pore architecture.
Categories: Node lithiation for Li-ion pathways · Redox-active linkers for electron and ion mediation · Porosity tuning to balance ion flux and redox-site loading
4012 · 2.2.3. Porosity tuning
Review-defined families retain their representative materials and conduction descriptions.
Zr-MOFs incorporating redox-active anthraquinone either as a linker or as a post-synthetically grafted open-site component.
Conduction: AQ provides redox-active sites for electron storage/mobilisation and Li-ion interaction, while loading must be balanced against pore blockage.
Representative materials: 2,6-Zr-AQ-MOF · Li-2,6-Zr-AQ-MOF · NU-1000-AQ · MOF-808-AQ
Nodes / linkers: Zr oxide clusters · 2,6-dicarboxy-9,10-anthraquinone · Anthraquinone-2-carboxylate
4010 · 2.2.2. Redox activity incorporation · Fig. 6
Copper paddlewheel MOF whose axial aqua ligands can be removed to expose Lewis acidic Cu sites for sulfur/polysulfide binding.
Conduction: Charge transport is influenced by surface-site density and particle morphology; smaller particles provide more undercoordinated Cu sites for polysulfide retention.
Representative materials: CuBTC · CuBTC@S
Nodes / linkers: Copper paddlewheel · Benzene-1,3,5-tricarboxylate
4006 · 2.1.1. Coordinatively unsaturated metal sites · Fig. 1
Zr-MOFs bearing PS4-based lithium thiophosphate groups at Zr nodes or defect sites to tether polysulfides and promote Li-S cycling.
Conduction: Lithium thiophosphate is framed as both a polysulfide tether and an ion-conducting motif that can lower overpotential and alter low-temperature polysulfide speciation.
Representative materials: LPS-UiO-66 · LPS-MOF-808 · MOF-808-LPS
Nodes / linkers: Zr6 clusters · UiO-66 linkers · MOF-808 linkers · Node-bound thiophosphate
4008 · 2.1.2.2 Open metal site functionalization · Fig. 3
UiO-66 derivative with maleimide groups on BDC linkers for covalent reaction with sulfide/polysulfide species.
Conduction: Maleimide tethering reduces polysulfide dissolution and may reduce cell polarisation by improving sulfur redox kinetics.
Representative materials: Mi-UiO-66 · NH2-UiO-66 control
Nodes / linkers: Zr6 clusters · Maleimide-functionalised BDC · Amino-functionalised BDC
4007 · 2.1.2.1. Organic linker functionalization · Fig. 2
High-density sulfur-loaded MOF cathode composites where graphene/ethyl cellulose replaces conventional carbon black and binder mixtures.
Conduction: Improved interfacial contact and more compact coatings are used to address low MOF conductivity and low electrode density.
Representative materials: MOF-808@S/GEC · LPS-MOF-808@S/GEC · MOF-808+S/SP
Nodes / linkers: Zr6 clusters · MOF-808 linkers · Graphene/ethyl cellulose conductive composite
4012 · 3.1. High-density cathode through materials engineering · Fig. 8
Robust Zr-oxo cluster frameworks used as platforms for defect engineering, node functionalisation, lithiation and sulfur hosting.
Conduction: Native frameworks are stable and porous but typically electronically insulating; defects and open sites enable Li-ion incorporation and functional-group attachment.
Representative materials: UiO-66 · MOF-808 · NU-1000
Nodes / linkers: Hexanuclear Zr-oxo clusters · Dicarboxylate linkers · Multicarboxylate linkers · Carboxylate modulators
4005 · 1. Introduction
Review-level synthesis principles remain separate from primary-study recipes.
Combine sulfur-loaded MOF particles with graphene/ethyl cellulose to improve interfacial contact and electrode compactness.
Claimed effects: Improves gravimetric and volumetric capacity by addressing low electronic conductivity and low density of MOF-incorporated cathodes.
Controlling variables: Sulfur loading · Conductive additive identity · Slurry morphology · Electrode coating density · Interfacial contact
Representative materials: MOF-808@S/GEC · LPS-MOF-808@S/GEC
Caveat: Implementation benefit depends on electrode architecture, not just intrinsic framework chemistry.
4013 · 3.1. High-density cathode through materials engineering · Fig. 8
Use organic linker functionality, illustrated by maleimide groups, to chemically capture sulfide/polysulfide species within a MOF host.
Claimed effects: Forms C-S bonds with polysulfide species, avoids dissolution and improves cycling and rate performance relative to non-tethering controls.
Controlling variables: Linker functional group · Polysulfide reactivity · Framework stability · Cathode additive choice
Representative materials: Mi-UiO-66 · NH2-UiO-66
Caveat: The review frames this as a targeted chemical strategy rather than a universal solution for all polysulfide chemistries.
4007 · 2.1.2.1. Organic linker functionalization · Fig. 2
Introduce missing-linker defects and replace labile protons at defect sites with Li ions to raise local lithium concentration.
Claimed effects: Enhances Li-ion conductivity, reduces resistance and improves rate performance when the MOF structure remains intact.
Controlling variables: Defect modulator · HCl activation · Lithiation base · Temperature · Framework crystallinity
Representative materials: Li-UiO-66(50Benz) · UiO-66(50Benz)
Caveat: Harsher lithiation conditions can increase Li content but diminish framework integrity and crystallinity, reducing benefit.
4009 · 2.2.1. Node lithiation · Fig. 5
Replace node-bound ligands or use defect/open sites to bind PS4-based lithium thiophosphate groups inside Zr-MOFs.
Claimed effects: Tethers polysulfides, lowers electrochemical overpotentials, improves sulfur utilisation and can disrupt low-temperature polysulfide clustering.
Controlling variables: Number of open Zr sites · Defect density · LPS loading · Parent MOF porosity
Representative materials: LPS-UiO-66 · LPS-MOF-808 · MOF-808-LPS
Caveat: The review notes that internal porosity is necessary; LPS-ZrO2 controls failed within 100 cycles.
4008 · 2.1.2.2 Open metal site functionalization · Figs. 3-4
Remove ligands or exploit undercoordinated surface sites to create Lewis acidic metal centres that bind sulfur species.
Claimed effects: Increases polysulfide retention and improves capacity retention by providing chemically active host sites.
Controlling variables: Thermal activation · Particle size · Surface morphology · S:MOF ratio
Representative materials: CuBTC · CuBTC@S
Caveat: The review's evidence is mainly from one CuBTC case; smaller particle size improves surface-site density but may not generalise to all MOFs.
4006 · 2.1.1. Coordinatively unsaturated metal sites · Fig. 1
Use AQ linkers or grafted AQ species to add reversible redox sites that store and mobilise electrons and lithium ions during Li-S cycling.
Claimed effects: Improves redox electrokinetics, charge-transfer resistance and sulfur utilisation, especially at high C-rates when ion flux is limiting.
Controlling variables: AQ linker identity · AQ loading · Lithiation state · C-rate · Pore accessibility
Representative materials: 2,6-Zr-AQ-MOF · Li-2,6-Zr-AQ-MOF · NU-1000-AQ · MOF-808-AQ
Caveat: Excess AQ loading blocks pores; the review stresses balancing redox-site density and free pore volume.
4011 · 2.2.3. Porosity tuning · Fig. 7
These are the review authors’ synthesis, not newly measured results.
Anthraquinone units in Zr-MOFs are interpreted as redox-active components that facilitate sulfur redox electrokinetics and improve high-rate performance.
Evidence basis: single_reference
Caveat: Low-rate benefits are less pronounced in some lithiated AQ systems; rate regime matters.
4010 · 2.2.2. Redox activity incorporation · Fig. 6
Practical MOF-based Li-S electrodes require materials engineering to overcome low electronic conductivity and low density, not only molecular-level polysulfide anchoring.
Evidence basis: single_reference
Caveat: Composite electrode benefits depend on slurry morphology and conductive substrate choice.
4012 · 3.1. High-density cathode through materials engineering · Fig. 8
Node lithiation can improve Li-ion transport and rate capability, but higher lithium content alone is insufficient if harsh lithiation damages framework integrity.
Evidence basis: single_reference
Caveat: The beneficial balance depends on defect chemistry and preservation of the UiO-66 framework.
4010 · 2.2.1. Node lithiation · Fig. 5
Lithium thiophosphate functionalisation is interpreted as disrupting low-temperature polysulfide clustering and producing more stable diffusion coefficients.
Evidence basis: single_reference
Caveat: The low-temperature mechanism is inferred from electrochemical features and variable-temperature 7Li NMR in the cited study.
4014 · 3.2. Polysulfide tethering for low temperature batteries · Fig. 9
Lithium thiophosphate node functionalisation improves cycling through polysulfide tethering, but internal porosity remains essential for the effect.
Evidence basis: single_reference
Caveat: The review's LPS-ZrO2 comparison cautions against attributing performance only to the anchor group without the porous host.
4008 · 2.1.2.2 Open metal site functionalization · Fig. 4
Maleimide-functionalised UiO-66 demonstrates that molecular sulfide-reactive chemistry can be incorporated into MOF linkers to chemically tether polysulfides.
Evidence basis: single_reference
Caveat: The review frames the maleimide case as an example of linker chemistry rather than a complete general design rule.
4007 · 2.1.2.1. Organic linker functionalization · Fig. 2
Most MOFs have low electronic conductivity because of strong metal-oxygen bonding at the node, which limits their Li-S battery performance unless transport pathways are engineered.
Evidence basis: review_reasoning
Caveat: This is a broad MOF limitation; conductive MOF subclasses may differ.
4009 · 2.2. Promoting charge transport in MOFs
MOFs are presented as tunable sulfur hosts because their polarity, porosity, conductivity, particle morphology and functional chemistry can be adjusted to confine polysulfides and mobilise charge.
Evidence basis: multi_reference
Caveat: The review focuses on MOF cathode additives/hosts and does not claim MOFs alone solve all Li-S engineering constraints.
4005 · 1. Introduction
Open or undercoordinated metal sites in MOFs can bind polysulfides and improve retention, with CuBTC used as the review's main example.
Evidence basis: multi_reference
Caveat: The strongest evidence is for Cu-based paddlewheel sites; other node chemistries require separate verification.
4006 · 2.1.1. Coordinatively unsaturated metal sites · Fig. 1
The review identifies increasing the concentration of polysulfide anchors as a future chemical need for preventing polysulfide dissolution.
Evidence basis: review_reasoning
Caveat: Anchor density must be balanced with pore accessibility and electrode energy density.
4014 · 4. Conclusions
The review states that mapping ion-conduction pathways in MOFs is needed to promote charge mobility and increase charge-discharge rate.
Evidence basis: review_reasoning
Caveat: This is an outlook statement and not a resolved mechanistic conclusion.
4014 · 4. Conclusions
For CuBTC@S, smaller particles are interpreted as providing a higher density of undercoordinated surface Cu sites, leading to better polysulfide retention and electrochemical performance.
Evidence basis: single_reference
Caveat: Particle-size effects are coupled to morphology and surface chemistry; the review does not separate every variable.
4007 · 2.1.1. Coordinatively unsaturated metal sites · Fig. 1
Redox-active loading must be balanced against pore blocking because free pore volume is necessary for high ion flux.
Evidence basis: single_reference
Caveat: The optimisation is framework-specific; higher redox-site loading is not automatically better.
4012 · 2.2.3. Porosity tuning · Fig. 7
Li-S cyclability is limited by soluble polysulfide shuttling, which couples mass transport, active-material loss, electrode passivation and impedance.
Evidence basis: multi_reference
Caveat: This is background consensus in the review, not a new measurement by the review authors.
4005 · 1. Introduction
Every row remains visibly secondary and links to a primary dossier only where the mapping is verified.
| Material | Property | Reported value | Context and quality | Primary evidence | Review source |
|---|---|---|---|---|---|
| SecondaryLi-UiO-66(50Benz) cathodes | Maximum specific capacity | 1272 mA h g-1 versus 918 mA h g-1 for UiO-66(50Benz) | MOF+S cathodes in Li-S cycling Text · Exact Reported | No verified corpus mapping | 4010 · 2.2.1. Node lithiation · Fig. 5d |
| SecondaryLi-UiO-66(50Benz) | Room-temperature ionic conductivity | 1.20 x 10^-8 S cm-1 versus 1.98 x 10^-9 S cm-1 for UiO-66(50Benz) | Pressed pellets formed from electrolyte-infiltrated MOF powders at room temperature Text · Exact Reported | No verified corpus mapping | 4009 · 2.2.1. Node lithiation · Fig. 5c |
| SecondaryLi-2,6-Zr-AQ-MOF | Ionic conductivity | 4.8 x 10^-7 S cm-1 versus 2.4 x 10^-8 S cm-1 for pristine 2,6-Zr-AQ-MOF | Pellet EIS of lithiated framework Text · Exact Reported | No verified corpus mapping | 4010 · 2.2.2. Redox activity incorporation · Fig. 6d |
| SecondaryLPS-MOF-808@S/GEC cells | Initial specific capacity | 858 +/- 51 mA h g-1 with 79.8% capacity retention | GEC composite cathode cycled at C/2 Text · Exact Reported | No verified corpus mapping | 4013 · 3.1. High-density cathode through materials engineering · Fig. 8 |
| Secondary2xLPS-MOF-808 cells | Maximum capacity increase versus MOF-808 | 300 mA h g-1 increase for 2xLPS-MOF-808 | Comparison of 0.7x, 1x and 2x LPS-MOF-808 loading Text · Exact Reported | No verified corpus mapping | 4008 · 2.1.2.2 Open metal site functionalization · Fig. 4b |
| SecondaryLPS-UiO-66 cells | Specific capacity after 100 cycles | 835 mA h g-1 versus 560 mA h g-1 for UiO-66 cells | After 100 cycles in Li-S cells Text · Exact Reported | No verified corpus mapping | 4008 · 2.1.2.2 Open metal site functionalization · Fig. 4a |
| SecondaryLPS-UiO-66 cells | Maximum specific capacity | 1193 mA h g-1 versus 891 mA h g-1 for parent UiO-66 cells | Long-term Li-S cycling in the cited LPS-MOF study Text · Exact Reported | No verified corpus mapping | 4008 · 2.1.2.2 Open metal site functionalization · Fig. 4a |
| SecondaryMOF-808-LPS | Low-temperature discharge capacity after 20 cycles | nearly 810 mA h g-1 after 20 cycles at -10 C | C/10 cycling at -10 C; minus sign verified from rendered Fig. 9 page Text · Approximate | No verified corpus mapping | 4013 · 3.2. Polysulfide tethering for low temperature batteries · Fig. 9b |
| SecondaryNU-1000-AQ+S | Capacity after 100 cycles | 693 mA h g-1 after 100 cycles at C/2 | Long-term cycling at C/2 Text · Exact Reported | No verified corpus mapping | 4011 · 2.2.3. Porosity tuning · Fig. 7d |
| SecondaryUiO-66-LPS | Low-temperature discharge capacity after 20 cycles | nearly 530 mA h g-1 after 20 cycles at -10 C | C/10 cycling at -10 C; minus sign verified from rendered Fig. 9 page Text · Approximate | No verified corpus mapping | 4013 · 3.2. Polysulfide tethering for low temperature batteries · Fig. 9b |
| Secondary2,6-Zr-AQ-MOF cells | High-rate specific capacity | 667 mA h g-1 at 2C | Rate capability at 2C Text · Exact Reported | No verified corpus mapping | 4010 · 2.2.2. Redox activity incorporation · Fig. 6c |
| Secondary2,6-Zr-AQ-MOF cells | Capacity after 300 cycles | 719 mA h g-1 after 300 cycles at 1C | 300 cycles at 1C Text · Exact Reported | No verified corpus mapping | 4010 · 2.2.2. Redox activity incorporation · Fig. 6c |
Open questions are presented as review-author priorities, not conclusions from the primary database.
The review calls for chemical strategies that increase polysulfide-anchor concentration to better prevent dissolution.
Proposed direction: Design higher-density anchor sites while preserving pore accessibility and active-material loading.
4014 · 4. Conclusions
Ion conduction pathways in MOFs remain insufficiently charted for rational improvement of charge mobility and rate capability.
Proposed direction: Combine electrochemical, spectroscopic and structural probes to identify Li-ion/polysulfide pathways through nodes, pores and guest species.
4014 · 4. Conclusions
Low electronic conductivity is identified as a major drawback of MOF hosts.
Proposed direction: Tune metal and linker components to improve orbital overlap, through-bond charge delocalisation and framework conductivity.
4014 · 4. Conclusions
Sulfur and redox-active component infiltration can lower porosity, so charge-transfer gains can conflict with ion-flux needs.
Proposed direction: Optimise pore volume, redox-site loading and conductive substrate selection together rather than maximising any single variable.
4014 · 4. Conclusions
MOF additives can extend cycle life but practical Li-S cells also require high sulfur loading, low electrode porosity and suitable gravimetric and volumetric energy density.
Proposed direction: Evaluate MOF cathode additives under electrode-level metrics including sulfur loading, electrode porosity, volumetric capacity and power density.
4014 · 4. Conclusions
Mappings show which printed review references have a verified counterpart in the frozen primary corpus.
| Reference | Study | Role and context | Corpus mapping |
|---|---|---|---|
| Ref. 12014 | Title unavailable | background_lis_mechanismCited in the introduction for the shuttle effect and Li-S battery limitations. | Unmapped |
| Ref. 42020 | Title unavailable | background_lis_mechanismCited as part of the introductory shuttle-effect literature. | Unmapped |
| Ref. 142018 | Title unavailable | mof_tunability_contextCited for synthetic control over MOF properties such as morphology, porosity and conductivity. | Unmapped |
| Ref. 162019 | Title unavailable | mof_tunability_context · review_contextCited for synthetic control and tailorability of MOF properties relevant to Li-S hosts. | Unmapped |
| Ref. 172018 | Title unavailable | mof_lis_contextCited among works using MOFs with different compositions and pore structures to mitigate polysulfide dissolution. | Unmapped |
| Ref. 202013 | Title unavailable | open_metal_sites · polysulfide_bindingCited as prior evidence that sulfur species bind at Lewis acidic Cu centres. | Unmapped |
| Ref. 252014 | Title unavailable | mof_hosts · open_metal_sitesCited as previous MOF-host work motivating later design strategies and as evidence for sulfur binding at Cu centres. | Unmapped |
| Ref. 322018 | Title unavailable | open_metal_sites · structure_property_link · polysulfide_bindingPrimary cited study for CuBTC@S, Cu-S binding, particle-size effects and Fig. 1 benchmarks. | Unmapped |
| Ref. 342021 | Title unavailable | linker_functionalisation · polysulfide_tetheringPrimary cited study for maleimide-functionalised UiO-66 and Fig. 2 cycling/tethering results. | Unmapped |
| Ref. 352019 | Title unavailable | solid_electrolyte_context · lithium_thiophosphateCited to support lithium phosphorus sulfides as Li-ion conductors and solid-state electrolytes. | Unmapped |
| Ref. 362013 | Title unavailable | polysulfide_chemistry · lithium_thiophosphateCited for phosphorus sulfides chemically interacting with lithium polysulfides through S-S bond formation. | Unmapped |
| Ref. 372019 | Title unavailable | lithium_thiophosphate · polysulfide_tethering · transport_benchmarkPrimary cited study for node-bound LPS-MOFs, their structural characterisation and cycling benchmarks in Figs. 3-4. | Unmapped |
| Ref. 392018 | Title unavailable | node_lithiation · ionic_conductivity · transport_benchmarkPrimary cited study for lithiated UiO-66, EIS-derived ionic conductivity and high-rate cycling in Fig. 5. | Unmapped |
| Ref. 412019 | Title unavailable | redox_active_mof · anthraquinone · transport_benchmarkPrimary cited study for AQ-linker Zr-MOFs and redox/transport benchmarks in Fig. 6. | Unmapped |
| Ref. 422019 | Title unavailable | porosity_context · ion_diffusionCited as prior evidence that ion diffusion can be rate-limiting and larger pores can favour charge-transfer efficiency. | Unmapped |
| Ref. 432020 | Title unavailable | porosity_tuning · anthraquinone · transport_benchmarkPrimary cited study for post-synthetic AQ loading and the loading/porosity trade-off in Fig. 7. | Unmapped |
| Ref. 442020 | Title unavailable | electrode_engineering · volumetric_capacity · transport_benchmarkPrimary cited study for high-density graphene/ethyl-cellulose MOF cathodes and Fig. 8 performance. | Unmapped |
| Ref. 472021 | Title unavailable | low_temperature · lithium_thiophosphate · polysulfide_clustering · transport_benchmarkPrimary cited study for LPS-functionalised MOFs used as low-temperature Li-S cathode additives in Fig. 9. | Unmapped |