| Lithium ion batteries is the most wide range of energy storage technology due to its large capacity, light quality, long service life, no memory effect, etc.. Currently, the higher reqirement on the super performance of lithium ion battery is essential for the development of electronic appliances like cellphone, hybrid car and so on. Of the components of lithium ion battery, electrode materials are the key obstacle for its performance throughout the history of the lithium ion battery developement. Two-dimensional layered materials are the promising anode materials for lithium ion battery owing to its excellent proper ties of lithium storage. Recently, a new type of two-dimensional layered materials MXene drew wide attentions of lithium ion battery related researching community. Two-dimensional layered materials MXene is similar to graphene, owning large specific surface area which makes it has excellent lithium storage property. In addition, the adjustable layer spacing plays a dominant role apart from other significant advantages of 2D layered materials. All of these make 2D layered materials a very potential lithium-ion battery anode. Herein, this paper focuses on two of the MXene materials, Tin+1Al Cn(n=1, 2). The main work is to study the synthesis and electrochemical performance of Tin+1Al Cn in detail.First of all, the experiments about how to synthesize the MXene and the property characterization were conducted. In order to etch the Al out of the materials, the Ti2 Al C powders were submerged in the HF solution with different concentrations ranging from 10 wt% to 40 wt%. The results indicated the best conditions of etching were that the HF concentration was 40 wt% and the etching time was 4h. Refer to the above experimental results, the best processing conditions for HF concentration is 40wt%, and the etching time was 6 h. The yields of Ti2 CTx and Ti3C2 Tx were about 6% and 85%, respectively. By comparing the etching results and yield rate, Ti3C2 Tx is more suitable than Ti2 CTx for application in lithium ion batteries for the following study. Second, with respect to exfoliating Ti3C2 Tx material, the results show that embedding DMSO into Ti3C2 Tx immediately followed by exfoliating has the best effect, which is contributed to the water absorption properties of dimethyl sulfoxide. In this dissertation, we can get better Ti3C2 Tx single layer by using dimethyl sulfoxide when exfoliating Ti3C2 Tx with the detaching conditions of ultrasonic power 150 W and ultrasonic time for 4 h with low speed centrifuge. If only embedding dimethyl sulfoxide Ti3C2 Tx layers without simultaneous ultrasound, we just can obtain the Ti3C2 Tx with expanded layer space. Transmission Electron Microscopy(TEM) results show that the distance between layers was obviously increased from from 21 layers of 20 nm to 17 layers of 20 nm after the dimethyl sulfoxide embedding. In our experiment, it was found that a layer of the amorphous Ti O2 was formed after treating the powders in the boiling water for 4 h instead of forming the single layer of Ti3C2 Tx as expected. The formed Ti O2 layer was benefitial to the electrochemical performance in terms of the capacity and ohmic resistance.Secondly, we thoroughly studied the electrochemical performance of Ti3C2 Tx as anode for lithium ion battery. And in this part, many methods were adopted to further improve the electrochemical performance, such as capacity and stability of the anode.(1)When Ti3C2 Tx was directly used as the anode material for lithium ion batteries, the capacities of the battery were 100 m Ah/g after running as many as 100 times at the rate of 1 C. As far as the ratio performance is concerned, under the condi tions of 0.1, 0.2, 0.5, 1 and 2 C, its capacities were 167, 135, 115, 105 and 94 m Ah/g, respectively. These results indicate the capacity attenuation was small as the discharging rate increased. However, the reversibility of the battery needs to be improve d. By the alternating-current impedance results, it can be seen that Rct was as high as 459.5 Ω and it became to 109.1 Ω after running as many as 100 times.There is a layer of F、O/OH groups on the surface of Ti3C2, which have a great impact on the electrical conductivity of Ti3C2 Tx.(2)After treating Ti3C2 Tx in boiling water, the cycle performance was about the same when compared with before treatment; however the Rct decreased to 25.9 Ω. The rate performance is improved as well.(3)Embedding the dimethyl sulfoxide into Ti3C2 Tx interlayer can effectively achieve the role of i ncreasing layer spacing which is benefitial for lithium-ion intercalation and deintercalation. Both cycle performance and rate performance were greatly improved with the increment ranging from 30 to 50 m Ah/g. Furthermore, the Rct was reduced to 29.5 Ω.(4)With respect to using the Graphene/Ti3C2 Tx composite materials as the anode materials for lithium ion batteries,,it was found that graphene / Ti3C2 Tx can mixed more evenly in solution, therefore the electrochemical performance of method is better. After mi xing graphene/Ti3C2 Tx composite in solution, cycle performance has been greatly improved, the capacity of 1 C increased from 100 to 185 m Ah/g. The rate performance under the different rate increased for 60-100 m Ah/g; when switched back to 0.1 C, the capacity returned to the initial value of 250 m Ah/g. The reversibility of the battery has greatly improved.In conclusion, the best experimental conditions for etching Ti3 Al C2 were identified as that etching the powders in 40 wt% concentration of HF for 6 h. When used as the anode materials for lithium ion battery, the reversibility needs to be further improved because there are some F、O/OH groups on surface of Ti3C2 Tx which compromise the conducting property. When using the Graphene/Ti3C2 Tx composite materials as the anode materials for lithium ion batteries, the cycle performance, rate capacity as well as the conductivity have been greatly improved. The results in this dissertation about Ti3C2 Tx material with excellent electrochemical performance make it a promising anode material for lithium-ion battery. |
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