Polymer Electrolytes For Lithium Metal Batteries Research Articles

An environmentally friendly and scalable manufacturing route to the high performance composite polymer electrolytes for lithium-metal batteries

Environmentally friendly manufacturing of flexible all-solid-state electrolytes in large-scale and low cost is important for market entering of lithium metal batteries. Herein, a simple and practical solvent-free route to the high performance composite polymer electrolyte is proposed by infiltrating the hot-molten polyether polymer (F127)/Li-salt (LiTFSI) slurry into a thin cellulose fibrous membrane. The good compatibility between the slurry and cellulose membrane allows the formation of a highly dense F127/LiTFSI/cellulose composite electrolyte with a thin thickness of 28 μm. The solvent-free feature without side-reaction as well as the good mechanical stability of such electrolyte makes great significance to ensure the safety and stability of the batteries. Therefore, its Li symmetric cell can stably operate with an ultralong lifespan of more than 3600 h without dendritic growth of metal lithium, and the LiFePO4//Li cell can also deliver an excellent cycling stability with an initial capacity of 130.1 mAh g−1 and a capacity retention of 84.11 % after more than 260 cycles at 0.5C and 60 °C. Additionally, the performance of high-loading cathode full cell and the flexible pouch cell further confirm its excellent stability and safety for practical use.

Coconstruction of Supramolecular Lithium-Conducting Cross-Linked Networks Based on PVDF and Triblock Polymer Nanomicrosphere Solid-State Polymer Electrolytes for Lithium-Metal Batteries.

Uneven lithium plating and low ionic conductivity currently impede the realization of high-capacity rechargeable lithium metal batteries. And the conventional poly(ethylene oxide) (PEO) solid-state electrolytes are unsuitable for high-energy-density Li anode applications due to their low lithium-ion transference number and high reactivity with Li metal, leading to detrimental dendrite formation and potentially hazardous exothermic reactions with the electrolyte. In this study, we employ a supramolecular approach to develop a novel polymer solid-state electrolyte based on poly(vinylidene fluoride) (PVDF) and a novel triblock polymer nanomicrosphere, (poly(ε-caprolactone)-poly(ethylene glycol)-poly(ε-caprolactone), (PCL-PEG-PCL). The abundance of carbonyl and ether-oxygen functional groups in PCL-PEG-PCL enhances the lithium coordination environment within the polymer solid-state electrolyte. Additionally, the original C-F moieties of PVDF form hydrogen bonds with C-H and terminal hydroxyl groups in PCL-PEG-PCL, collectively creating a multichannel fast Li+-conducting supramolecular cross-linked network. The resulting electrolyte demonstrates a high ionic conductivity of 1.4 × 10-3 S cm-1 and an extended electrochemical window of 5.2 V. Moreover, the electrolyte exhibits a high lithium-ion transference number (tLi+ = 0.63) at room temperature and exhibits excellent interfacial compatibility with the lithium metal anode. For the resulting electrolyte utilized in LiFePO4 batteries, the capacity retention of the cells assembled with this electrolyte exceeds 91.3% after 1000 cycles at 25 °C and 2 C (0.281 mA cm-2).

Perfluorinated Single-Ion Li+ Conducting Polymer Electrolyte for Lithium-Metal Batteries

Single-ion (Li+) conducting electrolytes with a high Li+ conductivity and transference number (LTN) are promising electrolyte candidates for eliminating the concentration polarization and inhibiting the growth of lithium dendrites in lithium-metal batteries at high power and energy densities. This study presents the synthesis and electrochemical characterization of an AB-type single-ion Li+ conducting polymer consisting of a perfluorinated lithium-salt monomer (A) covalently bonded to a polyethylene glycol monomer (B). An investigation into several plasticizers reveals that ether-based solvents with moderate dielectric constants significantly enhance the Li+ conductivity of single-ion (Li+) conducting gel polymer electrolytes (SIC-GPE) while also maintaining the mechanical integrity of SIC-GPE. The perfluorinated lithium-salt units with weakly coordinating anions provide the advantage of high Li+ conductivity (1.1 × 10–4 S cm–2) and transference number (0.92), while polyethylene glycol units contribute to high flexibility and enhance plasticizer wettability in the SIC-GPE. The interfacial stability and electrochemical performance of SIC-GPE are demonstrated in lithium-metal symmetric cells (maintaining stability for >1300 h at 1 mAh cm–2) and lithium-metal batteries (retaining 98% capacity after 200 cycles).

Single-phase local-high-concentration solid polymer electrolytes for lithium-metal batteries

Single-phase local-high-concentration solid polymer electrolytes for lithium-metal batteries

Towards an in-Depth Understanding of Single-Ion Conducting Polymer Electrolytes for Lithium-Metal Batteries

Recently, we have reported a new polyarylene-based single-ion conducting multi-block copolymer electrolyte providing very high ionic conductivities of about 1 mS cm-1 at ambient temperature and excellent cycling stability of LiNMC811 (LiNi0.8Mn0.1Co0.1O2) cells – even at 0 °C.1–3 Further improvement of this new electrolyte system, however, requires an in-depth understanding of ideally each single functional unit in the polymer.Herein, we present some of our latest results on the experimental and theoretical investigation of stepwise modified copolymers in order to decipher the impact of the different functional groups on the eventual mechanical, thermal, chemical, and electrochemical behavior. This stepwise modification includes, amongst others, the replacement of the biphenyl unit by a series of bisphenol derivatives and the variation of the ionophobic and ionophilic block. The former approach provides the unique opportunity to investigate the influence of the monomer substitution pattern, while the latter unveils some rather unexpected findings concerning the impact of the lithium concentration in the electrolyte. References H.-D. Nguyen et al., Energy Environ. Sci., 11, 3298–3309 (2018).D. Steinle et al., J. Solid State Electrochem., 26, 97–102 (2022).Z. Chen et al., Nano Energy, 77, 105129 (2020).

Interfacial Stabilizing Effect of Lithium Borates and Pyrrolidinium Ionic Liquid in Gel Polymer Electrolytes for Lithium-Metal Batteries

Interfacial Stabilizing Effect of Lithium Borates and Pyrrolidinium Ionic Liquid in Gel Polymer Electrolytes for Lithium-Metal Batteries

Highly Conductive Polyoxanorbornene-Based Polymer Electrolyte for Lithium-Metal Batteries.

This present study illustrates the synthesis and preparation of polyoxanorbornene-based bottlebrush polymers with poly(ethylene oxide) (PEO) side chains by ring-opening metathesis polymerization for solid polymer electrolytes (SPE). In addition to the conductive PEO side chains, the polyoxanorbornene backbones may act as another ion conductor to further promote Li-ion movement within the SPE matrix. These results suggest that these bottlebrush polymer electrolytes provide impressively high ionic conductivity of 7.12 × 10-4 S cm-1 at room temperature and excellent electrochemical performance, including high-rate capabilities and cycling stability when paired with a Li metal anode and a LiFePO4 cathode. The new design paradigm, which has dual ionic conductive pathways, provides an unexplored avenue for inventing new SPEs and emphasizes the importance of molecular engineering to develop highly stable and conductive polymer electrolytes for lithium-metal batteries (LMB).

Development of metal-organic framework materials as solid-state polymer electrolytes for lithium-metal batteries: A Review

Metal-organic frameworks (MOFs) have broad prospects as functional nanoparticles in lithium metal batteries (LMBs) due to their long-distance arrangement, adjustable size and chemical custom channels. Many MOFs and their derivatives are being studied as substrates or filling components of electrode and electrolyte materials. The application of metal-organic framework materials in this field is expected to further improve the safety, stability, energy density and cycle performance of solid-state LMBs. The controllable synthesis and predictable physical and chemical properties facilitate structure building and exploration of the reaction mechanism of LMBs at the molecular or atomic level. The composition of the electrolyte often has a complex impact on the performance of the battery, especially in flexible solid electrolytes, so the reasonable and controllable design of the three-dimensional electrolyte network is an important topic. In this review, the applications of MOFs and their derivatives in solid-state polymer electrolytes for LMBs are summarized.

Surface positive-charged modification of inorganic fillers to optimize lithium ion conductive pathways in composite polymer electrolytes for lithium-metal batteries

The incorporation of inorganic fillers into composite polymer electrolytes (CPEs) is a common strategy to improve ionic conductivity. However, the high surface energy of inorganic fillers typically aggravates poor interfacial contact with polymer chains. Herein, we develop a surface positive-charge modification strategy for enhancing the intermolecular interaction of poly(ethylene oxide) (PEO) electrolytes with inorganic fillers and optimizing lithium ion (Li+) conductive pathways in CPEs. The SiO2 nanoparticles are coated with a polydopamine adhesive layer and then functionalized with a branched polyethyleneimine positively charged functional layer. Such surface modification not only effectively induces more amorphous structure into the PEO matrix but also promotes the dissociation of lithium salts and activates more free Li+ in the PEO to accelerate Li+ transport. The CPEs achieved a superior ionic conductivity of 6.12 × 10-5 S cm−1 at 30 °C. In addition, the modified fillers could induce the formation of a lithium fluoride (LiF)-rich solid-state interphase and correspondingly achieve excellent compatibility with Li metal. The Li symmetric battery using the as-prepared CPEs delivered stable Li plating/stripping performances over 3960 h under 0.2 mA cm−2. The resulting LiFePO4|Li battery has an excellent capacity retention of 92.8 % after 260 cycles at 0.5C and 60 °C.

Bifunctional Solid-State Copolymer Electrolyte with Stabilized Interphase for High-Performance Lithium Metal Battery in a Wide Temperature Range.

Solid-state polymer electrolytes (SPEs) are expected to guarantee safe and durable operations of lithium metal batteries (LMBs). Herein, inspired by the salutary poly(vinyl ethylene carbonate) (PVEC) component in the solid electrolyte interphase, cross-linking vinyl ethylene carbonate and ionic liquid copolymers were synthesized by in-situ polymerization to serve as polymer electrolyte for LMBs. On one hand, due to rich ester bonds of PVEC, Li+ could transfer by coupling/decoupling with oxygen atoms. On the other hand, the imidazole ring of ionic liquid could facilitate the dissociation of lithium salt to promote the free movement of Li+ . The bifunctional component synergistically increased the ionic conductivity of the SPE to 1.97×10-4 S cm-1 at 25 °C. Meanwhile, it also showed a wide electrochemical window, superior mechanical properties, outstanding non-combustibility, and excellent interfacial compatibility. The bifunctional copolymer-based LiFePO4 batteries could normally operate at 0 to 60 °C, making them a promising candidate for wide-temperature-rang LMBs.

Organic ionic plastic crystal enhanced interface compatibility of PEO-based solid polymer electrolytes for lithium-metal batteries

Polyethylene oxide (PEO)-based solid polymer electrolytes (SPEs) are appealing solid electrolytes for lithium-metal batteries (LMBs) due to their high safety, low cost and flexibility. However, PEO'snarrow electro-chemical potential window and poor interfacial compatibility with the electrode restrict PEO-based SPE development. Herein, we used a solution-casting method to prepare PEO-based SPE membranes reinforced with an organic ionic plastic crystal—N,N-diethylpyrrolidinium bis(fluorosulfonyl)amide (C2epyrFSI). The as-prepared SPE exhibits high ionic conductivity of 3.02 × 10−4 S cm−1 at 50 °C, an extremely wide electro-chemical window (5.1 V) and flexible mechanical properties. Using SPE, the Li symmetric cells can cycle for 2000 h at a current density of 0.1 mA cm−2 without short circuiting at 50 °C. Furthermore, the Li|SPE|LiFePO4 all-solid-state LMBs have a high initial discharge specific capacity of 157.3 mAh g−1 at 0.2C and a capacity retention rate of 96% after 120 cycles. This study shows that the PEO-C2epyrFSI SPE is a promising electrolyte for all-solid-state LMBs.

Reducing crystallinity in solid polymer electrolytes for lithium-metal batteries via statistical copolymerization

The discovery that polyethylene oxide promotes ionic conductivity led to the development of solid polymer electrolytes. However, their conductivity is severely reduced by crystallinity. Here, statistical copolymerization is used to design macromolecular architectures where crystallinity is disrupted by a minimal amount of non-ethylene oxide comonomer units. Using the Flory exclusion model, we demonstrate that polymers containing 18 mol% comonomer and 18 wt% LiTFSI are devoid of crystallinity. A 10 mol% comonomer content is sufficient to reach a conductivity of 0.3 × 10−4 S cm−1 at 25 °C. The Li+ transference number is 0.6, indicating that the comonomer units not only limit the crystallinity but also weaken the strength of the Li+ coordination to the polymer. The resulting solid polymer electrolyte is effective in an all-solid LFP|Li-metal battery operating at 25 °C, demonstrating that statistical copolymerization is an efficient tool for polymer electrolyte design.