稀有金属(英文版) 2021,40(01),65-71

Realizing simultaneously enhanced energy and power density fullcell construction using mixed hard carbon/Li₄Ti₅O₁₂ electrode

Shi-Fei Huang Yao Lv Da Tie Yang Yu Yu-Feng Zhao

State Key Laboratory of Metastable Materials Science and Technology,Key Laboratory of Applied Chemistry,Yanshan University

Institute of Sustainable Energy,Shanghai University

作者简介：Yu-Feng Zhao e-mail:yufengzhao@ysu.edu.cn;

收稿日期：26 October 2018

基金：financially supported by the National Natural Science Foundation of China (No.51774251);Hebei Natural Science Foundation for Distinguished Young Scholars (No. B2015203096);the Hundred Excellent Innovative Talents Support Program in Hebei Province (No.SLRC2017057);the Scientific Research Foundation for the Returned Overseas Chinese Scholars (No.CG2014003002);the Open Funding from State Key Laboratory of Advanced Chemical Power Sources (No.SKL-ACPS-C-11);

Realizing simultaneously enhanced energy and power density fullcell construction using mixed hard carbon/Li₄Ti₅O₁₂ electrode

Shi-Fei Huang Yao Lv Da Tie Yang Yu Yu-Feng Zhao

State Key Laboratory of Metastable Materials Science and Technology,Key Laboratory of Applied Chemistry,Yanshan University

Institute of Sustainable Energy,Shanghai University

Abstract：

Practical applications of lithium-ion batteries(LIBs) with both high energy and power density are urgently demanded,which require suitable charge/discharge platform,fast charge-transfer kinetics,as well as optimal solid electrolyte interphase(SEI) layer of electrode materials.In this work,a high-performance lithium-ion battery(LIB) full cell was assembled by using commercial LiNi_0.33Co_0.33Mn_0.33O₂(NCM111) as the positive electrode and mixed Li₄ Li₅ O₁₂(LTO)/hard carbon(HC) as the negative electrode.It reveals that the component ratio between LTO and HC plays a critical role in manipulating the electric conductivity and the electro-reaction platform.The electrochemical test results show that when the content of HC is 10 wt%,the as-constructed full cell demonstrates the best electrochemical,with a maximum energy density of 149.2 Wh·kg^-1 and a maximum power density of2195 W·kg^-1 at 10 A·g^-1(30 C).This outperforms all the assembled systems within our work range and the state-ofthe-art literatures.The NCM//Li₄ Ti₅ O₁₂+10 wt% HC battery system also exhibits a good capacity retention after1000 cycles at the current density of 1 A·g^-1.This work provides a new approach to enhance the full-cell performance by mixing electrode materials with different charge potentials and reaction kinetics.

Keyword：

Hard carbon; NCM111; LTO/HC; Lithium-ion battery;

Received： 26 October 2018

1 Introduction

Li-ion batteries (LIBs) are the mainstream energy storage devices for today's electric/hybrid vehicles and portable devices [ 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14] .LIBs with graphite anode and the traditional cathode electrode (LiMn₂O₄,LiCoO₂,LiFePO₄)typically demonstrate a high energy density(150-200 Wh·kg-1).However,the application is limited to a relatively low power density (<500 W·kg^-1) and poor cycle performance (<1000 cycles) [15 ^{[15,16,17,18]}8] .Thus,new type lithium-ion battery systems with high power density and high energy density are urgently demanded.

As a branch of anode materials of LIBs,Li₄Ti₅O₁₂(LTO) is a“zero-strain”insertion electrode material (only slight volume change of 0.2%was observed during the cycle) with theoretical capacity of 175 mAh·g^-1,relatively high redox potential (1.55 V vs.Li⁺/Li) and better rate performance than graphite [ 19, 20, 21] .Thus,LTO represents an ideal candidate for LIB negative electrode materials with long cycle life and high rate performance [ 22, 23, 24] .On the other hand,layered transition metal oxides LiMO₂(M=Ni,Co,Mn) generally possess high voltage platform and high theoretical specific capacity (～270 mAh·g^-1),revealing a superior electrochemical and safety performance among the different types of positive electrode materials [ 25, 26, 27] .Nevertheless,LTO shows poor intrinsic conductivity as metal oxides,which easily leads to chargetransfer kinetics delay and limited power density of the full cell.Besides,the relatively higher redox potential (1.55 V vs.Li⁺/Li) of LTO anode would restrict the operating potential window of the full cells,thus affecting the energy density.Note that hard carbon (HC) is a kind of excellent LIB electrode material,which not only has good conductivity and high lithium storage capacity,but also shows low potential versus Li [ 1, 28, 29] .Therefore,it is reasonable to assume by mixing LTO with HCs could effectively solve the charge-transfer kinetics retardation problem.What's more,the charge/discharge potential vs.Li also can be balanced with a certain degree.

Herein,we assembled LIBs by using LiNi_0.33Co_0.33Mn_0.33O₂ (NCM11) as the positive electrode and LTO/HC as the negative electrode,respectively.The introduction of hard carbon in LTO can not only effectively solve the charge-transfer kinetics and Li-ion diffusion rate problems but also can greatly improve the energy density,power density and cyclic stability of the electrode materials.The results show that the NCM111/LTO+HC-type battery system exhibits more excellent cycle and rate performance when HC incorporation amount is 10 wt%.This work provides a new approach to enhance the full-cell performance by mixing electrode materials with different charge potential and reaction kinetics.

2 Experimental

2.1 Materials

Commercial NCM111 (74μm,China,BTR,New Energy Meterial,INC),commercial LTO (Ke Jing,China) and polyvinylidene fluoride (PVDF) binder (Ke Jing,China) in N-methyl-2-pyrrolidone (NMP)(Ke Jing,China) were used.

2.2 Li4Ti5O12/HC preparation

The hard carbon was synthesized as described in the previous work [ 1] .The Li₄Ti₅O₁₂/HC electrode were prepared by mixing 0 wt%,5 wt%,10 wt%,20 wt%and 30 wt%synthesized hard carbon materials with Li₄Ti₅O₁₂ which were donated as LTO+0 wt%HC,LTO+5 wt%HC,LTO+10 wt%HC,LTO+20 wt%HC,LTO+30wt%HC,respectively.

2.3 Electrochemical measurements

The mass ratio between LiNi_0.33Co_0.33Mn_0.33O₂/acetylene black/PVDF was controlled as 80 wt%:10 wt%:10 wt%and Li₄Ti₅O₁₂/HC/Surper P/PVDF to 80 wt%:10 wt%:10 wt%,respectively.The electrode materials were scattered uniformly in N-methyl pyrrolidone (NMP) turning into slurry,and evenly coated in aluminum foil (the cathode) and copper foil (anode) in the preparation of the positive and negative electrodes.According to the formula C_N/C_P (where C_N/C_P is the proportion of the negative design capacity and positive design capacity,which was commonly used parameter to evaluate electrodes in lithium-ion battery manufacturing method),the mass ratio of positive and negative active substances was designed.Finally,1 mol-L^-1 LiPF₆/ethylene carbonate (EC)/diethyl carbonate (DEC)/dimethyl carbonate (DMC)(volume ratio of 1:1:1) was used as electrolyte,and CR2032 steel shell was used as battery shell.The full battery was assembled in the Ar atmosphere glove box (water content of 0.01×l0^-6 and O₂ content of0.01×10^-6).Cyclic voltammetry (CV) curves and electrochemical impedance spectroscopy (EIS) spectra were measured at the scanning rate of 0.1 mV·s^-1 and the frequency range of 0.01 to 1×10⁵ Hz on CHI650e electrochemical workstation (Chenhua,China),respectively.And,the galvanostatic charge-discharge was tested through Land CT2001A equipment (China) in the potential rage of1.5-3.0 V.

2.4 Characterization

The RIGAKU/max-2500/PC type X-ray powder diffractometer (XRD) with Cu Ka radiation (λ=0.154 nm)operated at 40 kV,200 mA was adopted to characterize the structure and phase of the sample at the scanning speed of 4(°)-min^-1.The morphology and internal microstructure of the samples were characterized using Carl Zeiss SUPRA 55SAPPHIRE field emission scanning electron microscopy(FESEM),Hitachi-7650 projection transmission electron microscopy (TEM,Japan,80 kV) and high-resolution transmission electron microscopy (HRTEM,JEOL JEM-3000f).The electrochemical test was carried out by using the electrochemical workstation (China,Chenghua,CHI650E) at the speed of 0.1 mV·s^-1 by cyclic voltammetry method.The charge-discharge rate and cycle performance were tested by LAND test system (China,Wuhan Rand Electronics Co.,LTD.,CT2001A).The potential window of all electrochemical tests was operated at1.5-3.0 V.

3 Results and discussion

3.1 Characterization

XRD,scanning electron microscope (SEM),TEM,HRTEM and selected area electron diffraction (SAED)were employed to study the microstructure and composition of the samples.A sharp peak (002) at26=26.40°(slightly smaller than the (002) peak of graphite (20=26.54°)) indicates the characteristic peaks of graphitic lattice in the partially graphitized samples,which gives ad-spacing of 0.3373 nm and indicates an expanded interlayer according to the Bragg equation (Fig.la).However,XRD patterns of HCs show a broad Bragg reflection at around 25°((002)) and a weak reflection centered around 43°((100) and (101)),which can be assigned to the amorphous carbon structures in the partially graphitized samples [ 30] .As shown in SEM and TEMimages of HCs (Fig.1b,c),the architecture of the HCs possesses unique interconnected carbon nanoshell with the diameter size of?200-600 nm and the thickness of?20-50 nm.And from HRTEM images of HCs,the turbostratic carbon structure,ordered nanographite domains(with nanovoids surrounded by some parallel carbon hexagonal layers),microporous,defects and crisscrossed graphene layers in the shells of HCs can be seen clearly.The layer-to-layer distance of d(002) is about0.347-0.400 nm,which is confirmed by (002) XRD peak(Fig.Id).Furthermore,the nanographite domains with graphene stripes and defects can not only improve the conductivity of materials but also provide a large number of energy storage sites for Li⁺.Meanwhile,SAED pattern(Fig.le) also shows the bright diffraction rings of (002)and (101) planes of HCs,proving that the good degree graphitization of the materials.The analysis results are also consistent with the above HRTEM and XRD conclusions well.Finally,the typical representation SEM pictures of NCM111 and LTO are also provided and shown in Fig.1f,g,respectively.And the corresponding XRD diagrams of pure NCM111 and LTO samples are shown in Fig.S1.The main diffraction peaks of commercial NCM111 and LTO correspond to the indexed PDF standard cards,respectively,with good crystallinity.

SEM images of LTO doped with 10 wt%HC are also shown in Fig.2.Precisely,the irregular particles with size of～0.5-20μm for LTO are shown in the corresponding SEM images.And the uniform distribution of hard carbon can be seen in LTO particle gaps and surfaces.The addition of HCs can not only improve the conductivity of the electrode,but also provide additional energy storage sites,thus improving the electrochemical performance of the electrode.

Fig.1 a XRD pattern of synthesized hard carbons;b SEM,c TEM,d HRTEM images (embedded being the corresponding layer spacing measurement chart) and e SAED patterns of synthesized hard carbons;SEM images of f NCM111 and g LTO

Fig.2 SEM images of LTO+10 wt%HC

3.2 Electrochemical performances

To study the effect of hard carbon on the electrochemical properties of electrode materials,we assembled the full battery by controlling the hard carbon content of the anode and cathode materials,and the electrochemical test results are shown in Fig.3.Promisingly,among all assembled full-cell systems and the state-of-the-art literatures(Fig.3a,b and Table l),NCM111/LTO+10 wt%HC delivers the highest energy density of 149.2 Wh·kg-1 at the current density of 0.1 A-g^-1 and the highest power density of 2195 W-kg^-1 at 10 A·g^-1.Figure 3c,d shows the discharge curves of the NCM111/LTO+0 wt%HC,NCM111/LTO+5 wt%HC,NCM111/LTO+10 wt%HC,NCM111/LTO+20 wt%HC and NCM111/LTO+30 wt%HC at the current density of 0.1 A·g^-1 and rate performance of NCM111/LTO+0 wt%HC,NCM111/LTO+5 wt%HC,NCM111/LTO+10 wt%HC,NCM111/LTO+20 wt%HC,NCM111/LTO+30 wt%HC with the operating potential of 1.5-3.0 V,respectively.The more stable and longer discharge platforms of NCM111/LTO+10 wt%HC full battery system are shown in Fig.3c,which can be attributed to that the introduction of hard carbon can not only provide more active sites for lithium storage but also increase the working potential for the full battery to a certain extent and greatly improve the lithium storage capacity.Meanwhile,the uniformly mixed hard carbon and LTO form a uniform conductive network,which greatly improves the charge-transfer kinetics of electrode materials and thus increases rate performance(Fig.3d).However,with the introduction of more carbon materials,more SEIs will be formed during the reaction process,leading to the consumption of electrolyte,which will affect the performance of the battery (Fig.3d).

Fig.3 a Maximum energy density (P_max) and b maximum power density (E_max) of NCM111/LTO+HC system;c discharge curves of NCM111/LTO+HC at current density of 0.1 A·g^-1 with operate potential of 1.5-3.0 V;d rate performance of NCM111/LTO+HC system

  下载原图

Table 1 Comparison of operate potential,maximum energy density and maximum power density of different battery systems

In order to further study the electrochemical performance of NCM11/LTO+10 wt%HC,a series of electrochemical tests such as CV,long cycle performance and EIS are also provided,respectively (Fig.4).The reversible peaks at around 2.10 and 2.45 V during the discharge process in the CV curves of NCM111/LTO+10 wt%HC can be attributed to the reaction of NCM111-LTO and NCM111-HC,respectively (Fig.4a).The low potential of HCs vs.Li makes high charge/discharge platform of the full-cell system,which can greatly increase the energy density of NCM111/LTO+10 wt%HC full battery(Fig.4b,c).

Furthermore,the cycle performance of NCM111/LTO+10 wt%HC and NCM111/LTO+0 wt%HC was also tested at the current density of 1 A·g^-1,respectively(Fig.4d).The capacity retention rate of NCM111/LTO+10 wt%HC can be maintained as 75%after the cycle of500th,and even 56%after the cycle of 1000th.However,the capacity retention of NCM111/LTO+0 wt%HC battery is only 40%after the cycle of 500th.Meanwhile,a faster charge-transfer kinetics (a small semicircle and x-intercept) and the better Li-ion diffusion rates (Warburgtype line (the slope of the 45℃region of the plots) on the real axis is shorter) of NCM111/LTO+10 wt%HC than NCM111/LTO+0 wt%HC also can be indicated from EIS spectra (Z'is the real part of the impedance and-Z''is the imaginary part of the impedance)(Fig.4e).Thus,the above results also indicate that the introduction of hard carbon in LTO can not only effectively solve the chargetransfer kinetics and Li-ion diffusion rate problems but also can greatly improve the energy density,power density and cyclic stability of the electrode materials.Finally,the light emitting diodes (LED) can be lit for 5 min at last,which proves the practical application value of the NCM111/LTO+10 wt%HC-type battery system (Fig.4f).

Fig.4 a CV curves of NCM111/LTO+10 wt%HC at a scan rate of 0.5 mV-s^-1;CV curves of NCM111/LTO+0 wt%HC at a scan rate of0.5 mV·s^-1;c CV curves of NCM111/LTO+10 wt%HC and NCM111/LTO+0 wt%HC at second cycles with a scan rate of 0.5 mV·s^-1;d cycle performance of NCM111/LTO+10 wt%HC and NCM111/LTO+0 wt%HC at current density of 1 A·g^-1;e EIS curves of NCM111/LTO+10 wt%HC and NCM111/LTO+0 wt%HC;f photograph of a LED being powered by a NCM111/LTO+10 wt%HC full cell

4 Conclusion

In summary,through regulating the ratio between HC and LTO,we assembled a high-performance lithium-ion battery full cell to obtain new devices with high capacity,good rate performance and cyclic stability.The results show that the NCM111/LTO+HC-type battery system exhibits more excellent cycle and rate performance when HC incorporation amount is 10 wt%.Under the current density of 0.1 A·g-1,the energy density of 149.2 Wh·kg-1is achieved,and the maximum power density can reach up to 2195 W·kg-1.In addition,the capacity retention is 56%after 1000 cycles at 1 A·g^-1,achieving a significant improvement in cycle life compared with NCM111/LTO lithium-ion battery.NCM111/LTO+HC-type battery system will show great potential in the practical application of energy storage devices requiring rapid charging and discharging in the future.

参考文献

[1] Huang SF,Li ZP,Wang B,Zhang JJ,Peng ZQ,Qi RJ,Wang J,Zhao YF.N-doping and defective nanographitic domain coupled hard carbon nanoshells for high performance lithium/sodium storage.Adv Funct Mater.2018;28(10):1796294.

[2] Ge MY,Fang X,Rong JP,Zhou CW.Review of porous silicon preparation and its application for lithium-ion battery anodes.Nanotechnology.2013;24(42):422001.

[3] Zhang XH,Qiu XY,Kong DB,Zhou L,Li Z,Li XL,Zhi LJ.Silicene flowers:a dual stabilized silicon building block for high-performance lithium battery anodes.ACS Nano.2017;11(7):7476.

[4] Huang SF,Wang M,Jia P,Wang B,Zhang JJ,Zhao YF.N--graphene motivated SnO_2@SnS_2 heterostructure quantum dots for high performance lithium/sodium storage.Energy Storage Mater.2018.https://doi.org/10.1016/j.ensm.2018.11.024.

[5] Zheng HY,Qu QT,Zhu GB,Liu G,Battaglia VS,Zheng HH.Quantitative characterization of the surface evolution for LiNi_(0.5)Co_(0.2)Mn_(0.3)O_2/graphite cell during long-term cycling.ACS Appl Mater Interfaces.2017;9(14):12445.

[6] Jung SK,Gwon H,Hong J,Park KY,Seo DH,Kim H,Hyun J,Yang W,Kang K.Understanding the degradation mechanismsof LiNi_(0.5)Co_(0.2)Mn_(0.3)O_2 cathode material in lithium ion batteries.Adv Energy Mater.2014;4(1):1300787.

[7] Lou W,Gaumet JJ,Mai LQ.Antimonybased intermetallic compounds for lithiumion and sodiumion batteries:synthesis,construction and application.Rare Met.2017;36(5):321.

[8] Shi SS,Li ZP,Sun Y,Wang B,Liu QN,Hou YL,Huang SF,Huang JZ,Zhao YF.A covalent heterostructure of monodisperse Ni_2P immobilized on N,P-co-doped carbon nanosheets for high performance sodium/lithium storage.Nano Energy.2018;48:510.

[9] Li S,Yang Y,Xie M,Zhang Q.Synthesis and electrochemical performances of high-voltage LiNi_(0.5)Mn_(1.5)O_4 cathode materials prepared by hydroxide co-precipitation method.Rare Metals.2017;36(4):277.

[10] Yun FL,Tang L,Li WC,Jin WR,Pang J,Lu SG.Thermal behavior analysis of a pouch type Li[Ni_(0.7)Co_(0.15)Mn_(0.15)]O_2-based lithium-ion battery.Rare Metals.2016;35(4):309.

[11] Wu J,Lau WM,Geng DS.Recent progress in cobalt-based compounds as high-performance anode materials for lithium ion batteries.Rare Met.2017;36(5):307.

[12] Liang JJ,Wei ZX,Wang CY,Ma JM.Vacancy-induced sodium-ion storage in N-doped carbon nanofiber@MoS_2nanosheet arrays.Electrochim Acta.2018;285(20):301.

[13] Liu JD,Liang JJ,Wang CY,Ma JM.Electrospun CoSe@N--doped carbon nanofibers with highly capacitive Li storage.J Energy Chem.2018.https://doi.org/10.1016/j.jechem.2018.09.006.

[14] Huang J,Wei Z,Liao J,Ni W,Wang C,Ma JM.Molybdenum and tungsten chalcogenides for lithium/sodium-ion batteries:beyond MoS_2.J Energy Chem.2018.https://doi.org/10.1016/j.jechem.2018.09.001.

[15] Zuo WH,Li RZ,Zhou C,Li YY,Xia JL,Liu JP.Battery-supercapacitor hybrid devices:recent progress and future prospects.Adv Sci.2017;4(7):1600539.

[16] Simon P,Gogotsi Y,Dunn B.Where do batteries end and supercapacitors begin?Science.2014;343(6176):1210.

[17] Lukatskaya MR,Dunn B,Gogotsi Y.Multidimensional materials and device architectures for future hybrid energy storage.Nat Commun.2016;7:12647.

[18] Yao F,Pham DT,Lee YH.Carbon-based materials for lithium-ion batteries,electrochemical capacitors,and their hybrid devices.ChemSusChem.2015;8(14):2284.

[19] Karuppiah S,Franger S,Nallathamby K.Water-soluble green binder for Li_4Ti_5O_(12)anodes:effect of binder choice on lithium storage.ChemelEctroChem.2018;5(2):343.

[20] Gockeln M,Pokhrel S,Meierhofer F,Glenneberg J,Schowalter M,Rosenauer A,Fritsching U,Busse M,Madler L,Kun R.Fabrication and performance of Li_4Ti_5O_(12)/C Li-ion battery electrodes using combined double flame spray pyrolysis and pressure-based lamination technique.J Power Sour.2018;374:97.

[21] Sun LN,Xiong W,Mi HW,Li YL,Zhuo HT,Zhang QL,He CX,Liu JH.In situ coating of graphene-like sheets on Li_4Ti_5O_(12)particles for lithium-ion batteries.Electrochim Acta.2017;230:508.

[22] Ruan D,Huang Y,Li LY,Yuan J,Qiao Z.A Li_4Ti_5O_(12)+AC/LiMn_2O_4+AC hybrid battery capacitor with good cycle performance.J Alloys Compd.2017;695:1685.

[23] Hu XB,Deng ZH,Suo J,Pan Z.A high rate,high capacity and long life(LiMn_2O_4+AC)/Li4Ti_5O_(12)hybrid battery-supercapacitor.J Power Sour.2009;936(2):496.

[24] Hu XB,Deng ZH.Study on(LiMn_2O_4+AC)/Li_4Ti_5O_(12)hybrid battery-capacitor.J Chongqing Univ Technol.2012;26:21.

[25] Zhao JL,Wang JT,Chang ZH,Lu SG.Performance of Li-rich material with fluoroethylene carbonate as high-voltage electrolyte solvent.Chin J Rare Metals.2018;42(10):1077.

[26] Kasnatscheew J,Evertz M,Streipert B,Wagner R,Kl(o|")sch R,Vortmann B,Hahn H,Nowak S,Amereller M,Gentschev AC.The truth about the 1st cycle Coulombic efficiency of LiNi_(1/3)Co_(1/3)Mn_(1/3)O_2(NCM)cathodes.Phys Chem Chem Phys PCCP.2016;18(5):3956.

[27] Mukai K.Pseudo zero-strain insertion materials for Li-ion batteries:cross-sectional observations of LiNi_(1/2)Co_(1/2)O_2,LiNi_(1/3)Co_(1/3)Mn_(1/3)O_2,and LiNi_(0.8)Co_(0.15)Al_(0.05)O_2.Ionics.2018;24(8):1.

[28] Ghimbeu CM,Gorka J,Simone V,Simonin L,Martinet S,Vix-Guterl C.Insights on the Na~+ion storage mechanism in hard carbon:discrimination between the porosity,surface functional groups and defects.Nano Energy.2017;44:327.

[29] Li ZF,Bommier C,Chong ZS,Jian ZJ,Surta TW,Wang XF,Xing ZY,Neuefeind JC,Stickle WF,Dolgos M.Mechanism of Na-ion storage in hard carbon anodes revealed by heteroatom doping.Adv Energy Mater.2017;7(18):1602894.

[30] Gaddam RR,Yang DF,Narayan R,Raju K,Kumar NA,Zhao XS.Biomass derived carbon nanoparticle as anodes for high performance sodium and lithium ion batteries.Nano Energy.2016;26:346.

[31] Hu XB,Deng ZH,Suo J,Pan Z.A high rate,high capacity and long life(LiMn_2O_4+AC)/Li_4Ti_5O_(12)hybrid battery-supercapacitor.J Power Sour.2009;187(2):635.

[32] Ping LN,Zheng JM,Shi ZQ,Jie QI,Wang CY.Electrochemical performance of MCMB/(AC+LiFePO_4)lithium-ion capacitors.Sci Bull.2013;58(6):689.

[33] Sun XZ,Zhang X,Huang B,Zhang HT,Zhang DC,Ma YW.(LiNi_(0.5)Co_(0.2)Mn_(0.3)O_2+AC)/graphite hybrid energy storage device with high specific energy and high rate capability.J Power Sour.2013;243(6):361.