One-Step In Situ Polymerization: A Facile Design Strategy for Block Copolymer Electrolytes

To optimize the rapid transport of lithium ions (Li⁺) inside lithium metal batteries (LMBs), block copolymer electrolytes (BCPEs) have been fabricated in situ in LMBs via a one-step method combining reversible addition-fragmentation chain transfer (RAFT) polymerization and carboxylic acid-catalyzed ring-opening polymerization (ROP). The BCPEs balanced the Li⁺ coordination characteristics of the polyether- and polyester-based electrolytes to achieve a rapid Li⁺ migration in the SPEs. The carboxylic acid played a dual role since it both catalyzed the ROP and stabilized the interface. Furthermore, the in situ assembly of LMBs did effectively enable an efficient intercalation/de-intercalation of Li⁺ at the electrode/electrolyte interface. The in situ assembled Li/BCPE4/LFP exhibited high-capacity retention of 92 % after 400 cycles at 1 C. The one-step in situ fabrication of BCPEs provides a new direction for the design of polymer electrolytes.     

Influencing Factors on Li-ion Conductivity and Interfacial Stability of Solid Polymer Electrolytes,Exampled by Polycarbonates,Polyoxalates and Polymalonates

The application of solid polymer electrolytes (SPEs) in all-solid-state(ASS) batteries is hindered by lower Li⁺-conductivity and narrower electrochemical window. Here, three families of ester-based F-modified SPEs of poly-carbonate (PCE), poly-oxalate (POE) and poly-malonate (PME) were investigated. The Li⁺-conductivity of these SPEs prepared from pentanediol are all higher than the counterparts made of butanediol, owing to the enhanced asymmetry and flexibility. Because of stronger chelating coordination with Li⁺, the Li⁺-conductivity of PME and POE is around 10 and 5 times of PCE. The trifluoroacetyl-units are observed more effective than −O−CH₂−CF₂−CF₂−CH₂−O− during the in situ passivation of Li-metal. Using trifluoroacetyl terminated POE and PCE as SPE, the interfaces with Li-metal and high-voltage-cathode are stabilized simultaneously, endowing stable cycling of ASS Li/LiNi_0.6Co_0.2Mn_0.2O₂ (NCM622) cells. Owing to an enol isomerization of malonate, the cycling stability of Li/PME/NCM622 is deteriorated, which is recovered with the introduce of dimethyl-group in malonate and the suppression of enol isomerization. The coordinating capability with Li⁺, molecular asymmetry and existing modes of elemental F, are all critical for the molecular design of SPEs.     

Covalent Organic Framework with Multi-Cationic Molecular Chains for Gate Mechanism Controlled Superionic Conduction in All-Solid-State Batteries

Although solid-state batteries (SSBs) are high potential in achieving better safety and higher energy density, current solid-state electrolytes (SSEs) cannot fully satisfy the complicated requirements of SSBs. Herein, a covalent organic framework (COF) with multi-cationic molecular chains (COF-MCMC) was developed as an efficient SSE. The MCMCs chemically anchored on COF channels were generated by nano-confined copolymerization of cationic ionic liquid monomers, which can function as Li⁺ selective gates. The coulombic interaction between MCMCs and anions leads to easier dissociation of Li⁺ from coordinated states, and thus Li⁺ transport is accelerated. While the movement of anions is restrained due to the charge interaction, resulting in a high Li⁺ conductivity of 4.9×10⁻⁴ S cm⁻¹ and Li⁺ transference number of 0.71 at 30 °C. The SSBs with COF-MCMC demonstrate an excellent specific energy density of 403.4 Wh kg⁻¹ with high cathode loading and limited Li metal source.     

In Situ Polymerized 1,3-Dioxolane Electrolyte for Integrated Solid-State Lithium Batteries

Solid-state lithium batteries are promising and safe energy storage devices for mobile electronics and electric vehicles. In this work, we report a facile in situ polymerization of 1,3-dioxolane electrolytes to fabricate integrated solid-state lithium batteries. The in situ polymerization and formation of solid-state dioxolane electrolytes on interconnected carbon nanotubes (CNTs) and active materials is the key to realizing a high-performance battery with excellent interfacial contact among CNTs, active materials and electrolytes. Therefore, the electrodes could be tightly integrated into batteries through the CNTs and electrolyte. Electrons/ions enable full access to active materials in the whole electrode. Electrodes with a low resistance of 4.5 Ω □⁻¹ and high lithium-ion diffusion efficiency of 2.5×10⁻¹¹ cm² s⁻¹ can significantly improve the electrochemical kinetics. Subsequently, the batteries demonstrated high energy density, amazing charge/discharge rate and long cycle life.     

Bimetallic Anionic Organic Frameworks with Solid-State Cation Conduction for Charge Storage Applications

A new phosphonate-based anionic bimetallic organic framework, with the general formula of A₄−Zn−DOBDP (wherein A is Li⁺ or Na⁺, and DOBDP⁶⁻ is the 2,5-dioxido-1,4-benzenediphosphate ligand) is prepared and characterized for energy storage applications. With four alkali cations per formula unit, the A₄−Zn−DOBDP MOF is found to be the first example of non-solvated cation conducting MOF with measured conductivities of 5.4×10⁻⁸ S cm⁻¹ and 3.4×10⁻⁸ S cm⁻¹ for Li₄- and Na₄- phases, indicating phase and composition effects of Li⁺ and Na⁺ shuttling through the channels. Three orders of magnitude increase in ionic conductivity is further attained upon solvation with propylene carbonate, placing this system among the best MOF ionic conductors at room temperature. As positive electrode material, Li₄−Zn−DOBDP delivers a specific capacity of 140 mAh g⁻¹ at a high average discharge potential of 3.2 V (vs. Li⁺/Li) with 90 % of capacity retention over 100 cycles. The significance of this research extends from the development of a new family of electroactive phosphonate-based MOFs with inherent ionic conductivity and reversible cation storage, to providing elementary insights into the development of highly sought yet still evasive MOFs with mixed-ion and electron conduction for energy storage applications.     

Anion-tethered Single Lithium-ion Conducting Polyelectrolytes through UV-induced Free Radical Polymerization for Improved Morphological Stability of Lithium Metal Anodes

Single Li⁺ ion conducting polyelectrolytes (SICs), which feature covalently tethered counter-anions along their backbone, have the potential to mitigate dendrite formation by reducing concentration polarization and preventing salt depletion. However, due to their low ionic conductivity and complicated synthetic procedure, the successful validation of these claimed advantages in lithium metal (Li⁰) anode batteries remains limited. In this study, we fabricated a SIC electrolyte using a single-step UV polymerization approach. The resulting electrolyte exhibited a high Li⁺ transference number (t₊) of 0.85 and demonstrated good Li⁺ conductivity (6.3×10⁻⁵ S/cm at room temperature), which is comparable to that of a benchmark dual ion conductor (DIC, 9.1×10⁻⁵ S/cm). Benefitting from the high transference number of SIC, it displayed a three-fold higher critical current density (2.4 mA/cm²) compared to DIC (0.8 mA/cm²) by successfully suppressing concentration polarization-induced short-circuiting. Additionally, the t₊ significantly influenced the deposition behavior of Li⁰, with SIC yielding a uniform, compact, and mosaic-like morphology, while the low t₊ DIC resulted in a porous morphology with Li⁰ whiskers. Using the SIC electrolyte, Li⁰||LiFePO₄ cells exhibited stable operation for 4500 cycles with 70.5 % capacity retention at 22 °C.     

Stabilizing Solid-state Lithium Metal Batteries through In Situ Generated Janus-heterarchical LiF-rich SEI in Ionic Liquid Confined 3D MOF/Polymer Membranes

Pursuing high power density lithium metal battery with high safety is essential for developing next-generation energy-storage devices, but uncontrollable electrolyte degradation and the consequence formed unstable solid-electrolyte interface (SEI) make the task really challenging. Herein, an ionic liquid (IL) confined MOF/Polymer 3D-porous membrane was constructed for boosting in situ electrochemical transformations of Janus-heterarchical LiF/Li₃N-rich SEI films on the nanofibers. Such a 3D-Janus SEI-incorporated into the separator offers fast Li⁺ transport routes, showing superior room-temperature ionic conductivity of 8.17×10⁻⁴ S cm⁻¹ and Li⁺ transfer number of 0.82. The cryo-TEM was employed to visually monitor the in situ formed LiF and Li₃N nanocrystals in SEI and the deposition of Li dendrites, which is greatly benefit to the theoretical simulation and kinetic analysis of the structural evolution during the battery charge and discharge process. In particular, this membrane with high thermal stability and mechanical strength used in solid-state Li||LiFePO₄ and Li||NCM-811 full cells and even in pouch cells showed enhanced rate-performance and ultra-long life spans.     

Advanced Lithium Extraction Membranes Derived from Tagged-Modification of Polyamide Networks

Efficient Mg²⁺/Li⁺ separation is crucial to combating the lithium shortage worldwide, yet current nanofiltration membranes suffer from low efficacy and/or poor scalability, because desirable properties of membranes are entangled and there is a trade-off. This work reports a “tagged-modification” approach to tackle the challenge. A mixture of 3-bromo-trimethylpropan-1-aminium bromide (E₁) and 3-aminopropyltrimethylazanium (E₂) was designed to modify polyethylenimine – trimesoyl chloride (PEI-TMC) membranes. E₁ and E₂ reacted with the PEI and TMC, respectively, and thus, the membrane properties (hydrophilicity, pore sizes, charge) were untangled and intensified simultaneously. The permeance (34.3 L m⁻² h⁻¹ bar⁻¹) and Mg²⁺/Li⁺ selectivity (23.2) of the modified membranes are about 4 times and 2 times higher than the pristine membrane, and they remain stable in a 30-days test. The permeance is the highest among all analogous nanofiltration membranes. The tagged-modification method enables the preparation of large-area membranes and modules that produce high-purity lithium carbonate (Li₂CO₃) from simulated brine.     

Real-time mid-IR monitoring of metathesis reactions by fiber optic FTIR spectroscopy

The real-time monitoring of metathesis reactions using a recently developed fiber optic transmission FTIR technique is reported in this paper. The ring-opening metathesis polymerization (ROMP) of 1,5-cyclooctadiene, the ring-closing metathesis (RCM) of 1,7-octadiene and the polymerization of phenylacetylene were investigated. The Schrock carbyne complex, Cl₃(dme)WCCMe₃, was used as the catalyst for these reactions. The phenylacetylene polymerization was also studied with WCl₆ as the catalyst. In the ROMP of 1,5-cyclooctadiene, monomer consumption was followed by monitoring the disappearance of the 1486 cm⁻¹ absorbance, characteristic of the CH₂ deformation vibration (δ_s CH₂) in the monomer. In the RCM of 1,7-octadiene, conversion data was obtained by monitoring the 1832 cm⁻¹ signal, which is an overtone of the wagging absorbance at 910 cm⁻¹ of the CH₂ end group in the monomer. Phenylacetylene polymerization was monitored by the disappearance of the ν -CCH stretch signal at 2110 cm⁻¹. Polymerization was much faster with the Schrock catalyst than with WCl₆, but similar conversions were reached in both reactions. Conversion data obtained by the IR technique agreed well with gravimetric product yields.     

A Highly Efficient All-Solid-State Lithium/Electrolyte Interface Induced by an Energetic Reaction

The energetic chemical reaction between Zn(NO₃)₂ and Li is used to create a solid-state interface between Li metal and Li_6.4La₃Zr_1.4Ta_0.6O₁₂ (LLZTO) electrolyte. This interlayer, composed of Zn, ZnLi_x alloy, Li₃N, Li₂O, and other species, possesses strong affinities with both Li metal and LLZTO and affords highly efficient conductive pathways for Li⁺ transport through the interface. The unique structure and properties of the interlayer lead to Li metal anodes with longer cycle life, higher efficiency, and better safety compared to the current best Li metal electrodes operating in liquid electrolytes while retaining comparable capacity, rate, and overpotential. All-solid-state Li||Li cells can operate at very demanding current–capacity conditions of 4 mA cm⁻²–8 mAh cm⁻². Thousands of hours of continuous cycling are achieved at Coulombic efficiency >99.5 % without dendrite formation or side reactions with the electrolyte.     

The Universal Super Cation-Conductivity in Multiple-cation Mixed Chloride Solid-State Electrolytes

As exciting candidates for next-generation energy storage, all-solid-state lithium batteries (ASSLBs) are highly dependent on advanced solid-state electrolytes (SSEs). Here, using cost-effective LaCl₃ and CeCl₃ lattice (UCl₃-type structure) as the host and further combined with a multiple-cation mixed strategy, we report a series of UCl₃-type SSEs with high room-temperature ionic conductivities over 10⁻³ S cm⁻¹ and good compatibility with high-voltage oxide cathodes. The intrinsic large-size hexagonal one-dimensional channels and highly disordered amorphous phase induced by multi-metal cation species are believed to trigger fast multiple ionic conductions of Li⁺, Na⁺, K⁺, Cu⁺, and Ag⁺. The UCl₃-type SSEs enable a stable prototype ASSLB capable of over 3000 cycles and high reversibility at −30 °C. Further exploration of the brand-new multiple-cation mixed chlorides is likely to lead to the development of advanced halide SSEs suitable for ASSLBs with high energy density.     

Polymers with Intrinsic Microporosity as Solid Ion Conductors for Solid-State Lithium Batteries

Solid-state electrolytes (SSEs) with high ionic conductivity and superior stability are considered to be a key technology for the safe operation of solid-state lithium batteries. However, current SSEs are incapable of meeting the requirements for practical solid-state lithium batteries. Here we report a general strategy for achieving high-performance SSEs by engineering polymers of intrinsic microporosity (PIMs). Taking advantage of the interconnected ion pathways generated from the ionizable groups, high ionic conductivity (1.06×10⁻³ S cm⁻¹ at 25 °C) is achieved for the PIMs-based SSEs. The mechanically strong (50.0 MPa) and non-flammable SSEs combine the two superiorities of outstanding Li⁺ conductivity and electrochemical stability, which can restrain the dendrite growth and prevent Li symmetric batteries from short-circuiting even after more than 2200 h cycling. Benefiting from the rational design of SSEs, PIMs-based SSEs Li-metal batteries can achieve good cycling performance and superior feasibility in a series of withstand abuse tests including bending, cutting, and penetration. Moreover, the PIMs-based SSEs endow high specific capacity (11307 mAh g⁻¹) and long-term discharge/charge stability (247 cycles) for solid-state Li−O₂ batteries. The PIMs-based SSEs present a powerful strategy for enabling safe operation of high-energy solid-state batteries.     

In-Situ Constructing A Heterogeneous Layer on Lithium Metal Anodes for Dendrite-Free Lithium Deposition and High Li-ion Flux

Constructing efficient artificial solid electrolyte interface (SEI) film is extremely vital for the practical application of lithium metal batteries. Herein, a dense artificial SEI film, in which lithiophilic Zn/Li_xZn_y are uniformly but nonconsecutively dispersed in the consecutive Li⁺-conductors of Li_xSiO_y, Li₂O and LiOH, is constructed via the in situ reaction of layered zinc silicate nanosheets and Li. The consecutive Li⁺-conductors can promote the desolvation process of solvated-Li⁺ and regulate the transfer of lithium ions. The nonconsecutive lithiophilic metals are polarized by the internal electric field to boost the transfer of lithium ions, and lower the nucleation barrier. Therefore, a low polarization of ≈50 mV for 750 h at 2.0 mA cm⁻² in symmetric cells, and a high capacity retention of 99.2 % in full cells with a high lithium iron phosphate areal loading of ≈13 mg cm⁻² are achieved. This work offers new sights to develop advanced alkali metal anodes for efficient energy storage.     

A Black Phosphorus–Graphite Composite Anode for Li-/Na-/K-Ion Batteries

Black phosphorus (BP) is a desirable anode material for alkali metal ion storage owing to its high electronic/ionic conductivity and theoretical capacity. In-depth understanding of the redox reactions between BP and the alkali metal ions is key to reveal the potential and limitations of BP, and thus to guide the design of BP-based composites for high-performance alkali metal ion batteries. Comparative studies of the electrochemical reactions of Li⁺, Na⁺, and K⁺ with BP were performed. Ex situ X-ray absorption near-edge spectroscopy combined with theoretical calculation reveal the lowest utilization of BP for K⁺ storage than for Na⁺ and Li⁺, which is ascribed to the highest formation energy and the lowest ion diffusion coefficient of the final potassiation product K₃P, compared with Li₃P and Na₃P. As a result, restricting the formation of K₃P by limiting the discharge voltage achieves a gravimetric capacity of 1300 mAh g⁻¹ which retains at 600 mAh g⁻¹ after 50 cycles at 0.25 A g⁻¹.     

Peculiarities of the Anionic Copolymerization of Styrene and Dienes in Non-Polar Solvents with Li+ as Counter-ion mvb

Summary: The anionic copolymerization of styrene and butadiene in hydrocarbon solvents initiated by lithium alkyls was first studied by Korotkov, who reported that the polymerization starts slowly and initially consumes butadiene. On exhaustion of this monomer, the reaction speeds up and then styrene polymerizes rapidly. This peculiar behaviour, which was originally explained by Korotkov by treating the monomers as solvents, butadiene being a preferential solvent for the Li⁺ cation, was later accounted for by considering the cross-over reactions. In this paper an in dept further explanation is given by admitting that the polymerization reactions occur through coordination of the Li ⁺ cation by the monomer followed by insertion of the monomer into the polymer chain. A preliminary MOPAC 93 (PM3) calculation seems to confirm this interpretation.     

An improved method for the polymerization of ethynylferrocene. Conducting properties of doped polyethynylferrocene

The catalytic activity of the [Rh(cod)Cl]₂ complex (cod  cis, cis-cyclo-octa-1,5-diene) with respect to the polymerization of ethynylferrocene (EFc) was examined. A good yield (about 80%) of polyethynylferrocene (PEFc) was obtained in benzene by addition of sodium hydroxide as co-catalyst. PEFc was insoluble in most organic solvents. The conductivity (s̀) of the undoped polymer is about 10⁻¹¹ ohm⁻¹ cm⁻¹; upon doping PEFc with iodine in tetrahydrofuran the conductivity can be increased to 10-100 ohm⁻¹ cm⁻¹. The influence of other doping agents was also examined.     

Sodium Carbazolide and Derivatives as Solid-State Electrolytes for Sodium-Ion Batteries

Replacing widely used organic liquid electrolytes with solid-state electrolytes (SSEs) could effectively solve the safety issues in sodium-ion batteries. Efforts on seeking novel solid-state electrolytes have been continued for decades. However, issues about SSEs still exist, such as low ionic conductivity at ambient temperature, difficulty in manufacturing, low electrochemical stability, poor compatibility with electrodes, etc. Here, sodium carbazolide (Na-CZ) and its THF-coordinated derivatives are rationally fabricated as Na⁺ conductors, and two of their crystal structures are successfully solved. Among these materials, THF-coordinated complexes exhibit fast Na⁺ conductivities, i.e., 1.20×10⁻⁴ S cm⁻¹ and 1.95×10⁻³ S cm⁻¹ at 90 °C for Na-CZ-1THF and Na-CZ-2THF, respectively, which are among the top Na⁺ conductors under the same condition. Furthermore, stable Na plating/stripping is observed even over 400 h cycling, showing outstanding interfacial stability and compatibility against Na electrode. More advantages such as ease of synthesis, low-cost, and cold pressing for molding can be obtained. In situ NMR results revealed that the evaporation of THF may play an essential role in the Na⁺ migration, where the movement of THF creates defects/vacancies and facilitates the migration of Na⁺.     

Kinetics and mechanism of the anionic polymerization of cyclohexadienes initiated by naphthalene radical anions and dianions

The anionic polymerization of 1.3-cyclohexadiene (1.3-CHD) was investigated in temperatures that ranged from 25 to ?77°C. Initiation by lithium naphthalene (N^?·,Li⁺) in tetrahydrofuran at ?20°C yields polymers with fairly narrow molecular weight distribution. The M?_w of these polymers so prepared is ca. 20,000. Polymerization of 1.3-CHD conducted at room temperature is accompanied by the dehydrogenation and disproportionation of the monomer, especially when N^?·,K⁺ acts as initiator. Oligomers are formed when hexamethylphosphoramide is used as a solvent. The mechanism of the initiation of the polymerization of 1.3-CHD by N^?·,Li⁺ was elucidated and the rate constants at ?20°C in tetrahydrofuran of the elementary reactions were determined. It was established that the dianions formed by disproportionation of N^?·,Li⁺ act as effective initiators for 1.3-CHD. The adducts formed constitute the cyclohexanyl and naphthyl carbanionic groups. The former carbanions (λ_max ～ 275 nm) propagate the polymerization. The initially formed dimeric adducts are stabilized by the separation of the carbanionic end groups by the additional monomer units. Chain transfer to the monomer limits the growth of the polymers. The isomerization of the cyclohexadienyl anions, formed as result of chain transfer, may be followed by the elimination of lithium hydride. The latter reaction represents a termination step. Addition of 1.4-CHD to the reaction mixture enhances the chain transfer and the termination.     

Ordered and Fast Ion Transport of Quasi-solid-state Electrolyte with Regulated Coordination Strength for Lithium Metal Batteries

Polymer based quasi-solid-state electrolyte (QSE) has attracted great attention due to its assurance for high safety of rechargeable batteries including lithium metal batteries (LMB). However, it faces the issue of low ionic conductivity of electrolyte and solid-electrolyte-interface (SEI) layer between QSE and lithium anode. Herein, we firstly demonstrate that the ordered and fast transport of lithium ion (Li⁺) can be realized in QSE. Due to the higher coordination strength of Li⁺ on tertiary amine (−NR₃) group of polymer network than that on carbonyl (−C=O) group of ester solvent, Li⁺ can diffuse orderly and quickly on −NR₃ of polymer, significantly increasing the ionic conductivity of QSE to 3.69 mS cm⁻¹. Moreover, −NR₃ of polymer can induce in situ and uniform generation of Li₃N and LiN_xO_y in SEI. As a result, the Li||NCM811 batteries (50 μm Li foil) with this QSE show an excellent stability of 220 cycles at ≈1.5 mA cm⁻², 5 times to those with conventional QSE. LMBs with LiFePO₄ can stably run for ≈8300 h. This work demonstrates an attractive concept for improving ionic conductivity of QSE, and also provides an important step for developing advanced LMB with high cycle stability and safety.     

Polymerized ionic liquids: Effects of counter‐anions on ion conduction and polymerization kinetics

A novel imidazolium‐containing monomer, 1‐[ω‐methacryloyloxydecyl]‐3‐(n‐butyl)‐imidazolium (1BDIMA), was synthesized and polymerized using free radical and controlled free radical polymerization followed by post‐polymerization ion exchange with bromide (Br), tetrafluoroborate (BF₄), hexafluorophosphate (PF₆), or bis(trifluoromethylsulfonyl)imide (Tf₂N). The thermal properties and ionic conductivity of the polymers showed a strong dependence on the counter‐ions and had glass transition temperatures (T_g) and ion conductivities at room temperature ranging from 10 °C to −42 °C and 2.09 × 10⁻⁷ S cm⁻¹ to 2.45 × 10⁻⁵ S cm⁻¹. In particular, PILs with Tf₂N counter‐ions showed excellent ion conductivity of 2.45 × 10⁻⁵ S cm⁻¹ at room temperature without additional ionic liquids (ILs) being added to the system, making them suitable for further study as electro‐responsive materials. In addition to the counter‐ions, solvent was found to have a significant effect on the reversible addition‐fragmentation chain‐transfer polymerization (RAFT) for 1BDIMA with different counter‐ions. For example, 1BDIMATf₂N would not polymerize in acetonitrile (MeCN) at 65 °C and only achieved low monomer conversion (< 5%) at 75 °C. However, 1BDIMA‐Tf₂N proceeded to high conversion in dimethylformamide (DMF) at 65 °C and 1BDIMABr polymerized significantly faster in DMF compared to MeCN. NMR diffusometry was used to investigate the kinetic differences by probing the diffusion coefficients for each monomer and counter‐ion in MeCN and DMF. These results indicate that the reaction rates are not diffusion limited, and point to a need for deeper understanding of the role electrostatics plays in the kinetics of free radical polymerizations. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018 , 56, 1346–1357