Framework supported solid-state electrolyte composites for all-solid-state batteries

An all-solid-state battery system having a solid-state electrolyte composite is provided. The solid-state electrolyte composite includes a porous framework providing support and mechanical strength for the solid-state electrolyte composite and a plurality of ionic conductors filling voids of the porous framework for maximizing ionic conductance of the solid-state electrolyte composite. The porous framework may be made of ultra-high-molecular-weight polyethylene (UHMWPE) polymers and the plurality of ionic conductors may be made of poly(ethylene oxide)-LiN(SO2CF3)2 (PEO-LiTFSI) polymers. The all-solid-state battery system includes battery cells each including a cathode current collector, a cathode disposed beneath and connected to the cathode current collector, the solid-state electrolyte composite disposed beneath and connected to the cathode, an anode disposed beneath and connected to the solid-state electrolyte composite, and an anode current collector disposed beneath and connected to the anode.

FIELD OF THE INVENTION

The subject invention relates to the solid-state electrolyte for all-solid-state batteries. More particularly, the invention relates to an ultrathin polymer framework supported solid-state electrolyte composite with high ionic conductance and enhanced mechanical strength for all-solid-state batteries.

BACKGROUND OF THE INVENTION

All-solid-state batteries have been widely recognized as an alternative solution to the conventional batteries using non-aqueous electrolytes. The employment of solid-state electrolyte alleviates safety concerns and promotes direct use of alkaline metals, such as Li, Na, K, as the battery anodes to break through the energy bottleneck.

Several examples of solid-state electrolyte solutions are found in CN patent applications CN 106654276 A and CN 110137568 A. Fillers such as alumina, titanium oxide and sulfide or ceramic type ionic conductors were utilized to reduce the polymeric crystallinity. However, these methods could barely enhance mechanical properties of the battery systems. In some other patents including U.S. Pat. No. 10,566,652 B2, multi-layered electrolytes were designed to integrate the beneficial properties of multiple materials into one battery system. Nevertheless, issues including large dimensions and low conductance were still not resolved.

Despite all the efforts, it is still challenging for the existing solid-state electrolyte composites to meet the requirements of various applications for both high ionic conductance and enhanced mechanical strength.

BRIEF SUMMARY OF THE INVENTION

There continues to be a need in the art for improved designs and techniques for all-solid-state battery systems to provide enhanced mechanical property and high ionic conductance to promote performance of the all-solid-state battery systems.

Embodiments of the subject invention pertain to a framework supported solid-state electrolyte composite including at least one ionic conductor providing the ionic conductivity and at least one porous framework providing the mechanical strength for the solid-state electrolyte composite.

According to an embodiment of the subject invention, a solid-state electrolyte composite for a solid-state battery comprises a porous framework for providing support and mechanical strength for the solid-state electrolyte composite and a plurality of ionic conductors filling voids of the porous framework for maximizing ionic conductance. The porous framework comprises a plurality of units interconnected into one or more patterns, forming a continuous network. Moreover, the porous framework comprises a porous three-dimensional (3D) structure or a porous two-dimensional (2D) structure. The porous framework may be made of ultra-high-molecular-weight polyethylene (UHMWPE) polymers and the plurality of ionic conductors may include poly(ethylene oxide)-LiN(SO2CF3)2(PEO-LiTFSI) polymers. The solid-state electrolyte composite supported by the porous framework may have a shape of a film or a slab and a thickness of about 3 μm. The porous framework is configured to have an effective framework porosity of about 40% to obtain a tensile strength of about 550 Mpa and a puncture resistance of about 1.5 N μm−1. Furthermore, the PEO-LiTFSI polymers of the plurality of ionic conductors may have a ratio of ethylene oxide (EO) to lithium-ion of about 10:1 to obtain a lithium-ion conductivity of 1.8*10−5S cm−1at a temperature of 22° C.

In another embodiment of the subject invention, an all-solid-state battery cell comprises a cathode current collector, a cathode disposed beneath the cathode current collector, a solid-state electrolyte composite disposed beneath the cathode, comprising a porous framework for providing support and mechanical strength for the solid-state electrolyte composite and a plurality of ionic conductors filling voids of the porous framework for maximizing ionic conductance, an anode disposed beneath the solid-state electrolyte composite, and an anode current collector disposed beneath the anode. Moreover, the cathode current collector can be made of aluminum (Al), the cathode can be made of lithium iron phosphate (LiFePO4), conductive carbon Super P, and PEO-LiTFSI, the anode can be made of lithium (Li), and the anode current collector can be made of copper (Cu). Further, the all-solid-state battery cell can be configured to have a specific capacity of about 140 mAh g−1when the all-solid-state battery cell is operated at a 1.0 C charge/discharge rate and to retain 93% of an initial specific capacity after 900 cycles of charging/discharging at a 1.0 C charge/discharge rate.

DETAILED DISCLOSURE OF THE INVENTION

When the term “about” is used herein, in conjunction with a numerical value, it is understood that the value can be in a range of 90% of the value to 110% of the value, i.e. the value can be +/−10% of the stated value. For example, “about 1 kg” means from 0.90 kg to 1.1 kg.

In describing the invention, it will be understood that a number of techniques and steps are disclosed. Each of these has the individual benefit and each also is used in conjunction with one or more, or in some cases all, of the other disclosed techniques. Accordingly, for the sake of clarity, this description will refrain from repeating every possible combination of the individual steps in an unnecessary fashion. Nevertheless, the specification and claims should be read with the understanding that such combinations are entirely within the scope of the invention and the claims.

In the following description, for purposes of explanation, numerous specific details are set forth in order to provide a thorough understanding of the subject invention. It will be evident, however, to one skilled in the art that the subject invention may be practiced without these specific details.

The subject invention will now be described by referencing the appended figures representing preferred embodiments.

All-Solid-State Battery Cells Comprising Framework Supported Solid-State Electrolyte Composites

FIG.1Ashows the structure of one example of the framework supported solid-state electrolyte composite100in a form of a thin film according to various embodiments of the subject invention. The framework supported solid-state electrolyte film100can comprise a porous framework110serving as a skeleton of the solid-state electrolyte composite100and a plurality of ionic conductors120that fills voids of the porous framework110.

As illustrated inFIG.1A, the porous framework110can comprise a plurality of units interconnected into one or more patterns, creating a continuous network. As a result of the continuously interconnected network structure, the porous framework110provides advantages including enhanced mechanical strength and improved integrity for the framework supported solid-state electrolyte composite100.

In one embodiment, the porous framework110may have a porous two-dimensional (2D) structure.

In another embodiment, the porous framework110may have a porous three-dimensional (3D) structure.

In preferred embodiments, the porous framework110can be made of, for example, ultra-high-molecular-weight polyethylene (UHMWPE) polymers, and the plurality of ionic conductors120can be made of, for example, poly(ethylene oxide)-LiN(SO2CF3)2(LiTFSI) (PEO-LiTFSI) polymers. In preparation of the framework supported solid-state electrolyte film100, the plurality of ionic conductors120such as poly(ethylene oxide)-LiN(SO2CF3)2(LiTFSI) (PEO-LiTFSI) polymers is immersed into the porous framework110made of, for example, ultra-high-molecular-weight polyethylene (UHMWPE) polymers. The ionic conductors120are infiltrated into the structure of the porous framework110and fill the interspace between the continuous network, forming the framework supported solid-state electrolyte composite film100.

In one embodiment, the ionic conductors120are configured to entirely fill the pores of the porous framework110.

In another embodiment, selected additional components, such as fillers, plasticizers, or different types of ionic conductors, can be added together with the ionic conductors120to fill the interspace of pores of the porous framework110, in order to improve certain aspects of the performance of the framework supported solid-state electrolyte composite film100. For example, the fillers including but not limited to, alumina, silica, titanium oxides, can be added to enhance the ionic conductivity and mechanical property or facilitate the electrolyte-electrode interface formation. In another example, the plasticizers may include but are not limited to succinonitrile (SN) or ethylene carbonate (EC). In yet another example, the ionic conductors may include but are not limited to Li7La3Zr2O12(LLZO) or Li10GeP2S12(LGPS).

In preferred embodiments, the framework supported solid-state electrolyte composite film100may have a thickness smaller than 10 μm, preferably smaller than or equal to 3 μm.

In preferred embodiments, the framework supported solid-state electrolyte composite film100can have an effective framework porosity of around 40%, achieving ultra-high tensile strength of about 550 Mpa and a puncture resistance of about 1.5 N μm−1with a film thickness of about 3 μm.

In preferred embodiments, a ratio of ethylene oxide (EO) to lithium-ion of the PEO-LiTFSI composites of the plurality of ionic conductors may be configured to be about 10:1 such that a lithium-ion conductivity of 1.8*10−5S cm−1at a temperature of 22° C. can be obtained.

In one embodiment, the lithium-ion conductivity of the fabricated framework supported solid-state electrolyte film100is about 1.5*10−5S cm−1at a temperature of 22° C.

Comparing with a conventional PEO-LiTFSI film having a thickness of about 200 the framework supported solid-state electrolyte composite film100of the subject invention having a film thickness of about 3 μm achieves a lithium-ion conductance that is more than 30 times greater.

FIG.1Bshows the structure and the stacking sequence of one preferred embodiment of the all-solid-state battery cell200comprising the framework supported solid-state electrolyte film100ofFIG.1A, according to various embodiments of the subject invention. The all-solid-state battery cell200comprises a cathode current collector210, a cathode220, the framework supported solid-state electrolyte film100, an anode230, and an anode current collector240.

In one embodiment, the cathode current collector210is disposed on the cathode220that is in turn disposed on the framework supported solid-state electrolyte film100, and the framework supported solid-state electrolyte film100is disposed on the anode230that is in turn disposed on the anode current collector240.

Moreover, the cathode current collector210may be disposed to be in direct contact with the cathode220. Similarly, the cathode220may be disposed to be in direct contact with the framework supported solid-state electrolyte film100, the framework supported solid-state electrolyte film100may be disposed to be in direct contact with the anode230, and the anode230may be disposed to be in direct contact with the anode current collector240.

In one embodiment, the cathode current collector210is made of a metal material such as aluminum (Al).

In one embodiment, the cathode220is made of for example, lithium iron phosphate (LiFePO4), conductive carbon Super P, and PEO-LiTFSI.

In one embodiment, the anode230is made of, for example, a metal material such as lithium (Li).

In one embodiment, the anode current collector240is made of a metal material such as copper (Cu).

Characterization Tests

Referring toFIG.2, the rate capabilities of the all-solid-state battery cell200comprising the framework supported solid-state electrolyte film100are tested at a temperature of about 60° C. In these tests, lithium iron phosphate is selected as the cathode material and the lower and upper cut-off voltages are set to be 2.5V and 3.8V, respectively. It is observed that when the all-solid-state battery cell200is controlled to have a 1.0 C charge/discharge rate, a specific capacity of about 140 mAh g−1can be achieved. Further, it is observed that when the all-solid-state battery cell200is controlled to have a 0.1 C charge/discharge rate, a specific capacity of about 149 mAh g−1can be achieved.

Now referring toFIG.3, the cycling performance of the all-solid-state battery cell200comprising the framework supported solid-state electrolyte film100is tested at a temperature of about 60° C. In these tests, the lower and upper cut-off voltages are set to be 2.5V and 3.8V, respectively. The all-solid-state battery cell200is charged and then discharged for a duration of 900 cycles at a 1.0 C charge/discharge rate. Although the specific capacity of the all-solid-state battery cell200gradually decreases over the cycling time, a specific capacity of about 93% of the initial specific capacity (measured at the beginning of the tests) can be retained after the 900 cycles of testing.

Referring toFIG.3again, during the tests, it is observed that the coulombic efficiency of the all-solid-state battery cell200barely changes after 900 cycles of testing and remains at about 100% throughout the cycling processes.

Although the subject invention has been illustrated and described herein with reference to preferred embodiments and specific examples thereof, it will be readily apparent to those of ordinary skill in the art that other embodiments and examples may perform similar functions and/or achieve like results.

REFERENCES