Lithium dendrite problems affect the development of lithium battery, can quickly reduce the performance of the battery

Lithium metal is as high as 3860 MAH/g specific capacity and as low as 3.04 V (relative standard hydrogen electrode) oxidation reduction potential. Thus rechargeable lithium metal The battery become the most potential one of high-energy secondary rechargeable battery system. But lithium dendrite problems affect the development of lithium batteries, lithium dendrite of runaway growth can degrade the performance of the battery quickly, shorten the service life of the battery, even pierced, the membrane between the electrodes causes the security issues such as battery short circuit.

Therefore, how to in large current density, large energy density, long cycle conditions, achieve the effective inhibition on lithium dendrite growth becomes the key problem. Because of this, Japan's industrial technology research institute, Dr Bai Songyan Dr Sun Yang and Nanjing university professor Zhou Haoshen, developed a new type of MOF, electrolyte, can inhibit under large current high capacity lithium dendrite growth.

The research highlights:

1. MOF based electrolytes in the large current density, large energy density, long cycle, achieve the effective inhibition on lithium dendrite growth.

2. Through calculation, proved that the structure of MOF TFSI? Ion of effective regulation and realize uniform Li + ion transport.

The TOC figure

MOF based electrolytes is the use of MOF (HKUST) orderly superfine pore structure as ionic sieve, in ordinary electrolyte mlitfsidol/DME (1) to implement effective regulation of ion transport of Yin and Yang, and demonstrate high ion migration coefficient and high ionic conductivity. Relative to the ion of Yin and Yang in the disorder of ordinary electric hydraulic transmission and cause uneven lithium deposits, MOF structure can provide efficient ion channels, selective slow TFSI? Positive ions through in it, so as to achieve uniform effect of lithium ion transport, realize the homogeneous lithium deposits.

Figure 1 inhibited the growth of the lithium dendrite

To illustrate the MOF channel mechanism of ion transport work of Yin and Yang, the researchers made a series of theoretical calculation. With density functional theory (DFT) calculation in two extreme cases, TFSI? Positive ions in a horizontal (Path - I) or vertical (Path - II) cases by MOF channel of energy barriers. The MOF frame, rigid or relaxation conditions between them (F and F ') to base difference is 1.26 EV and 0.63 EV, respectively. Related calculation illustrates the MOF channel space constraints on TFSI? Positive ions in the channel transmission had selective delay effect.

Figure 2 DFT calculations TFSI? In MOF holes in the transmission of energy barriers

Molecular dynamics (MD) simulation results prove that the MOF structure can through to the TFSI? Anionic effective regulation to achieve uniform Li + ion transport. In the ordinary electro-hydraulic mlitfsidol/DME (1), the solvation process, TFSI? Anionic all azimuth shift is quicker than the solvation of the Li + ions. In MOF based electrolytes, MOF channel delay TFSI? Anion through in it, makes the Li + ions are azimuth shift spread faster.

Figure 3 li + and TFSI in ordinary DOL/DME and MOF based electrolyte electrolyte in the molecular dynamics simulation

Relative to the ion of Yin and Yang in the disorder of ordinary electric hydraulic transmission and cause uneven lithium deposits, MOF structure can provide efficient ion channels, selective delay TFSI? Positive ions through in it, so as to achieve uniform effect of lithium ion transport, realize the homogeneous lithium deposits.

Symmetric battery test respectively in the large current density (5 ma/cm2, ma/cm2) 10 ma/cm2 and 10 cases, its corresponding to the energy density of MAH/cm2 (2.5 MAH/cm2, 5 and 10 MAH/cm2) symmetric battery can be in long cycle time, at least no obvious signs of short circuit occurred in more than 800 hours.

Figure 4 mof based electrolytes in symmetric battery performance

Through SEM observation, lithium dendrite growth in after the cycle of lithium metal anode. Using traditional symmetrical electrolyte battery, in 10 MAH/cm2 and under the condition of 10 MAH/cm2, batteries in 120 hours after a short circuit. Lithium metal anode surface growth of a large number of up to 10 microns lithium dendrite pierced diaphragm cause short circuit. But in the use of MOF base electrolyte battery, lithium dendrite was obviously inhibit the growth of the situation. In three large current density under the condition of cases, there were no obvious lithium dendrite growth.

Figure 5 lithium metal electrode surface morphology changes under different current density

lithium titanate used as electrode materials, verified under the condition of high current, use the MOF base electrolyte of lithium battery, also can show the stability of the long cycle performance. In current density reach 7 ma/cm2, lithium titanate - lithium battery after the loop 2000 times, only 7 MAH/cm2 capacity loss. Each lap capacity loss rate as low as 0.0025%.

Figure 6 mof based electrolytes in lithium batteries, electrochemical performance test

In a word, the study first reported the role of MOF based electrolytes in lithium cathode protection, has important significance for the further development of lithium battery. In addition, the study also shows the MOF ultramicro pore structure of its potential applications in battery system.

BaiS,SunY,YiJ,etal.High-PowerLi-MetalAnodeEnabledbyMetal-OrganicFrameworkModifiedElectrolyte[J].Joule,2018.

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