Composite solid electrolyte and preparation method thereof

Abstract

The invention discloses a composite solid electrolyte and a preparation method thereof. The composite solid electrolyte is at least prepared from a sulfide solid electrolyte layer and an amorphous oxide solid electrolyte layer. By adopting the composite solid electrolyte, the amorphous oxide solid electrode is compounded on the surface of the sulfide solid electrolyte layer, so that the interfaceproblem between the sulfide solid electrolyte and an electrode material is solved. Meanwhile, a hot-press molding manner is adopted to ensure a good compounding effect on an heterogeneous interface (oxide / sulfide interface).

Description

technical field [0001] The invention relates to the technical field of lithium ion batteries, in particular to a composite solid electrolyte and a preparation method thereof. Background technique [0002] The ever-increasing consumption of digital electronics and the emerging electric vehicle industry have put forward higher requirements for energy storage devices. Lithium secondary batteries have many advantages such as high energy density, excellent cycle performance, no memory effect and no environmental pollution, and are favored by the market. However, lithium-ion batteries using organic electrolytes are gradually stretched in the face of the market's increasingly high requirements for safety, energy density, and cycle life. [0003] All-solid lithium secondary batteries using solid electrolytes have incomparable safety compared to liquid lithium secondary batteries, and are expected to completely eliminate potential safety hazards during use, and are more in line with...

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Problems solved by technology

However, the single sulfide electrolyte still has the following problems: (1) the high price of Ge in the sulfide 4+ It is unstable to metal lithium. If it is in direct contact, it will be reduced by Li to form a low-conductivity impurity phase; (2) The chemical potential difference between the sulfide and the oxide positive electrode is large, and the oxide electrode is an electron-ion mixed conductor, which is easy to form Wide Schottky-type space charge layer, resulting in large interfacial impedance; (3) The shear modulus of cold-pressed sulfide is low, and the effect of inhibiting lithium dendrites is not ideal

[0014] The main problem is that although amorphous oxides are softer than crystalline oxides and can improve solid-solid contact to a certain extent, based on oxide electrolytes and homogeneous oxide amorphous The surface modification in the state is still an oxide in essence, and it cannot combine the advantages of different electrolytes to improve the overall performance, so the following problems still exist:

[0015] (1) The conductivity of the oxide electrolyte is low, and the conductivity of the oxide after the amorphous state will be damaged to a certain extent. Therefore, the conductivity of the electrolyte obtained by this scheme is lower than that of the traditional oxide electrolyte. The energy storage density and power density of the solid-state battery based on it are poor;

[0016] (2) The oxide electrolyte matrix is ​​still very hard, although a layer of amorphous oxide is coated on the negative electrode side, but due to the low conductivity of the amorphous oxide, the reasonable thickness of the amorphous layer is small, It cannot completely buffer the volume expansion of the negative electrode during charging and discharging.

[0020] The main problem of its existence is: although in high conductivity Li 10 GeP 2 S 12 A relatively high stability Li is introduced between the Li-containing anode 2 S-P 2 S 5 -P 2 o 5 The interface reaction on the Li negative electrode side can be suppressed to a certain extent, and relatively high conductivity can be retained. However, the same as the above, the simple use of sulfide still has shortcomings in terms of overall performance, and the following problems still exist in this scheme:

[0021] (1) The sulfide itself is relatively soft and can be well combined with the positive and negative electrodes, but at the same time its mechanical strength is lower than that of oxides, and it is less effective than oxides in inhibiting Li dendrites;

[0022] (2) There is a large chemical potential difference between the sulfide electrolyte and the oxide electrode. Therefore, when matching with the current commercial oxide electrode, a very wide Schottky type space charge layer will be formed, resulting in a very large interface impedance. , deteriorating the performance of solid-state batteries

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