单离子聚合物快离子导体.pdf

物 理 化 学 学 报 Acta Phys.-Chim.Sin.2023,39(8),2205012(1 of 10)Received:May 6,2022;Revised:May 26,2022;Accepted:May 27,2022;Published online:June 9,2022.*Corresponding authors.Emails:(Y.S.);(L.C.).This project was supported by the National Key Research and Development Program of China(2021YFB3800300)and the National Natural Science Foundation of China(21733012,22179143).国家重点研究发展项目(2021YFB3800300)和国家自然科学基金(21733012,22179143)资助 Editorial office of Acta Physico-Chimica Sinica Article doi:10.3866/PKU.WHXB202205012 A Single-Ion Polymer Superionic Conductor Guoyong Xue 1,2,Jing Li 2,Junchao Chen 3,Daiqian Chen 2,Chenji Hu 2,3,Lingfei Tang 1,2,Bowen Chen 1,2,Ruowei Yi 2,Yanbin Shen 1,2,*,Liwei Chen 2,3,*1 School of Nano-Tech and Nano-Bionics,University of Science and Technology of China,Hefei 230026,China.2 i-Lab,CAS Center for Excellence in Nanoscience,Suzhou Institute of Nano-Tech and Nano-Bionics,Chinese Academy of Science,Suzhou 215123,Jiangsu Province,China.3School of Chemistry and Chemical Engineering,Shanghai Jiaotong University,Shanghai 200240,China.Abstract:All-solid-state batteries(ASSBs)have been considered a promising candidate for the next-generation electrochemical energy storage because of their high theoretical energy density and inherent safety.Lithium superionic conductors with high lithium-ion transference number and good processability are imperative for the development of practical ASSBs.However,the lithium superionic conductors currently available are predominantly limited to hard ceramics.Practical lithium superionic conductors employing flexible polymers are yet to be realized.The rigid and brittle nature of inorganic ceramic electrolytes limits their application in high-performance ASSBs.In this study,we demonstrate a novel design of a ternary random copolymer single-ion superionic conductor(SISC)through the radical polymerization of three different organic monomers that uses an anion-trapping borate ester as a crosslinking agent to copolymerize with vinylene carbonate and methyl vinyl sulfone.The proposed SISC contains abundant solvation sites for lithium-ion transport and anion receptors to immobilize the corresponding anions.Furthermore,the copolymerization of the three different monomers results in a low crystallinity and low glass transition temperature,which facilitates superior chain segment motion and results in a small activation energy for lithium-ion transport.The ionic conductivity and lithium-ion transference number of the SISC are 1.29mScm1 and 0.94 at room temperature,respectively.The SISC exhibits versatile processability and favorable Youngs modulus(3.4 0.4 GPa).The proposed SISC can be integrated into ASSBs through in situ polymerization,which facilitates the formation of suitable electrode/electrolyte contacts.Solid-state symmetric Li|Li cells employing in situ polymerized SISCs show excellent lithium stripping/plating reversibility for more than 1000 h at a current density of 0.25 mAcm2.This indicates that the interface between the SISC and lithium metal anode is electrochemically stable.The ASSBs that employ in situ polymerized SISCs coupled with a lithium metal anode and various cathodes,including LiFePO4,LiCoO2,and sulfurized polyacrylonitrile(SPAN),exhibit acceptable electrochemical stability,including high rate performance and good cyclability.In particular,the Li|LiFePO4 ASSBs retained 70%of the discharge capacity when the charge/discharge rate was increased from 1 to 8C.They also demonstrate long-term cycling stability(700cycles at 0.5C rate)at room temperature.A capacity retention of 90%was achieved even at a high rate of 2C after 300 cycles at room temperature.Furthermore,the SISCs have been applied to Li|LiFePO4 pouch cells and exhibit exceptional flexibility and safety.This work provides a novel design principle for the fabrication of polymer-based superionic conductors and is valuable for the development of practical ambient-temperature ASSBs.Key Words:All-solid-state lithium metal battery;Solid polymer electrolyte;Superionic conductor;Single-ion conductor;In situ polymerization;Rate performance 物理化学学报 Acta Phys.-Chim.Sin.2023,39(8),2205012(2 of 10)单离子聚合物快离子导体单离子聚合物快离子导体 薛国勇1,2，李静2，陈俊超3，陈代前2，胡晨吉2,3，唐凌飞1,2，陈博文1,2，易若玮2，沈炎宾1,2,*，陈立桅2,3,*1中国科学技术大学纳米技术与纳米仿生学院，合肥 230026 2中国科学院苏州纳米技术与纳米仿生研究所，创新实验室卓越纳米科学中心，江苏 苏州 215123 3上海交通大学化学化工学院，上海 200240 摘要：摘要：具有高锂离子迁移数和良好可加工性能的锂快离子导体对于全固态电池的发展非常重要。然而，现有的锂快离子导体主要限制于硬质陶瓷，目前尚无柔性聚合物类型的锂快离子导体被报道。在这个工作中，我们报告了一种通过三种不同有机单体的自由基聚合反应形成的三元无规共聚单离子快离子导体(SISC)。该SISC中包含丰富的锂离子传输位点和具有阴离子锚定功能的阴离子受体。此外，三种不同单体的共聚反应带来低结晶度和低玻璃化转变温度(Tg)，有利于链段运动，从而获得小的锂离子传输的活化能(Ea)。电化学测试结果表明，该SISC的室温离子电导率和锂离子迁移数分别达到1.29mScm1和0.94。将SISC与锂金属负极和多种正极(包括LiFePO4、LiCoO2和硫化聚丙烯腈(SPAN)原位聚合，组装得到的全固态电池具有良好的电化学稳定性。其中，Li|LiFePO4全固态电池表现出高达8C的倍率性能和良好的循环寿命(在0.5C倍率下稳定循环 700圈)。这项工作提供了一种新颖的聚合物基快离子导体设计理念，对于发展高性能全固态电池具有重要意义。关键词：关键词：全固态锂金属电池；聚合物固态电解质；超离子导体；单离子导体；原位聚合；倍率性能 中图分类号：中图分类号：O646 1 Introduction Replacing flammable organic electrolytes in commercial Li-ion batteries with solid state electrolyte(SSE)to assemble all-solid-state batteries(ASSBs)is believed to be the ultimate solution for addressing the safety issue of Li-ion batteries 1,2.Ideally,SSEs should have a high room-temperature(RT)ionic conductivity and good contact with the electrode materials to ensure a fluent Li-ion transportation through the entire battery,a large lithium-ion transference number(tLi+)to avoid serious ionic concentration polarization during high power charge/discharge,and a wide electrochemical stability window to enable the use of high energy density electrode materials 24.However,it is a challenge to develop a SSE to meet all these requirements.Ceramic electrolytes usually have a high RT ionic conductivity,a large tLi+close to unity,and a wide electrochemical stability window,but they often suffer from large electrode|electrolyte interfacial resistance and poor processibility due to their rigid and brittle nature,restricting their practical application in ASSBs 5,6.By contrast,solid polymer electrolytes(SPEs)are flexible and processable 7.Importantly,they might be prepared by in situ polymerization during battery assembly to ensure a small electrode|electrolyte interfacial resistance 3,8.Nevertheless,most SPEs suffer from low RT ionic conductivity(106104 Scm1)and small lithium-ion transference number(tLi+0.5)912.To obtain a decent electrochemical performance of ASSBs for practical applications,the RT ionic conductivity of the SPE should exceed 104 Scm1,and the tLi+should be as close to unity as possible 12.Therefore,over the past few decades,extensive efforts have been devoted to enhancing the RT ionic conductivity and the tLi+of SPEs 12,13.The ionic conductivity of SPEs is mainly affected by the number of Li+solvation sites,the dissociation ability of Li+of the functional groups,and the polymer chain motion 1418.There-fore,copolymerization or crosslinking of functional units 3,19,20,nano-filler doping 2123,and addition of plasticizer 2426 have been used to increase the ionic conductivity of SPEs 27.On the other hand,organic/inorganic hybrids 28,polyanions 29,30,and anion acceptor-containing polymers 31 have been used to inhibit the movement of anions and boost the Li+dissolution,obtaining a high tLi+of SPEs.Progresses have been made in the past years on either the ionic conductivity or the tLi+of SPEs.For example,Lin et al.32 developed a poly(vinyl ethylene carbonate)(PVEC)based polymer electrolyte via a polymerization process and obtained a superior RT ionic conductivity of 2.1 103 Scm1,but the tLi+is at a relatively low value of 0.4.Shin et al.33 reported a processable single-ion conducting borate polymer consisting of weakly coordinating borate anions connected through butenediol linkers,which shows exceptional selectivity for Li-ion conduction(tLi+=0.95),however,the RT ionic conductivity is limited at 1.5 104 Scm1 even in the presence of 30%(mass fraction)polar solvating plasticizer(propylene carbonate).Therefore,it is still an outstanding challenge to develop high quality SPEs with both high RT ionic conductivity(103 Scm1)and high tLi+approaching unity.Herein,we have designed a novel ternary random copolymer 物理化学学报 Acta Phys.-Chim.Sin.2023,39(8),2205012(3 of 10)single-ion superionic conductor(SISC),dubbed as P(M-B-V)(Scheme 1).The P(M-B-V)exhibits both high RT ionic conductivity(103 Scm1)and high tLi+approaching unity.It can either be prepared into a free-standing film to ensure mechanical strength or be prepared via in situ polymerization during battery assembly to a low resistant electrode|electrolyte interface,therefore resulting in ASSBs with excellent rate capability and stable cyclability.2 Experimental section 2.1 Materials 2-hydroxyethyl methacrylate(HEMA;97%),trimethyl borate(TMB;99%),and methyl vinyl sulfone(MVS;95%)were purchased from Adamas(Shanghai)and used as received.Vinylene carbonate(VC;DoDoChem(Suzhou),2,2-azobisisobutyronitrile(AIBN;Aladdin(Shanghai),bis(trifluoromethanesulfonyl)imide lithium(LiTFSI;DoDoChem),anhydrous acetonitrile(Adamas),TF cellulose membrane(NKK(Japan),LiFePO4(LFP;Sinlion Battery Tech,Co.,Ltd.(Suzhou),LiCoO2(LCO;XTC Corp(Xiamen),sulfur powder(S;99.9%,Sigma-Aldrich(Shanghai),acrylonitrile(AN;Aladdin),acetylene black(AB;Alfa Aesar(Tianjin),poly(vinyl difluoride)(PVDF;Aladdin),poly(ethylene oxide)(PEO;Mv=400000,Sigma-Aldrich),N-methyl pyrrolidone(NMP;99.5%,Aladdin),and LiTFSI were dried under vacuum at 100 C for 48 h,and the TF cellulose film was dried under vacuum at 80 C for 24 h and stored in an argon-filled glove box prior to use.2.2 Synthesis of boron-based crosslinking agent(BTETM)34 A mixture of TMB(0.52 g,5 mmol)and HEMA(2.05 g,15.75 mmol)was dissolved in 10 mL anhydrous acetonitrile,and the solution was stirred at 50 C for 3 h in an argon-filled glove box.Subsequently,the solution was transferred to a reaction device ventilated with argon,and it was continuously stirred at 70 C for another 3 h to remove methanol produced as a by-product.Finally,the obtained raw product was distilled at 65 C under reduced pressure to remove unreacted TMB and residual acetonitrile,and it was then dried under high vacuum conditions at 30 C for 48 h.The resultant dried(boranetriyltris(oxy)tris(ethane-2,1-diyl)tris(2-methylacrylate)(BTETM)was quickly transferred to an argon-filled glove box for storage to prevent possible hydrolysis.The product was characterized by 1Hnuclear magnetic resonance(1H-NMR)and 11B nuclear magnetic resonance(11B-NMR)spectroscopy(as shown in Fig.S1).1H-NMR 400 MHz,CDCl3,TMS ref of BTETM:6.11(vinyl,CH),5.56(vinyl,CH),4.23(CH2OC(O),4.01(CH2)OB),1.94(isobutyl,CH3).11B-NMR 400 MHz,CDCl3,TMS ref of BTETM:18.02(BO).2.3 Preparation of P(M-B-V)SISC A solution mixture containing MVS,BTETM,and VC with a certain mass ratio was evenly mixed under magnetic stirring at room temperature.Then,an appropriate amount of LiTFSI(20%(mass fraction)of total monomers)was dissolved in the above solution.After 2,2-azobisisobutyronitrile(AIBN)(1%(mass fraction)of total monomers)was added and stirred for 1.5 h,the precursor solution was injected into a cellulose membrane(18 mm)and followed by heating at 70 C for 20 h.All these processes were conducted in an argon-filled glove box.2.4 Preparation of all-solid-state Li|P(M-B-V)|LFP(LCO)battery LFP(LCO),AB,and PVDF powders with a weight ratio of 80:10:10 were mixed in NMP solvent under vigorous magnetic stirring overnight.Then,the slurry was cast on an aluminum foil and dried at 80 C for 12 h under a vacuum.The areal loading of the LFP(LCO)cathode was 1.151.50 mgcm2.Subsequently,the electrolyte precursor solution composed of MVS,BTETM,VC,LiTFSI,and AIBN was injected into the cellulose membrane(18 mm),which was then placed on top of the LFP(LCO)cathode and pasted with Li foil(China Energy Lithium Co.Ltd.(Tianjin).Finally,the three-layer sandwich structure was sealed in a 2032 coin cell and kept constantly at 70 C for 20 h.All these processes were conducted in an argon-filled glove box.2.5 Preparation of all-solid-state Li|P(M-B-V)|SPAN battery The sulfurized polyacrylonitrile(SPAN)cathode was prepared based on our previous work and relevant literature 35,36 with an areal loading of approximately 2.00 mgcm2.The battery assembly process was similar to the all-solid-state Scheme 1 Schematics for P(M-B-V)prepared via free-radical random co-polymerization.物理化学学报 Acta Phys.-Chim.Sin.2023,39(8),2205012(4 of 10)Li|P(M-B-V)|LFP(LCO)battery described above.2.6 Preparation of all-solid-state Li|P(M-B-V)|LFP pouch-type battery The flexible Li|LFP pouch cell with LFP areal loading of 4.0 mgcm2 was fabricated via in situ polymerization similar as above.The size of the cathode electrode was 2.50 cm 2.00 cm.2.7 Preparation of Li+block battery LFP and PVDF powders with a weight ratio of 80:10 were mixed in NMP solvent under vigorous magnetic stirring overnight.Then,the slurry was cast on aluminum foil and dried at 80 C for 12 h under a vacuum.The areal loading of the LFP cathode was 6.16 mgcm2.Next,the electrolyte precursor solution composed of MVS,BTETM,VC,LiTFSI,and AIBN was added to the cathode,which was then placed on top of the cathode and pasted with stainless steel(SS).Finally,the three-layer sandwich structure was sealed in a 2032 coin cell and kept constantly at 70 C for 20 h.All these processes were conducted in an argon-filled glove box.2.8 Characterization methods Nuclear magnetic resonance(NMR)measurements were performed on a Varian Mercury Plus 400 MHz spectrometer and Bruker 400 MHz spectrometer.The morphology and elemental distribution of solid polymer electrolyte(SPE)samples were analyzed through scanning electron microscopy(SEM;FEI Quanta 400 FEG)equipped with energy dispersive X-ray spectrometry(EDX).A Thermo Scientific Nicolet 6700 spectrometer was used to collect Fourier transform infrared(FTIR)spectra of the samples.The crystallinity of the samples was investigated using X-ray diffraction(XRD)measurements on a D8 diffractometer(Bruker)with Cu K radiation in the 2 range of 2080.Thermogravimetric analysis(TGA;TG/DTA6300)was conducted under a nitrogen atmosphere at a heating rate of 10 Cmin1 in the temperature range of 30-600 C.Differential scanning calorimetry(DSC;DSC6220)analysis was performed in the temperature range of 80 to 80 C with a heating rate of 10 Cmin1.The Raman spectra were acquired using a Renishaw in via Qontor confocal Raman microscope using a 785/532 nm wavelength laser.The mechanical properties of the samples were measured by a Universal Material Tester Instron 3365 in the range of 010 N.The Youngs modulus was measured by atomic force microscopy(AFM;Asylum Research Cypher S AFM)and AC160TS-R3 tip(Olympus).The Sneddon model was used to fit the force curves.Spots were randomly picked on a selected region,and the value of Youngs modulus within a specific range was measured.2.9 Electrochemical measurements The ionic conductivity of the SPE samples was measured by alternating current(AC)impedance on a symmetric SS|SPE|SS ce