4.3 Composite ZnO-graphene materials

4.2 Substrate growth

Zinc Oxide Based Nano Materials and Devices

sheets up to a single layer [54].

phenomena occur in different regions of a reactor [66].

graphene, with a mismatch in network parameters of 1.3 % [54, 64].

of graphene and have proposed an anode in Li-ion batteries.

Figure 7.

124

ZnO-rG obtained after a thermal treatment at 600 °C.

The CVD process, as previously described, is a relatively complex process because of the equipment necessary to carry out the synthesis, but it allows obtaining graphene of higher quality at low cost, with larger sizes and more complex forms than the exfoliation processes of graphite [54, 57, 65, 66]. The team of Kim et al. [67] was among the first to report obtaining graphene by the CVD method on a Ni substrate, proving that the monolayers obtained were of much better quality than those of exfoliation. Since then, several authors have continued research to improve the technique, either by lowering the synthesis temperature as reported by Jang et al. [68], who obtained graphene at temperatures between 100 and 300 °C deposited on copper sheets, using benzene. Other authors such as Sagar et al. [58] have synthesized highly porous structures based on interconnected sheets

Scheme of obtaining the MC type ZnO-rG. Left: material of the precursor phase Zn(OH)2-GO. Right: the MC

This is a totally different way to the previous methods since the graphene sheets

The chemical vapor deposition method is perhaps one of the most promising and relatively low-cost techniques to obtain good quality graphene. Broadly speaking, the technique consists in the deposition of a solid film on a substrate, where the chemical species of the material deposited come from species in vapor phase and are deposited through chemical reactions. In an ideal CVD process, the transport kinetics of gases is often complicated and complex, since convection and diffusion

The process for obtaining graphene by CVD can be divided into two stages: the first is the pyrolysis of the carbon precursor and the second the formation of the graphene structure. In an ideal synthesis to obtain graphene, temperatures of up to 2500 °C would be needed to overcome the energy barrier that allows the reaction on the surface of the substrate; for this reason, catalysts are used, which are mostly elemental metals, which contribute to the pyrolization of carbon precursors. One of the most used substrates is Ni (111) since it has a structure very similar to that of

can be grown directly on a surface. And the size of the sheets does not depend directly on the size of a graphite crystal, as in the exfoliation methods. Growth can occur in two ways: whether the carbon exists on the surface of the substrate or it is added by chemical vapor deposition (CVD). Graphene can be obtained simply by heating and cooling a silicon carbide crystal, under suitable conditions, obtaining

An CM of ZnO-graphene (ZnO-G) could have a large number of assembly structures, however, can be considered six principally, the most used in this type of CM for Li-ion batteries: (a) anchored, (b) wrapped, (c) encapsulated, (d) type sandwich, (e) laminar, and (f) mixed. In all cases, graphene, being a twodimensional material, is the one that functions as a support for dispersed nanoparticles whose three-dimensional morphology can vary in different sizes, shapes, and crystallinity [13, 66].

Currently, the CM based on ZnO and carbon are very diverse and with variations in the morphology of both phases of the components. Figure 7 shows the obtaining of an CM of possible interest with the specific case of obtaining the dispersed phase of the phases of the ZnO with a Wurtzite type crystal structure, whose structure is more stable to standard conditions; this phase is the most attractive for, it is mainly used in CM for Li-ion batteries, also presented with a wide variety of morphologies; while for graphene, it usually presents different characteristics and properties according to its synthesis method [25, 69].

In recent years, a great amount of research has been carried out regarding the morphology of ZnO, since most of these works seek to increase the area, modifying the morphology and thus increasing the electrochemical properties, for its application in Li-ion batteries [16]. The investigations that have been carried out regarding the control of the crystallinity in the particles of the ZnO, to increase the capacity, are very few. Recently Mei et al. [17] published a paper in which they analyzed the degree of crystallinity and structural patterns of ZnO as an anode in Li-ion batteries. In this work, they used the hydrothermal synthesis in which they modified concentrations, to obtain different morphologies and then carried out treatments at different temperatures, this to control the degree of crystallinity. Finally, Mei et al. concluded that morphology was an important part in the capacity, since certain morphologies present a greater quantity of internal spaces, which help to compensate the volumetric changes; however, the samples whose crystallinity was controlled presented a specific capacity of 1328 mAhg<sup>1</sup> in the first cycle and 663 mAhg<sup>1</sup> at 50 cycles. In this work, it is worth mentioning that the particles obtained are of the micrometric order, contrary to what is generally reported with nanometric materials, such as Li et al. [18] that dispersed ZnO nanoparticles in


### Table 2.

Electrochemical characteristics of ZnO applied as an anode material in Li-ion batteries.

graphene, obtaining an initial capacity of 1652 mAhg<sup>1</sup> , but the retention capacity decreased to 318 mAhg<sup>1</sup> .

and graphene, of which graphene, in this case, is reduced with nitrogen and showed

The high area and the conductivity properties of graphene are the main properties that call attention to this material to be used as an anode in Li-ion batteries. The first reported evidence of Li storage on a large scale was 500 mAhg<sup>1</sup> for the first cycle and 300 mAhg<sup>1</sup> at just 20 cycles; currently values of up to 3000 mAhg<sup>1</sup> have been reported for the first cycle and decrements to values of 200 mAhg<sup>1</sup> after a few cycles [64]. Table 3 shows some data of the reported GO properties by different reduction methods. It should be mentioned that the GO of the data in

When analyzing the data in Table 4, it is observed that the efficiency or loss of capacity in graphene is notoriously greater due to the formation of the SEI; furthermore, it is observed that the GO reduced by thermal treatments, under an argon atmosphere, it has the best reversible capabilities and a greater number of cycles. The recently published ZnO-rG CMs are based on a reduced GO afterward and in which the ZnO nanoparticles are deposited or grow in situ in the leaves. In Table 4, some relevant values of CM of ZnO-rG are shown, in which the ZnO particles are of the order of hemispherical nanoparticles. Now, by comparing the values of the reversible capacity, it can be seen that they are close to 500 mAhg<sup>1</sup> on an average of per 100 cycles. The data reported in the literature for ZnO-G composites have very low efficiencies of around 50 %, however, some reports such as that of Dai et al. [50], Eliana et al. [25], and Shen et al. [43] have reported values very close to

The efficiency problems that currently arise in the materials for Li-ion battery anodes are mainly due to the pulverization and fragmentation of the said materials, caused by the volumetric changes and stability problems during the charge/discharge cycles. On the other hand, one of the factors that remain unfinished for this type of CMs is the surface interaction between graphene and MO that during the charge and discharge cycles is affected by parasitic reactions that impede the sta-

The evidences reported in the scientific literature show an open thematic for the design of composite materials with the intention of directly impacting on this time of tool for the storage of electrochemical energy, being the ZnO-graphene system a

The authors are grateful for the support granted in the Call 2019 issued by the Program of Support for Scientific and Technological Research in the Educational Programs of the Federal, Decentralized Technological Institutes and Centers belonging to the National Technological of Mexico (TecNM) for the support assigned to the Project (5269.19-P); and to the Higher Technological Institute of Irapuato (ITESI) for the allocation of support from its Institutional Program for the

a very remarkable reversible capacity, comparing it with other results. The graphene used in most CMs is obtained by chemical exfoliation, called GO, which has a number of advantages with pristine-type graphene. The GO can be obtained in large quantities and of sufficient quality, using the modified Hummers method, to be used in CM in a large number of applications, as in Li-ion batteries [5, 54].

Table 3 was obtained by the modified Hummers method.

Anodic ZnO-Graphene Composite Materials in Lithium Batteries

DOI: http://dx.doi.org/10.5772/intechopen.86169

bility and diffusion of charges between both materials [13, 66].

great candidate to be used as a constituent material of the anode.

Strengthening of Academic Staff (PIFOCA/PIFOPA/PIICYT 2019).

the theoretical capacity.

5. Conclusions

Acknowledgements

127

Table 2 shows the data reported in the literature for the comparison of the reversible capacity and the number of cycles of the different morphologies of ZnO as an anode in Li-ion batteries. It is possible to identify the effect of each morphology in the particle of the ZnO; the geometry of the bars is distinguished from the others, because it presents a greater reversible capacity, which suggests a greater stability in the processes of lithiation and sliding. In Table 2, it can be seen that some reversible capacity values greater or closer to 600 mAhg<sup>1</sup> , the ZnO particles are CM shaped with a carbonaceous material. However, the value of 663 mAhg<sup>1</sup> of the microbars reported by Mei et al. It is of great interest, because in spite of not being of nanometric size and not being like CM it has a great reversible capacity.

The ZnO-rG CMs promise better results due to the good properties of graphene. Table 2 shows results of some CMs of ZnO with carbon, porous carbon, graphite,


### Table 3.

Electrochemical characteristics of graphene in Li-ion batteries.


### Table 4.

Electrochemical characteristics of an CM of ZnO-G in Li-ion batteries.

### Anodic ZnO-Graphene Composite Materials in Lithium Batteries DOI: http://dx.doi.org/10.5772/intechopen.86169

and graphene, of which graphene, in this case, is reduced with nitrogen and showed a very remarkable reversible capacity, comparing it with other results. The graphene used in most CMs is obtained by chemical exfoliation, called GO, which has a number of advantages with pristine-type graphene. The GO can be obtained in large quantities and of sufficient quality, using the modified Hummers method, to be used in CM in a large number of applications, as in Li-ion batteries [5, 54].

The high area and the conductivity properties of graphene are the main properties that call attention to this material to be used as an anode in Li-ion batteries. The first reported evidence of Li storage on a large scale was 500 mAhg<sup>1</sup> for the first cycle and 300 mAhg<sup>1</sup> at just 20 cycles; currently values of up to 3000 mAhg<sup>1</sup> have been reported for the first cycle and decrements to values of 200 mAhg<sup>1</sup> after a few cycles [64]. Table 3 shows some data of the reported GO properties by different reduction methods. It should be mentioned that the GO of the data in Table 3 was obtained by the modified Hummers method.

When analyzing the data in Table 4, it is observed that the efficiency or loss of capacity in graphene is notoriously greater due to the formation of the SEI; furthermore, it is observed that the GO reduced by thermal treatments, under an argon atmosphere, it has the best reversible capabilities and a greater number of cycles. The recently published ZnO-rG CMs are based on a reduced GO afterward and in which the ZnO nanoparticles are deposited or grow in situ in the leaves. In Table 4, some relevant values of CM of ZnO-rG are shown, in which the ZnO particles are of the order of hemispherical nanoparticles. Now, by comparing the values of the reversible capacity, it can be seen that they are close to 500 mAhg<sup>1</sup> on an average of per 100 cycles. The data reported in the literature for ZnO-G composites have very low efficiencies of around 50 %, however, some reports such as that of Dai et al. [50], Eliana et al. [25], and Shen et al. [43] have reported values very close to the theoretical capacity.

The efficiency problems that currently arise in the materials for Li-ion battery anodes are mainly due to the pulverization and fragmentation of the said materials, caused by the volumetric changes and stability problems during the charge/discharge cycles. On the other hand, one of the factors that remain unfinished for this type of CMs is the surface interaction between graphene and MO that during the charge and discharge cycles is affected by parasitic reactions that impede the stability and diffusion of charges between both materials [13, 66].

### 5. Conclusions

graphene, obtaining an initial capacity of 1652 mAhg<sup>1</sup>

some reversible capacity values greater or closer to 600 mAhg<sup>1</sup>

Table 2 shows the data reported in the literature for the comparison of the reversible capacity and the number of cycles of the different morphologies of ZnO as an anode in Li-ion batteries. It is possible to identify the effect of each morphology in the particle of the ZnO; the geometry of the bars is distinguished from the others, because it presents a greater reversible capacity, which suggests a greater stability in the processes of lithiation and sliding. In Table 2, it can be seen that

are CM shaped with a carbonaceous material. However, the value of 663 mAhg<sup>1</sup> of the microbars reported by Mei et al. It is of great interest, because in spite of not being of nanometric size and not being like CM it has a great reversible capacity. The ZnO-rG CMs promise better results due to the good properties of graphene. Table 2 shows results of some CMs of ZnO with carbon, porous carbon, graphite,

Rapid exfoliation at 1050 °C/N2 2000 1200 5 [64] Exfoliation 300 °C/Ar 2100 600 100 [64]

Fast exfoliation at 1050 °C/Ar 2035 848 40 [5] Exfoliation at 300 °C/Ar 2137 478 100 [65] Thermal reduction exfoliation 1480 500 60 [74] Thermal reduction exfoliation/N2 3250 1354 50 [75]

ZnO/G 516 100 [35] ZnO/GN 1100 100 [50] AZO/G 391 100 [49] ZnO/G 360 200 [76] ZnO/G 550 100 [77] ZnO/G 560 100 [78] ZnO/G 300 50 [79] ZnO/CN 1047 100 [80] ZnO/G 749 100 [81] ZnO/G 550 100 [82] Cu/ZnO/G 630 100 [83] ZnO/C 520 100 [84] ZnO/CN 1177 100 [85] ZnO/NSG 720 100 [73]

NC = nitrided carbon; G = graphene; NG = nitrided graphene; NSG = nitrided-sulfurized graphene.

Electrochemical characteristics of an CM of ZnO-G in Li-ion batteries.

Reversible capacity (mAhg<sup>1</sup> )

3000 1100 50 [64]

) Number of cycles Ref.

(mAhg<sup>1</sup> )

.

Zinc Oxide Based Nano Materials and Devices

Method Initial capacity

Electrochemical characteristics of graphene in Li-ion batteries.

CM Reversible capacity (mAhg<sup>1</sup>

Reduction with autoclaved N2H4

(DODA-Br)

Table 3.

Table 4.

126

decreased to 318 mAhg<sup>1</sup>

, but the retention capacity

, the ZnO particles

Number of cycles

Ref.

The evidences reported in the scientific literature show an open thematic for the design of composite materials with the intention of directly impacting on this time of tool for the storage of electrochemical energy, being the ZnO-graphene system a great candidate to be used as a constituent material of the anode.

### Acknowledgements

The authors are grateful for the support granted in the Call 2019 issued by the Program of Support for Scientific and Technological Research in the Educational Programs of the Federal, Decentralized Technological Institutes and Centers belonging to the National Technological of Mexico (TecNM) for the support assigned to the Project (5269.19-P); and to the Higher Technological Institute of Irapuato (ITESI) for the allocation of support from its Institutional Program for the Strengthening of Academic Staff (PIFOCA/PIFOPA/PIICYT 2019).

Zinc Oxide Based Nano Materials and Devices
