Fabrication of NaNiF3/Ni composite and its application in lithiumion batteries

Shibing Ni, Jianjun Ma, Xiaohu Lv, Xuelin Yang n, Lulu ZhangCollege of Materials and Chemical Engineering, Collaborative Innovation Center for Energy Equipment of Three Gorges Region, Three Gorges University,8 Daxue Road, Yichang, Hubei 443002, China

a r t i c l e i n f o

Article history:Received 1 February 2014Accepted 11 March 2014Available online 19 March 2014

Keywords:Crystal structureComposite materialSodium nickel fluorideLithium ion battery

a b s t r a c t

NaNiF3/Ni composite material is successfully synthesized by a novel electrochemical corrosion method.The morphology and size of the as-prepared composite material are studied by field emission scanningelectron microscopy (FE-SEM). The results indicate that the NaNiF3 shows particle-like morphology withmean size about 3 μm, which grows directly on the surface of Ni foam. Electrochemical properties of theNaNiF3/Ni as anode for lithium ion batteries are studied by conventional charge/discharge test, whichshow obvious voltage plateaus in charge/discharge curves, endowing it with potential application inlithium ion battery.

& 2014 Elsevier B.V. All rights reserved.

1. Introduction

Composite materials have always played an important role inthe development of lithium ion batteries. For example, thediscovery of LiCoO2 and its application as cathode material forlithium ion battery has promoted the development of lithium ionbattery, which has become the main cathode material for a longperiod of time [1]. As another kind of cathode material, LiFePO4

shows attractive electrochemical performance, which has beenintensively studied [2]. Li4Ti5O12 shows good electrochemicalperformance as anode for lithium ion battery [3], which has beengradually used in commercial lithium ion battery. Thus exploringnew kinds of composite material and studying their application inlithium ion battery are of great interest. In addition, as known, theelectrode material usually shows improved electronic conductivityand structure stability when directly growing them on conductivemetal substrate, which is beneficial to their application in lithiumion battery [4–8]. However, report on the preparation of compositematerials that directly grow on metal substrate is rarely seen, andsays nothing about the application of such composite material inlithium ion batteries.

Here in this paper, we report the preparation of NaNiF3/Ni via afacile electrochemical corrosion method. The application of the as-prepared NaNiF3/Ni as anode for lithium ion battery was firstlystudied by conventional charge/discharge test, which showsobvious charge/discharge plateaus, endowing it with potential

application in lithium ion battery. The fabrication method isnew, and this is the first report on the application of NaNiF3/Niin lithium ion battery to the best of our knowledge.

2. Experimental

The chemicals were of analytical grade and purchased fromShanghai Chemical Reagents. In a typical process, 0.25 g NaF wasdissolved in 30 ml distilled water, then 0.6 ml H2O2 and 0.3 ml HClwere added into the solution. After stirring for 20 min, theobtained homogeneous solution was transferred into a 50 mlteflonlined autoclave, Ni foams (100 PPI pore size, 380 g m�2

surface density, 1.5 mm thick, purchased from Changsha LyrunNew Material) were then placed in the autoclave, distilled waterwas subsequently added to 80% of its capacity. The autoclave wasthen sealed and placed in an oven, heated at 160 1C for 24 h. Theweight of active NaNiF3 on Ni can be estimated by washing theNaNiF3/Ni electrode in diluted HCl.

The structure and morphology of the resulting products werecharacterized by X-Ray powder diffraction (Rigaku Ultima IV Cu Kαradiation λ¼1.5406 Å) and field-emission scanning electronmicroscopy (FE-SEM JSM 7500F, JEOL).

For the fabrication of Li-ion battery, NaNiF3/Ni disc electrodeswith diameter of 14 mm were dried at 120 1C for 24 h in vacuumoven. Coin-type cells (2025) of Li/1 M LiPF6 in ethylene carbo-nate, dimethyl carbonate and diethyl carbonate (EC/DMC/DEC,1:1:1 v/v/v)/NaNiF3/Ni were assembled in an argon-filled drybox (MIKROUNA, Super 1220/750, H2Oo1.0 ppm, O2o1.0 ppm).A Celgard 2400 microporous polypropylene was used as the

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Materials Letters

http://dx.doi.org/10.1016/j.matlet.2014.03.0570167-577X/& 2014 Elsevier B.V. All rights reserved.

n Corresponding authors. Fax: þ86 717 6397559.E-mail addresses: shibingni07@gmail.com (S. Ni), xlyang@ctgu.edu.cn (X. Yang).

Materials Letters 124 (2014) 264–266

separator membrane. The cells were tested in the voltage rangebetween 0.02 and 3 V with a multichannel battery test system(LAND CT2001A). The cyclic voltammetry (CV) measurement ofthe electrodes was carried out on a CHI660C electrochemicalworkstation at a scan rate of 0.2 mV s�1 between 0.02 and 3 V.

3. Results and discussion

Typical XRD pattern of the sample is shown in Fig. 1. As seen,three typical diffraction peaks located at 44.41, 51.71 and 76.41(marked by �) correspond to Ni (111), (200) and (220) faces,respectively (JCPDS no. 04-0850). The diffraction peaks located at23.01, 32.31, 32.81, 33.31, 38.91, 47.21, 53.21and 59.31(marked by n)can be attributed to the crystallographic planes of NaNiF3, which isin agreement with JCPDS no. 10-0158. The formation of NaNiF3/Nican be understood as an electrochemical corrosion, and theelectrochemical reactions are likely to be as follows:

Ni/Ni-Ni2þ/Niþ2e� (1)

HCl-HþþCl� (2)

2H2O2þ4H�þ4e�-4H2O (3)

NaF-NaþþF� (4)

Ni2þ/Niþ3F�þNaþ-NaNiF3/Ni (5)

Fig. 2(a) is a low magnification SEM image of the obtainedNaNiF3/Ni electrode. As seen, a large number of micro-particles on

the surface of the electrode can be observed, which are muchdifferent from that of Ni foam with the same magnification ( insetof Fig. 2(a)), suggesting the successful growth of NaNiF3 on Nifoam. High magnification SEM image of the NaNiF3/Ni is shown inFig. 2(b), which suggests that these micro-particles are of meansize about 4 μm. Some of these nanoparticles show coarous sur-face, consisting of a large number of particles with little size.

Fig. 3(a) shows the initial three charge/discharge curves of theNaNiF3/Ni at a current density of 0.1 mA cm�2. As seen, the initialdischarge curve differs much from the subsequent two, showingthree sloping potential regions (1.36–1.08, 1.08–0.62 and 0.62–0.02 V),whereas the sloping potential regions for the 2nd and 3rd dischargecurves locate at 2.0–1.0, 1.0–0.56 and 0.56–0.02 V, respectively. Thedifference may be caused by irreversible lithium ions consumptiondue to the formation of solid electrolyte interface (SEI) in the initialdischarge process, which is similar to that of metal oxides [5,8,9].The initial three charge curves show similar profile, exhibiting threesloping potential regions located at 0.1–1.0, 1.0–2.2 and 2.2–3.0 V,respectively. As shown in the inset of Fig. 3(a), the 1st cathodic scanshows two reduction peaks located at 0.6 and 0.93 V, which can beascribed to the reduction of NaNiF3 into Ni and the formationof solid electrolyte interface (SEI). The reduction peaks shift to0.7 and 1.4 V in the 2nd cathodic scan, which can be ascribed to theactivation of NaNiF3. The initial two anodic curves show similarprofile with three oxidation peaks located at 1.09, 1.76 and 2.39 V,which can be ascribed to the oxidation of Ni into NaNiF3 andpartial decomposition of SEI. The CV curves consist well withthe charge and discharge curves. The cycle performance of theNaNiF3/Ni is shown in Fig. 3(b), which exhibits initial dischargeand charge capacity of 0.38 and 0.26 mAh cm�2 (0.7 mg), respec-tively. The extra capacity in the initial discharge curve may berelevant to the formation of SEI and the high surface area of the Nifoam, which is similar to that of Cu2O–Cu [10]. The discharge andcharge capacities decrease along with cycle number and thengradually arrive at stable values, maintaining of 0.12 mAh cm�2

after 100 cycles.Fig. 4(a) is a low magnification SEM image of the NaNiF3/Ni

electrode after 100 cycles. Uniform film-like morphology can beobserved, uponwhich a little amount of micro-particles locate. Thesurface morphology of the cycled electrode differs much from thatof the NaNiF3/Ni and Ni foam, which suggests the NaNiF3/Nielectrode undergoes phase transition during the charge/dischargeprocess, being similar to transition metal oxides that possess redoxreaction mechanism [4,6,11]. High magnification SEM image of thecycled electrode is shown in Fig. 4(b), which indicates that the filmis of smooth surface and these micro-particles are of pliable edgesand corners with mean size of about 2 μm. The special morpho-logical characteristic of the cycled electrode is similar to that ofFig. 1. XRD pattern of the as-synthesized sample.

Fig. 2. SEM images of the NaNiF3/Ni electrode with low (a) and high (b) magnification. The inset of (a) is a SEM image of Ni foam.

S. Ni et al. / Materials Letters 124 (2014) 264–266 265

NiO/Ni electrode [6], which was proposed to be relevant toelectrochemical activation and electrochemical sintering [11].

4. Conclusions

In conclusion, NaNiF3/Ni composite was successfully preparedvia the novel electrochemical corrosion method. The electroche-mical performance of the as-prepared NaNiF3/Ni composite asanode for lithium ion battery was studied by conventional charge/discharge test, which exhibits obvious voltage plateaus, endowingNaNiF3 with potential applications in lithium ion batteries. As themorphology and size have important effects on the physical andchemical properties of materials, promising work should be doneon tuning the morphology and size, and optimizing the electro-chemical performance of NaNiF3. In addition, the fabricationmethod reported in this research work may have an importantimplication on the preparation of other composite material viain situ technology.

Acknowledgments

We gratefully acknowledge the financial support from NationalNatural Science Foundation of China (NSFC, 51272128, 51302152and 51302153). Moreover, the authors are grateful to Dr. Jianlin Liat Three Gorges University for his kind support to our research.

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Fig. 3. The initial three charge/discharge curves (a) and cycle performance (b) of the NaNiF3/Ni. The inset of (a) is the initial two CV curves of the NaNiF3/Ni.

Fig. 4. SEM images of the cycled NaNiF3/Ni electrode with low (a) and high (b) magnification.

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