no 5 alkaline battery.Latest research progress on rational design of high-performance alkaline secondary battery electrode materials

In addition to the advantages of low cost, good safety, low toxicity, and environmental friendliness, alkaline secondary batteries (ARBs) also have the advantage of higher theoretical energy density than ARABs. In order to improve the electrochemical performance of alkaline energy storage systems, that is, the energy density, power density, cycle life, and high rate of the energy storage system

In addition to the advantages of low cost, good safety, low toxicity, and environmental friendliness, alkaline secondary batteries (ARBs) also have the advantage of higher theoretical energy density than ARABs. In order to improve the electrochemical performance of alkaline energy storage systems, that is, the energy density, power density, cycle life, high rate performance, etc. of the energy storage system, a large number of attempts have been made and new electrode materials suitable for alkaline batteries have been explored. Many reports have recognized that the electrochemical performance of these systems strongly depends on the intrinsic phase properties as well as structural and surface properties of the electrode materials. Prior to this, several researchers reviewed and summarized the work related to rechargeable alkaline energy storage systems. However, these reviews focus on various specific aspects of alkaline batteries, but there is no comprehensive and timely review and summary of the latest progress in alkaline rechargeable energy storage systems. Therefore, this article provides a comprehensive review and summary of the rational design of electrode materials and the latest progress in alkaline batteries. The article was published in the top international journal Adv.Func.Mater. The first author is Huang Meng.

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1. Alkaline battery chemistry principles and classification

1) Alkaline battery chemistry

Compared with ARABs, ARBs have higher energy density and power density and can fill the gap between lithium-ion batteries and supercapacitors (SCs). LIBs play a charge transfer role in the electrochemical behavior of lithium ion insertion/extraction and conversion in aqueous and non-aqueous electrolytes. In alkaline electrolytes, ARBs are mainly responsible for the H+ insertion/extraction and conversion mechanism that dominates the charge transfer between electrolytes. Although the same Faradaic reaction mechanism occurs in ARBs and pseudocapacitive SCs, both the surface and bulk electrode materials of the former participate in the reaction of alkaline batteries, which is similar to the reaction in LIBs, but pseudocapacitive SCs only involve the surface of the active material /near surface reaction. Reflected in cyclic voltammetry (CV) and galvanostatic charge and discharge, a strong Faradaic redox peak and an obvious voltage platform appeared in the electrochemical process of ARBs, which was different from the nearly rectangular curve and linear voltage curve of SCs.

2) Alkaline battery classification

Classified based on cathode materials, alkaline batteries mainly include manganese-based, nickel-based and cobalt-based alkaline batteries.

Manganese-based alkaline battery: Due to the low redox potential of manganese dioxide, this positive electrode is usually paired with a zinc negative electrode. Its working principle can be simplified as:

Positive electrode: MnO2+H2O+e-←→MnOOH+OH-, H+ insertion/extraction (4)

Negative electrode: Zn+4OH-←→[Zn(OH)4]2-+2e-, dissolution/precipitation process (5)

Full battery: 2MnO2+Zn+2H2O+2OH-←→[Zn(OH)4]2-+2MnOOH (6)

Nickel-based alkaline batteries: Nickel-based alkaline batteries include nickel-zinc, nickel-iron, nickel-cobalt, nickel-bismuth, nickel-cadmium and nickel-metal hydride batteries.

Nickel-zinc batteries have high energy/power density, high discharge voltage of ~1.75V, theoretical specific capacity of 372Whkg-1 and low cost. Nickel-based cathodes usually undergo the following electrochemical reactions:

NiOOH+H2O+e-←→Ni(OH)2+OH-, H+ insertion/extraction (8)

Therefore, the full reaction equation for nickel-zinc alkaline batteries is as follows:

2NiOH+Zn+2H2O+2OH-←→[Zn(OH)4]2-+2Ni(OH)2(9)

Cobalt-based alkaline battery: usually composed of Co3O4 positive electrode and zinc negative electrode. Based on the quality of Co3O4 positive electrode and zinc negative electrode, cobalt-zinc alkaline battery has a high energy density of 516Whkg-1 and an operating voltage of 1.78V. Co3O4 cathode can be converted into CoO2 through a two-step reaction:

Transformation: Co3O4+OH-+H2O←→3COOOH+e-(20)

H+ insertion/extraction: CoOOH+OH-←→CoO2+H2O+e-(21)

The full cell reaction can be described as follows:

2[Zn(OH)4]2-+CO3O4←→3CoO2+2Zn+2H2O+4OH-

2Cathode material design

2.1 Electrochemical control

2.1.1 Manganese-based cathode materials

Hertzberg et al. synthesized Bi2O3/β-MnO2 composite (MBDB) cathode material. When tested in a mixed KOH/LiOH (1:3) electrolyte, the material released a capacity of 360mAh/g because the formation of ZnMn2O4 was prevented, and Shows excellent cycling stability.

Figure 1.a) Reaction mechanism of MnO2 cathode material. b) Cycling performance of MBDB in 1MKOH+3MLiOH. c) In-situ EDXRD study of MBDB cycling in 1MKOH+3MLiOH electrolyte. d) Possible phase transition process of MBDB in 1MKOH+3MLiOH electrolyte.

In order to achieve the two-electron capacity of the MnO2 cathode, Yadav et al. designed a new Cu2+-embedded Bi-Binessite cathode. By inhibiting the electrochemical pathway to form Mn3O4, it released a theoretical capacity of 617mAh/g and performed > 6000 reversible cycles.

Figure 2. Galvanostatic charge and discharge curves of Bi-δ-MnO2 cathode without a) and b) Cu2+. c) Cycling performance diagram of Cu2+ embedded Bi-δ-MnO2 cathode material with different mass fractions of MnO2. d–f) Electrochemical reaction process during the regeneration process of Cu2+ embedded Bi-δ-MnO2 cathode material.

2.1.2 Nickel-based cathode materials

In order to obtain a high theoretical capacity of the α-Ni(OH)2/γ-Ni(OH)2 redox pair, in addition to ensuring the electrochemical pathway of this redox pair, the stability of α-Ni(OH)2 should also be considered to avoid side effects. Gong et al. reported a new NiCoAl-LDH and carbon nanotube (NiCoAl-LDH/CNT) composite cathode material for Ni-Zn alkaline batteries. Al and Co co-doped α-Ni(OH)2 cathode has a high capacity of 354mAh/g and good stability over 2000 cycles at 66.7A/g.

Figure 3.a) TEM image of NiAlCo-LDH/CNT. b) XRD patterns of NiAlCo-LDH/CNT, a-Ni(OH)2/CNT, NiAl-LDH/CNT and Ni(OH)2/CNT. c) CV curve at 40mV/s. d) Constant current discharge curve. e) Discharge capacity under different discharge current densities. f) Capacity cycle retention rate.

2.2 Structural design

Using Ni-NiO heterostructure nanosheets as the cathode can also solve the irreversibility problem of nickel-based cathodes. Scanning electron microscope and transmission electron microscope images show that the Ni-NiO-3 sample is composed of a NiO matrix and embedded metallic nickel nanoparticles, showing a rough and porous nanosheet morphology (Figure 4d). The four Ni-NiO heterostructure nanosheet samples, especially sample 3, showed a longer and flatter discharge plateau (Fig. 4f) than pure NiO (Fig. 4e) at different current densities. When the current density is 3.7A/g, the capacity of Ni-NiO-3 electrode material is as high as 5.78mAh/cm2, while the capacity of pure NiO electrode is 1.62mAh/cm2. After 10,000 cycles at a current density of 18.5 A/g, Ni-NiO-3 showed a capacity retention of 98.9% (Figure 4f).

Xu et al. designed a Co-doped Ni(OH)2 (CNH) cathode material grown on Ni nanowire array (NNA) (Figure 5c). At current densities from 5 to 10, 15 and 30A/g, the average discharge capacities of NNA@CNH electrode are 346, 304, 242 and 158 mAh/g, respectively, while those of NNA@Ni(OH)2 are respectively are 272, 189, 150 and 99mAh/g (Fig. 5d). At the maximum mass loading of 4 mg/cm2, the areal capacity of the NNA@CNH electrode increases almost linearly to approximately 1 mAh/cm2 (Fig. 5e). When evaluated for 5000 cycles at 30 A/g, NNA@CNH retained 90% of its capacity, showing superior cycle performance, while NNA@Ni(OH)2 only retained 62.1% of its capacity (Figure 5f). These three-dimensional structural designs provide more active sites and stable structures, achieving excellent cycleability and high reversibility of electrode materials.

Figure 4.d) SEM image of Ni–NiO-3 sample. e) Discharge curves of NiO and Ni–NiO-X electrode materials at a current density of 3.7A/g. f) Volumetric capacity of NiO and Ni–NiO-X electrode materials as a function of current density.

Figure 5.a) TEM image of SANF electrode material. b) Galvanostatic discharge curve of SANF electrode material. c) SEM image of NNA@CNH nanostructure, the inset is the TEM image. d) Rate performance diagram of NNA@CNH-1 and NNA@Ni(OH)2 electrode materials. e) Changes in mass and area capacity of NNA@CNH-1 electrode material with mass loading. f) Cycling performance test of NNA@CNH-1 and NNA@Ni(OH)2 electrode materials.

Recently, our research group reported a dendritic Co(CO3)0.5(OH)x·0.11H2O@CoMoO4 (CC-CCH@CMO) cathode material grown on carbon cloth (Figure 6a). The CV curve of CC-CCH@CMO cathode material has two pairs of redox peaks, showing a complete reduction peak even at 50 mV/s (Figure 6b). At a current density of 1mA/cm2 (0.36A/g), the electrode can release an areal capacity of 0.72mAh/cm2 (260.2mAh/g) (Fig. 6c), and even at a current density of 64mA/cm2 (Fig. 6d ), it also has a high capacity retention rate of 67.6%.

Figure 6. a) HRTEM image of CC–CCH@CMO. b) CV and c) charge-discharge curves of CC–CCH@CMO. d) Areal capacity of CC–CCH@CMO under different current densities. e) HRTEM image of NiCo2S4@NiCo2S4 heterogeneous nanostructure. f) Capacity comparison of NiCo2S4@NiCo2S4, NiCo2O4@NiCo2O4 heterogeneous nanostructures and NiCo2O4 nanorod arrays under unacceptable current density. g) Schematic diagram of electron and ion transport in porous NiCo2S4@NiCo2S4 nanostructure. h) Cycling performance and Coulombic efficiency diagram of NiCo2O4@NiCo2O4 heterogeneous nanostructure at a current density of 60mA/cm2. The inset is the charge-discharge curve after 10,000 cycles.

2.3 Surface modification

In a new research report, Zeng et al. simultaneously introduced oxygen vacancies and phosphate ions to improve the capacity and rate performance of NiCo2O4 cathode materials. The low-temperature electron paramagnetic resonance test of P-NiCo2O4-x after phosphating treatment showed a strong signal peak with a g value of 2.27, proving the generation of Co2+ (Figure 7a). The introduced oxygen vacancies and surface phosphate ions play an important role in improving the surface activity and reaction kinetics of NiCo2O4. The P-NiCo2O4-x electrode also has high cycling stability over 3000 cycles (Fig. 7f).

Figure 7.a) Low temperature electron paramagnetic resonance spectra of NiCo2O4 and P–NiCo2O4-x. b) XPS pattern of O1s. c) Nyquist plot of NiCo2O4 and P–NiCo2O4-x electrode materials. d) Specific capacity of P–NiCo2O4-x-X electrode material at different current densities. e) 3000 cycle performance of NiCo2O4 and P–NiCo2O4-x electrode materials.

3Anode material design

3.1 Negative electrode based on conversion mechanism

3.1.1 Iron-based materials

Recently, Guo et al. proposed an anode material utilizing ultra-small iron oxide nanocrystals (mc-FeOx/C) wrapped in graphitic carbon. The as-prepared mc-FeOx/C showed a high capacity of 370.2 mAh/g at 2 A/g, maintaining 93.5% after 1000 cycles (Fig. 8b), as well as good rate performance and energy density (Fig. 8c). In comparison, the capacity retention rate of traditional FeOx/C composites is only 61.2%. In another work, in order to fully utilize the theoretical capacity, a strongly coupled nanoiron/carbon nanotube anode material was designed. Since fast and efficient electron transport is ensured, its discharge capacity is 800mAh/g at a current density of 200mA/g. However, due to the dissolution/re-precipitation of the active material, the capacity dropped to 423 mAh/g after 100 cycles (Figure 8d). The stability of this material can be enhanced by additives and increasing the discharge cut-off voltage, but this change leads to a reduction in discharge capacity, but ensures that the electrode is stable for 3500 cycles, with an average Coulombic efficiency of more than 97 at 1C rate and 100% DOD. % (Fig. 8e).

Figure 8. a) HRTEM image of mc-FeOx/C. b) Cycling stability test of mc-FeOx/C. c) Capacity-current density diagram under different current densities. d) Discharge curve of Fe/MWCNT nanocomposite. e) Cyclic testing of sintered iron electrode materials at 1C and 100% DOD.

3.1.2 Bismuth-based materials

In order to better solve the cycling problem of bismuth-based anodes and improve electrochemical performance, Zeng et al. adopted a structural design strategy followed by annealing at a temperature of 200°C to synthesize a three-dimensional layered Bi200 nanostructure (Fig. 9a). The specific capacity of Bi200 electrode material is as high as 96.2mAh/g at 4.5A/g, and the capacity at 45A/g remains at 90.5mAh/g (Figure 9c); after 10,000 cycles at 30A/g, the capacity decays less than 4% (Fig. 9d).

Figure 9. SEM image of Bi200 sample. b) TEM image of Bi200 sample. c) Discharge curve of Bi200 sample. d) 10,000 cycle performance of untreated Bi and Bi200 electrode materials at a current density of 30A/g and the capacity retention rate of three different Bi200 electrode materials before and after cycles. e) SEM and f) HRTEM images of P–Bi–C electrode material. g) Area capacity and capacity retention rate of Bi–C and P–Bi–C electrode materials under different current densities.

Combined with three-dimensional structural design, the introduction of holes can achieve higher capacity and energy density of electrode materials. Recently, Zeng et al. synthesized a 3D porous Bi nanoparticle