KR20230093889A - All-solid-state battery with high chemo-mechanical stability - Google Patents

Abstract

The present invention provides an anode current collector, a pyrolytic graphite sheet (PGS) disposed on the anode current collector, and an anode active material disposed on the pyrolytic graphite sheet and made of a Li-Si alloy and a sulfide-based solid electrolyte. It relates to an all-solid-state battery having a negative electrode layer including a negative electrode active material layer containing a weight ratio of 70: 30 to 90: 10. The all-solid-state battery according to the present invention has a negative electrode containing a negative electrode active material (Li-Si alloy) and a sulfide-based solid electrolyte in a specific weight ratio, thereby increasing the contact area between the electrode and the electrolyte without affecting the capacity and reversibility of the battery. Since it can widen, short circuit and mechanical failure caused by oxidation/reduction reaction of solid electrolyte are prevented, and it has significantly improved chemical and mechanical properties compared to known technologies.

Description

All-solid-state battery with improved chemical-mechanical properties {ALL-SOLID-STATE BATTERY WITH HIGH CHEMO-MECHANICAL STABILITY}

The present invention relates to an all-solid-state battery, and more particularly, to an all-solid-state battery having a negative electrode designed to improve chemical and mechanical properties of an all-solid-state battery including a sulfide-based solid electrolyte.

Recently, as the demand for high-energy/high-capacity batteries increases due to the technological development and generalization of electric vehicles (EVs), high-performance portable devices, and energy storage systems (ESS), various researches on next-generation batteries are being actively conducted worldwide. there is.

However, issues related to stability have recently emerged due to the risk of explosion and ignition of lithium secondary batteries. This is because currently commercialized lithium secondary batteries use organic electrolytes that are vulnerable to evaporation, leakage, ignition, and explosion.

In order to solve these problems, an all-solid-state battery using a solid electrolyte instead of a liquid electrolyte has received a lot of attention and has been actively researched.

Types of solid electrolytes applied to all-solid-state batteries can be largely divided into sulfide-based electrolytes, oxide-based electrolytes, and polymer-based electrolytes. Among them, sulfide-based solid electrolytes are classified into amorphous glasses solid electrolyte, crystalline ceramic solid electrolyte, and glass-ceramics solid electrolyte in which crystal phase is precipitated in an amorphous structure according to crystallinity. Depending on the type, 10 ^-6 ~10 ^-1 S/ It has an ionic conductivity of cm. In addition, since the sulfide-based solid electrolyte has a low Young's modulus and good deformability, it has an advantage in that it can be processed by cold pressing.

However, the sulfide-based solid electrolyte has a disadvantage in that the electrochemical stability voltage window is narrow (1.7 to 2.1 V vs. Li/Li ⁺ ). When the operating voltage is outside the electrochemically stable range of the electrolyte, oxidation or reduction of the electrolyte occurs. Due to the generation of decomposition products, the ionic conductivity of the electrolyte in the electrode decreases and the internal resistance increases.

For example, sulfur composite cathode | 75Li ₂ S-25P ₂ S ₅ (LPS) electrolyte | In the case of an all-solid-state battery with a cathode/solid electrolyte/cathode structure of Li-Si alloy anode, the electrode potential of the cathode undergoes a voltage change of Li/Li ⁺ 0.94 to 3.56V during charging and discharging in the operating voltage range of 0.5 to 3.7V. (Fig. 1). Since this is a voltage outside the electrochemical stability range of the electrolyte, the LPS electrolyte is decomposed by an oxidation reaction during charging, and Li ions are irreversibly deposited at the interface between the anode and the electrolyte. As a result, lithium dendrites (Li-dendrite) are generated and a micro short circuit is formed, resulting in voltage noise during charging (FIGS. 2 to 4).

Therefore, in order to solve the intensive lithium deposition phenomenon at the interface caused by LPS decomposition, it is necessary to expand the reaction site where Li ions can be reduced.

International Publication WO 2020/067108 A1 (Publication date: 2020.04.02) Korean Patent Publication No. 10-2020-0128256 (published date: 2020.11.12)

The technical problem to be solved by the present invention is decomposition by oxidation/reduction reaction of sulfide-based solid electrolyte during charging and discharging, and short circuit phenomenon and mechanical destruction due to the generation of lithium dendrite (Li-dendrite) as a result. It is to provide an all-solid-state battery having a negative electrode capable of preventing mechanical failure.

In order to achieve the above technical problem, the present invention is an all-solid-state battery comprising a negative electrode layer, a positive electrode layer, and a sulfide-based solid electrolyte layer provided between the negative electrode layer and the positive electrode layer, wherein the negative electrode layer, (i) a negative electrode current collector, (ii) a pyrolytic graphite sheet (PGS) disposed on the negative electrode current collector, and (iii) a negative electrode active material disposed on the pyrolytic graphite sheet and made of a Li-Si alloy and a sulfide-based An all-solid-state battery comprising a negative active material layer containing a solid electrolyte in a weight ratio of 70:30 to 90:10 is proposed.

At this time, the negative electrode active material layer preferably includes Li _3.25 Si as a Li-Si alloy as a negative electrode active material and 75Li ₂ S-25P ₂ S ₅ as a sulfide-based solid electrolyte, more preferably, the negative electrode active material The layer may include Li _3.25 Si and 75Li ₂ S-25P ₂ S ₅ in a weight ratio of 80:20.

On the other hand, the positive electrode layer is preferably made of a composite containing sulfur, and for example, may be made of a composite containing sulfur, a sulfide-based solid electrolyte, and carbon.

And, the present invention is a method for manufacturing the all-solid-state battery in another aspect of the invention, (a) forming a solid electrolyte layer by pressing a sulfide-based solid electrolyte powder, (b) negative electrode active material powder made of a Li-Si alloy and sulfide-based solid electrolyte powder in a weight ratio of 70: 30 to 90: 10. Forming a negative electrode active material layer by providing a composite powder on one side of the solid electrolyte layer and pressurizing it, (c) a pyrolytic graphite sheet (pyrolytic). stacking a graphite sheet (PGS) on the negative electrode layer, and (d) providing a composite powder containing sulfur, a sulfide-based solid electrolyte, and carbon on the other side of the solid electrolyte layer, and pressurizing it. We propose a manufacturing method of an all-solid-state battery comprising the step of forming a positive electrode layer by doing so.

The all-solid-state battery according to the present invention has a negative electrode containing a negative electrode active material (Li-Si alloy) and a sulfide-based solid electrolyte in a specific weight ratio, thereby increasing the contact area between the electrode and the electrolyte without affecting the capacity and reversibility of the battery. Since it can widen, short circuit and mechanical failure caused by oxidation/reduction reaction of solid electrolyte are prevented, and it has significantly improved chemical and mechanical properties compared to known technologies.

1 is an electrode potential change curve (red line) of the cathode during discharge and charging of 0.5 to 3.7 V of an all-solid-state battery (Sulfur composite cathode|75Li ₂ S-25P ₂ S ₅ electrolyte|Li-Si alloy anode) .
2 is a discharge/charge curve of an all-solid-state battery having a negative electrode made of only a Li-Si alloy.
3 is a schematic diagram showing degradation products produced by oxidation/reduction of LPS (75Li ₂ S-25P ₂ S ₅ ) electrolyte.
4 is a scanning electron microscope (SEM) photograph of an all-solid-state battery having a negative electrode made of only a Li—Si alloy in a state of charge of 3.7 V.
5 is a schematic diagram of a full cell incorporating the composite anode structure fabricated in the present example.
6 is a discharge/charge curve (black) and a composite anode structure (negative electrode active material: electrolyte = 50: 50 wt%) of a cell to which the composite anode structure (negative electrode active material: electrolyte = 80: 20 wt%) manufactured in the present example is applied. ) is the discharge curve (red color) of the cell applied.

In describing the present invention, if it is determined that a detailed description of a related known function or configuration may unnecessarily obscure the gist of the present invention, the detailed description will be omitted.

Embodiments according to the concept of the present invention can be applied with various changes and can have various forms, so specific embodiments are illustrated in the drawings and described in detail in this specification or application. However, this is not intended to limit the embodiments according to the concept of the present invention to a specific disclosed form, and should be understood to include all changes, equivalents, or substitutes included in the spirit and technical scope of the present invention.

Terms used in this specification are only used to describe specific embodiments, and are not intended to limit the present invention. Singular expressions include plural expressions unless the context clearly dictates otherwise. In this specification, terms such as "comprise" or "having" are intended to designate that the described feature, number, step, operation, component, part, or combination thereof exists, but one or more other features or numbers However, it should be understood that it does not preclude the presence or addition of steps, operations, components, parts, or combinations thereof.

Hereinafter, the present invention will be described in detail with examples.

<Example>

According to the prior art, when the anode is composed of only lithium silicon (Li ₁₃ -Si ₄ ), a high-capacity anode active material, Li-dendrite due to irreversible Li ion deposition at the cathode/electrolyte interface under conditions outside the electrochemical stable voltage range of the electrolyte phenomenon appears. Therefore, it is necessary to disperse the Li-Si alloying reaction site by applying a 'composite' structure different from the existing anode structure composed of only anode active materials.

Therefore, in the embodiment according to the present invention, the contact area between the electrode and the electrolyte is increased without affecting the capacity and reversibility of the battery by adding a solid electrolyte while maintaining the existing negative active material content of the negative electrode as follows. A scalable all-solid-state battery is presented. In addition, in the all-solid-state battery according to the present invention, since a solid electrolyte having low electronic conductivity is added to the negative electrode, a pyrolytic graphite sheet (PGS) is additionally inserted between the negative electrode active material layer and the current collector for smooth electron movement.

1) Manufacturing sulfur composite cathode (sulfur+solid electrolyte+carbon)

Mix sulfur, solid electrolyte, and carbon at a ratio of 25:50:25 wt%, considering the volume ratio of components for cathode manufacturing. A planetary ball milling method was adopted for uniform dispersion of materials and particle size reduction. Put each component in powder form and a 5Φ zirconia ball in a BPR (ball to powder) 35 : 1 weight ratio in a milling pot, and seal it in a glove box to maintain the Ar atmosphere inside the milling pot. If planetary ball milling of the sealed milling pot at 370 rpm produces a composite cathode with uniform distribution.

2) Sulfide-based solid electrolyte (Li ₂ S-P ₂ S ₅ ) Preparation - Electrolyte preparation for performance evaluation of the present invention

A sulfide-based solid electrolyte that is easy to manufacture a bulk type all-solid-state battery and can minimize side reactions with a sulfur electrode is prepared. Among the sulfide-based solid electrolytes, Li ₂ SP ₂ S ₅ having relatively high ionic conductivity at room temperature is selected. Put 0.532 g of 75:25 mol% Li ₂ S powder and 0.858 g of P ₂ S ₅ powder together with 10 10 zirconia balls in a BPR 30:1 weight ratio in a milling pot. After that, planetary ball milling is performed at 370 rpm. Like the cathode, proceed in the glove box.

3) Anode (Li _3.25 Si) Manufacturing - Anode manufacturing for comparison with the present invention

Among the Li alloying elements, Li-Si alloy with high capacity per volume is manufactured and applied to the anode of the all-solid-state battery. Like the cathode and solid electrolyte, it is manufactured in a glove box. Put 0.2140g of granular Li and 0.2664g of Si powder into a milling pot, put 5Φ, 10Φ zirconia balls together under the BPR 110: 1 weight ratio condition, and then perform planetary ball milling at 370rpm.

4) Composite Anode (Li _3.25 Si + solid electrolyte) manufacturing - composite anode manufacturing for performance evaluation of the present invention

In order to disperse the lithium ion reduction (alloying and lithium precipitation) that can be concentrated at the interface between the electrolyte layer and the anode layer, a composite anode composed of an anode active material and a solid electrolyte is prepared. After putting 80:20 wt% Li _3.25 Si: (75Li ₂ S-25P ₂ S ₅ ) and 5Φ, 10Φ zirconia balls together in a milling pot, planetary ball milling is performed at 370 rpm. Like the existing anode, proceed in the glove box.

5) Manufacture of all-solid-state battery full cell (FIG. 5)

- Put 0.1g of electrolyte into an alumina mold with a diameter of 14Φ and apply a pressure of 330MPa with an oil pressure machine to form a disc pellet.

- Negative active material (Li _3.25 Si = 0.01g): A composite prepared by mixing electrolyte at a ratio of 80:20 wt% is placed on one side of the mold and pressure is applied to form an anode layer.

- PGS is laminated on the composite anode and pressure is applied to complete the anode layer.

- Put 0.02g of sulfur composite cathode on the opposite side of the mold and apply pressure to create a sulfur composite cathode layer. (Cathode active material S = 0.005 g, electrolyte = 0.01 g, carbon conductive material = 0.005 g)

6) Charge and discharge test for all-solid-state battery with composite anode

The ratio of the anode active material and the solid electrolyte of the composite anode was tested by adjusting to 50:50 wt% and 80:20 wt%. The battery to which the 50:50 wt% negative electrode was applied had an increased resistance due to the high electrolyte ratio, and a discharge capacity of 50 mAh/g was recorded (red graph in FIG. 6). On the other hand, in the case of a cell introducing a composite anode structure with a weight ratio of 80 : 20wt%, compared to a cell with an existing anode structure, it shows a similar level of capacity per weight and does not show noise caused by Li-dendrite, so it has basic performance. and chemical-mechanical stability were both excellent (black graph in FIG. 6).

The present invention is not limited to the above embodiments, but can be manufactured in a variety of different forms, and those skilled in the art to which the present invention pertains may take other specific forms without changing the technical spirit or essential features of the present invention. It will be understood that it can be implemented as. Therefore, the embodiments described above should be understood as illustrative in all respects and not limiting.

Claims (5)

cathode layer; anode layer; And a sulfide-based solid electrolyte layer provided between the cathode layer and the anode layer,
The cathode layer,
negative current collector; a pyrolytic graphite sheet (PGS) disposed on the negative current collector; and a negative active material layer disposed on the pyrolytic graphite sheet and including a negative active material made of a Li-Si alloy and a sulfide-based solid electrolyte in a weight ratio of 70:30 to 90:10.
All-solid-state battery characterized in that it comprises. According to claim 1,
The Li-Si alloy is Li _3.25 Si,
The sulfide-based solid electrolyte is an all-solid-state battery, characterized in that 75Li ₂ S-25P ₂ S ₅ . According to claim 2,
The all-solid-state battery, characterized in that the negative electrode active material layer comprises Li _3.25 Si and 75Li ₂ S-25P ₂ S ₅ in a weight ratio of 80:20. According to claim 1,
The all-solid-state battery, characterized in that the positive electrode layer comprises sulfur, a sulfide-based solid electrolyte and carbon. (a) pressurizing the sulfide-based solid electrolyte powder to form a solid electrolyte layer;
(b) A composite powder containing a negative electrode active material powder made of a Li-Si alloy and a sulfide-based solid electrolyte powder in a weight ratio of 70:30 to 90:10 is provided on one surface of the solid electrolyte layer and then pressurized to form the negative electrode active material layer. forming;
(c) stacking a pyrolytic graphite sheet (PGS) on the negative electrode layer; and
(d) providing a composite powder containing sulfur, a sulfide-based solid electrolyte, and carbon to the other surface of the solid electrolyte layer, and then pressurizing to form a positive electrode layer; comprising
Method for manufacturing an all-solid-state battery.

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