Using frozen electron microscopy to observe battery materials and interface atomic structure technology

【introduction】

The all-solid-state lithium-ion battery uses a solid electrolyte instead of the traditional liquid organic electrolyte, which effectively avoids the hidden dangers of the safety, thermal stability and electrochemical stability of the conventional lithium-ion battery, making it a large battery and a super-super The thin battery field has considerable application potential. However, the solid-state batteries currently studied are far inferior to liquid lithium-ion batteries in terms of rate performance and cycle performance. This is due to the larger interfacial contact resistance of the electrode-solid electrolyte in solid-state batteries, and the grain boundary resistance determines the overall ion conductance of the electrolyte. Rate, so the interface compatibility problem mainly affects the electrochemical performance of the battery. However, there are not many effective methods for characterizing the solid-solid interface in current solid-state batteries. Solid-state NMR is a non-destructive, highly selective test method for materials. It mainly examines the interaction between nucleus and nucleus and the local microenvironment of each atom by chemical shift changes in solid-state NMR spectroscopy. The body phase information in the battery material (electrode material and solid electrolyte) is detected. Solid-state NMR can detect battery lithium-containing multiphase material system (between the plurality of electrode materials such as lithium-containing or lithium-containing electrode material and a lithium-containing electrolyte between a) the spontaneous lithium ion exchange, whereby a charge in a multiphase Selective information transmitted in the interface. The structure of the all-solid lithium-ion battery includes a positive electrode, an electrolyte, and a negative electrode, all of which are composed of a solid material, and Li6PS5X (X=Cl, Br) is a high lithium ion room temperature conductivity (>10-3 S/cm). Ion conductor for solid electrolytes in all solid state lithium ion batteries.

[Introduction]

Recently, Professor Marnix Wagemaker (Corresponding author) (Dr. Yu Chuang, Dr. Swapna Ganapathy, co-first author) of the Delft University of Technology in the Netherlands published in the journal Nature Communications entitled "Accessing the bottleneck in all-solid state batteries". , Li-ion transport over the interface between the solid-electrolyte and electrode". In this paper, the two-dimensional lithium ion exchange solid-state nuclear magnetic method is used to study the spontaneous lithium ion transport between the sulfide cathode material (Li2S) and the solid electrolyte (Li6PS5Br) interface, so as to study the preparation method of sulfide cathode material and solid electrolyte mixture. The number of battery cycles has an effect on lithium ion transport between Li2S and Li6PS5Br. The results show that the interfacial conductivity between the two materials is heavily dependent on the preparation method of the mixture, and the charge-discharge cycle will break the interface contact between the two, increasing the energy barrier of lithium ion diffusion, resulting in interface conductivity. Reduced.

[Graphic introduction]

Figure 1. Chemical processing at different stages of an all-solid-state battery material and capacity retention at its corresponding stage

a. Treatment of battery positive-electrolyte mixture by simple mixing, ball milling, heat treatment (I simply mixed micro-Li2S, II simple mixed nano-Li2S, III ball-milled blended nano-Li2S, IV heat-treated blended nano- Li2S).

b. Battery capacity after cyclic charge and discharge of the electrode-electrolyte mixture in the different treatment stages described above.

Cf. Charge-discharge curves for the electrode-electrolyte mixture at different stages of treatment (charge and discharge current density 0.064 mA cm? 2, voltage window 0-3.5 V).

Figure 2. NMR test of spontaneous emission of lithium ion at Li2S positive electrode-Li6PS5Br solid electrolyte interface

Aii One-dimensional 7Li magic angle rotating MAS spectrum corresponding to the electrode-electrolyte mixture of the different treatment stages (I-III) described above.

Bcd Sample processing Stage I electrode-electrolyte mixture corresponding to a two-dimensional 7Li-7Li solid-state nuclear magnetic exchange spectrum.

Fgh Sample processing stage II electrode-electrolyte mixture corresponding to a two-dimensional 7Li-7Li solid-state nuclear magnetic exchange spectrum.

The jkl sample processing stage III electrode-electrolyte mixture corresponds to a two-dimensional 7Li-7Li solid-state nuclear magnetic exchange spectrum.

(The sample in which I-II is simply mixed has no obvious "out-of-diagonal anti-cross", indicating that the lithium ion exchange effect is weak in the process, and the "diagonal anti-cross" of the sample mixed by the ball milling method appears in At 10ms, it indicates a significant lithium ion exchange at the positive-solid electrolyte interface.)

Fig. 3 The crystal plane behavior of Li metal dendrites

Figure 4 Atomic resolution TEM analysis of Li metal dendrites and SEI interface