Elsevier

Electrochimica Acta

Volume 85, 15 December 2012, Pages 554-559
Electrochimica Acta

Effects of calcium lignosulfonate on the performance of zinc–nickel battery

https://doi.org/10.1016/j.electacta.2012.08.111Get rights and content

Abstract

As a cathodic corrosion inhibitor and surfactant additive, the effects of calcium lignosulfonate (CLS) on the electrochemical behaviors of ZnO electrode were examined by polarization measurements, EIS (electrochemical impedance spectrum) and CV (cyclic voltammogram) electrochemical technique methods. Both of the corrosion current density and anodic Tafel slope for the ZnO with CLS additive (CZO) anode are smaller than those for the ordinary ZnO (OZO) anode, which indicates that the CLS has a good anticorrosion effect. Compared the CZO anode with the OZO anode, negative shift of the corrosion potential means CZO anode has a higher overpotential of hydrogen evolution. In order to explore the electrochemical corrosion performances of the zinc anodic process, further more studies such as morphological analysis, galvanostatic charge–discharge tests are also applied.

Introduction

There is a wide variety of applications for metal zinc as a high capacity anodic material in the secondary alkaline batteries due to its low equilibrium potential, low cost and non-toxicity [1]. The sealed Zn–Ni battery has many advantages including good specific energy, high open-circuit voltage, abundant raw materials and environmental friendliness. Nevertheless, the widespread industrialization of sealed Zn–Ni batteries has been prevented by series of problems existing in zinc electrode. One of the major problems is the poor and unstable cycling capability. During the charge/discharge cycles, the electrochemical dissolution and deposition of zinc proceeds irregularly at the electrode surface resulting in shape change, dendritic formation and passivation [2]. Simultaneously, owing to the high reactivity of the zinc anode, the zinc anode exist severe self-corrosion in the aqueous alkaline solution. Its corrosion and conjugate equation are as follows:Zn + 4OH = Zn(OH)42− + 2e2H2O + 2e  H + 2OH

The flocculent Zn(OH)2 will gradually deposit on the surface of electrode, when the concentration of Zn(OH)42− in the vicinity of the interface reaches saturated level as the dissolution of discharging products.Zn(OH)42− = Zn(OH)2 + 2OH

When the entire surface of the electrode is covered with the enhanced Zn(OH)2 passive film, the effective reaction area of the zinc anode will shrink result in rapidly increasing of the corrosion current density and polarization of zinc anode. Many attempts have been made to improve zinc utilization, which would be classified into several aspects as follows:

  • (1)

    Hydroxide like Ca(OH)2Ca(OH)2 + 2ZnO + 2H2O = Ca[Zn(OH)3]2

    The insoluble calcium zincate leads to less shape change, less dendrite growth and higher discharge capacity and longer cycle life [3], [4], [5].

  • (2)

    Metal oxide like BaO [6], which can decrease the solubility of discharge product in the alkaline electrolyte. Bi2O3 [7], [8], SnO2 [9], V2O5 [10], PbO [11], which can be reduced to form dense settled layer with zinc through co-deposition.

  • (3)

    Surfactants [12], [13], [14] as well as some other dispersants [15], which could influence the active material dissolution loss and passivation of the zinc electrode.

Calcium lignosulfonate (CLS) is a by-product of the pulp and paper industry, which is a highly cross-linked polymer composed of different phenyl-propanoid units and synapyl alcohols. Apart from the hydrophobic C6–C3 structures, there are a considerable number of anionic groups including sulfonic and carboxylic acids as well as alkyl and phenolic hydroxyl groups [16]. Therefore, lignosulfonate (LS) can act as a surfactant which exhibits the property of wettability, adsorptivity and dispersibility, is widely used as a dispersing agent in the fields of dye, paint petroleum as well as construction industry. The same hydrophilic group (single bondSO3H) of CLS like 1,3,5-phenyl-3-sulfonic acid potassium (KPTS) and sodium dodecyl benzene sulfonate (SDBS) together with alkyl and phenolic hydroxyl groups may have great influence on the physicochemical properties of its surface. Doddapaneni [17] reported that the 1,3,5-phenyl-3-sulfonic acid potassium (KPTS) added into the electrolyte could obtain beneficial effect on the electrochemical performance of zinc anode. Yang [18] also had studied the additive of 2 wt% sodium dodecyl benzene sulfonate (SDBS) into the electrolyte which can increase the zinc capacity utilization up by 35% and decrease the zinc electrode's passivation effectively.

Moreover, the Ca2+ of the CLS can react with the zincate in the alkaline electrolyte, the reaction equation as follow:Ca2+ + 2OH + 2ZnO + 2H2O = Ca[Zn(OH)3]2

Therefore, CLS has a similar effect like Ca(OH)2, which can reduce the active materials dissolution in the electrolyte, minimize shape change and dendrite of zinc anode. In this paper, an attempt of adding the anionic-surfactant CLS into ZnO has been made to explore the influence on the electrochemical performance of nickel–zinc battery and evaluate the effects of CLS on respect of surface activity, dispersion and anticorrosion.

Section snippets

The preparation of zinc electrode

The pasted CZO electrodes were prepared from an aqueous slurry, containing 85 wt% ZnO, 4 wt% PTFE (60 wt% diluted emulsion), 3 wt% graphite and 8 wt% CLS, the 2 cm × 2 cm copper mesh was used as the current collector substrate. The electrodes were dried at room temperature for 24 h and pressed at the pressure of 30 MPa to a thickness of 0.35 mm. Similarly, the OZO electrode for comparison was prepared by the same method. A pasted nickel hydroxide (β-Ni(OH)2) electrode served as the positive electrode. The

Effects of CLS additive on the discharge capacity of the zinc anode

The capacity rate for the Ni(OH)2 cathode and zinc anode is 3:1, so the capacity of Zn/Ni cells is determined uniquely by the zinc anode. Fig. 1 presents the variation of the discharge capacity with the number of cycles for OZO and CZO anode. The discharge capacity declines as the number of cycles increases. During the first 10 cycles, the discharge capacity of OZO anode is higher than the CZO anode. But after 20 cycles, the discharge capacity of OZO anode decreases rapidly throughout the

Conclusions

The ZnO added with 8 wt% CLS shows the high discharge capacity and utilization ratio of active material, excellent cycling stability, and good electrochemical properties. The reason is the additive of CLS can prevent the charging products from contacting with the strong alkaline electrolyte directly and reduce the discharge rate and self-corrosion of zinc anode. The negative shift of corrosion potential shows that the additive of CLS can increase the hydrogen evolution overpotential, retarding

Acknowledgments

We thank the National Natural Science Foundation of China (No. 91023031), Innovation Fund for Technology Based Firms of China in 2010 (No. 10C26214104497) and Production, Teaching and Research Integrated Project of Guangdong Province and Ministry of Education (No. 2010B090400341) for their financial support.

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