EP4655830A1

EP4655830A1 - A separator

Info

Publication number: EP4655830A1
Application number: EP23918807.1A
Authority: EP
Inventors: Tu rul ÇET NKAYA
Original assignee: Sakarya University
Current assignee: Sakarya University
Priority date: 2023-01-26
Filing date: 2023-10-09
Publication date: 2025-12-03
Also published as: WO2024158360A1; TR2023000957A1

Abstract

The invention is to modify the separators, which are also used in other batteries or storage batteries, especially lithium batteries, with two-dimensional materials to improve their capacity conservation and cycle life and to increase the stability of the cathode materials in the system.

Description

A SEPARATOR

Technical Field of the Invention

The invention relates to a separator with a long cycle life and high-capacity retention properties, suitable for use in other batteries or storage batteries, especially lithium-ion batteries, which enables the stability of cathode materials to be improved, and the obtaining of said separators.

PRIOR ART

While a storage battery includes anode and cathode components as building blocks, it includes a separator in which isolation is provided between these two electrodes. The separator forms a catalyst in said system that allows the ions to move from the cathode to the anode during charging and vice versa during discharge. Ions are atoms that have had an electric charge by losing or gaining electrons. Although the ions can pass freely between the electrodes, the separator is an insulator without electrical conductivity.

The separators known in the art are generally obtained from very simple plastic films and have the correct pore size, which allows the ions to pass through while the other components cannot. In the art, separators are expected to have excellent porosity, low cost, light weight, and robustness. Polypropylene, polyethylene, and ceramic embedded materials are mostly used as separators in lithium-ion (Li-ion) and lithium -air (Li -air) battery technologies.

Lithium-ion batteries are at the forefront of electrochemical energy storage solutions, and in the coming years, a storage battery technology to be developed in an alternative commercial size cannot be predicted. Therefore, researchers in the relevant technical field are conducting many studies to improve the energy density of the current lithium-ion battery technology.

Some of the recent studies are for LiCoCh-based commercial cathode materials used as cathodes in lithium-ion batteries. Nickel and manganese doped lithium nickel manganese cobalt oxide (to be abbreviated as NMC) cathodes have been developed in the art due to the desire to increase the energy density of the storage batteries and the fact that the cobalt element is quite expensive. In order to reduce the amount of cobalt, NMC (811) based cathode materials were developed instead of NMC (333), where the nickel content was increased. In this cathode material, technical problems such as stability problems and the inability to maintain capacity in long cycle lives are seen.

It is predicted that the technical problems mentioned in lithium-ion batteries can be solved by studies on separators. There are some studies targeting this in the relevant technical field;

The subject matter of the patent application numbered WO201508845 1A1 relates to regulations on lithium sulfide batteries. A binder was used for the accumulation of graphene on the separator surface. Our invention is intended to increase the capacity conservations of lithium-ion batteries and to make the electrode stability stable over long cycles. Our method does not contain binders. Our two-dimensional materials accumulated in the separator ensure the rapid transfer of the electrolyte and its protection at the same time.

The subject matter of the patent application numbered US8470468 B2 relates to ceramic coating on the membrane surface. It is concluded that a high temperature-resistant storage battery can be produced with this method.

The subject matter of the patent application numbered US20130244119 Al relates to increasing the mechanical strength of the separator by preventing the evaporation of the electrolyte with the addition of graphene to the separator.

As a result, it has become a necessity in the relevant technical field to obtain separators with higher stability of the electrodes in the batteries or storage batteries, long cycle life and capacity conservation features.

Brief Description of the Invention

The invention relates to a separator suitable for use in energy storage devices in storage battery and battery technologies.

In one aspect, the invention relates to a separator for improving the properties of energy storage devices in battery and battery technology.

An object of the invention relates to a separator for eliminating the stability problems of the electrodes in the energy storage devices in the battery and storage battery technologies.

Another object of the invention relates to a separator with a long cycle life suitable for use in energy storage devices in battery and storage battery technologies.

Another object of the invention relates to a separator with high capacity retention values suitable for use in energy storage devices in battery and storage battery technologies.

The invention is a separator, suitable for use in lithium-ion batteries and storage batteries. DETAILED DESCRIPTION OF THE INVENTION

The subject of the invention in this detailed description is a separator having long cycle life and high-capacity retention features, suitable for use in other batteries or storage batteries, especially lithium-ion batteries, which provides the improvement of the stability of the cathode materials, as well as, and it is explained with examples that do not have any limiting effect only for a better understanding of the subject.

In the invention, "storage battery" refers to energy storage devices including a series and parallel connected system of generators that convert chemical energy such as batteries and accumulators into electrical energy. As is known, said storage batteries store electrical energy as chemical energy and this energy stored as chemical energy can be converted into electrical energy when desired. In general terms, storage batteries are systems in which the batteries are combined and stable together. Accordingly, the storage battery consists of batteries as a unit. Modification of each battery in the system will affect the characteristics of the final product storage battery. For example, if the amount of energy stored in the battery cells increases, the amount of energy that the final product storage battery can store will be just as high. Therefore, although the regulations on the batteries are explained in the invention, it is known that the final product will also affect the properties of the storage batteries.

In the invention, "lithium-ion batteries" mean energy storage devices consisting of anode carbon and cathode metal oxides, which usually contain an electrolyte consisting of lithium salts in the organic solvent and a separator that allows the separation of the electrodes.

In the invention, "electrode" refers to the conductor that may be caused by electric currents. Electrodes, as known in the art, are one of the essential elements of batteries, capacitors, and supercapacitors.

In the invention, "electrolyte" refers to an electrically conductive medium that does not conduct electrons thanks to the movement of the ions.

In the invention, "separator" refers to a permeable membrane that provides insulation and exchange of electrolyte ions between electrodes. In the invention, the words separator and decoupler are mentioned synonymously and mean the same things when they are interchangeable.

In the invention, "capacity retention" in the invention, it refers to the capacity retained as a percentage value when we compare the value we obtained after the first discharge capacity of the battery with the capacity values it has after a certain number of charge-discharge processes.

As is known in the present art, lithium-ion batteries are known to have low cycle life values due to the deterioration of the structure of the cathode electrode depending on the chargedischarge rates and operating voltage. In the present invention, technical solutions and advantages are presented to prevent these technical problems.

Lithium-ion batteries and storage batteries are mostly used as storage batteries in the relevant technical field. In the art, the main goal is to respond to today's energy needs, as well as to reduce costs and to research and develop lithium-ion batteries and storage batteries with long cycle life.

As is generally known in the art, metal oxides are used as cathode materials in lithium-ion batteries and storage batteries. Metal oxide, especially lithium-cobalt-oxide materials are used. Cathode materials have been developed in which nickel and manganese additives are made to lithium-cobalt-oxides to increase the energy density of said lithium-cobalt-oxide materials and to reduce the use of the high-cost cobalt element. The cathode materials developed in this way are consequently obtained from lithium-nickel-manganese-cobalt-oxide materials. In this way, the cathode materials obtained allow the use of less cobalt, reducing costs and increasing energy densities by creating a doped effect. Increasing the amount of nickel to reduce the use of more cobalt in lithium-nickel-manganese-cobalt-oxide cathodes in the relevant technical field causes stability problems of the cathode materials. This technical problem encountered in these cathodes causes the life of the cathodes to decrease and decreases in energy densities to be observed. In addition, high-performance separators should be included in the systems to meet today's energy storage needs in the relevant technical field. In particular, separators are expected to have lower self-discharge values, long cycle life and capacity conservation values of the system.

The subject of the present invention is related to separators to have all the mentioned features. The separators of the invention may preferably be one of the commercial separators that are common in the art. As mentioned earlier, separators using plastics such as polyethylene, polypropylene or ceramic-based materials frequently used in lithium-ion batteries can be used in the invention. The innovative aspect of the invention relates to the modification of separators. In the invention, the modified expression is the process of depositing the additive components on the substrate, which is the separator.

The components used in the modification of the separators of the invention were mainly obtained by the present inventors as a result of research and development activities to provide solutions to the stability problems of lithium-nickel-manganese-cobalt-oxide cathode materials with increased nickel content.

The components used in the process of modifying the separators of the invention are preferably more than one. If the number of said components is more than one, these components must be coexistent within the separator. These components can show a synergistic effect by contributing to each other's properties by coexisting in separators. Or, these components can only show their own effectiveness by remaining stable within the separator. Preferably, the component(s) with a two-dimensional structure are used as additives for the separators in the invention.

Molybdenum disulfide and graphene compounds are used as the components used in the process of modifying the separators subject to the invention.

As is known in the art, graphene and molybdenum sulfide are two-dimensional materials and these materials can be used in many areas due to their superior properties. In the case of lithium-ion batteries, the results obtained for these two-dimensional materials to increase the ionic diffusion rate and improve conductivity has been determined that a 2D material layer to be positioned between the separator and the cathode electrode can reduce the degradation behavior of the cathode electrodes, prevent the dissolution of cathode metals in the electrolyte as ions, and maintain a cathode structure that can remain stable at high current values with rapid ion transition. In practice, considering that the production of a separate two-dimensional membrane (can be abbreviated as 2D) as an application may cause extra cost, in the present invention, 2D materials are coated on the cathode side of the separator surface used in the battery cell and an intermediate layer is formed between the cathode and the separator. In the present invention, graphene and/or molybdenum sulfide materials are used as 2D materials. In a preferred embodiment, graphene is used as the 2D-size material. In a preferred embodiment, molybdenum sulfide is used as the 2D-size material. In a preferred embodiment, molybdenum sulfide and graphene are used together as 2D-size material.

The inventors preferably recommend the use of the vacuum filtration method for modified operations of separators. The vacuum filtration method is a separation method used to remove the solid from the liquid as known in the art. The innovative aspect of the invention is not related to the use of the vacuum filtration method and the scope of protection is not limited to said method. Other methods that work in the art in a similar way to the vacuum filtration method and serve the end purposes can also be used in the present invention. The inventors provide teachings on the coating of molybdenum sulfide and graphene components in separators as a novelty for the related technical field. Accordingly, the modified processes of the invention include the following steps; i. Adding at least one two-dimensional material to the DMF solution and ensuring homogeneous dispersion by means of a mixer, wherein said two-dimensional material is at least one or both of the graphene and/or molybdenum sulfide materials, ii. Placing the mixture obtained in step i) in the vacuum filtration device and ensuring that it adheres to the separator surface, iii. Subjecting the separator obtained in the process step ii) to drying processes.

In the process step i) mentioned herein, the two-dimensional material is between 1 mg/30 mL and 5 mg/75 mL in weight/volume in the solution.

The separator obtained as a result of the application of the process step iii) is preferably placed in a cell with LiPFe/EC: DMC as the anode and preferably the NMC (811) electrode as the cathode. It is an exemplary device created to show the effectiveness of the separator of the anode and cathode electrodes subject to the invention. The scope of protection of the invention is not limited to which materials the anodes and cathodes consist of. The object of the present invention is to modify the separators known in the art and used in Lithium-ion batteries with graphene and/or molybdenum sulfide two-dimensional components and to provide the technical solutions and advantages that this will provide. The separator of pure polypropylene, the NMC (811) cathode material known in the art as the separator, was used.

A high operating window of 3-4.5V was selected for the arrangement of the lithium-ion battery with the example arrangement (deep discharge and deep charging range were selected (to damage the electrodes)). A 200-cycle battery test was performed at a current rate of 1C (1- hour charge- 1 hour discharge). And the technical results obtained by applying this test are given in Figure 1. The molybdenum sulfide and/or graphene-modified separator of the invention may have greater capacity retention values of 20% to 30% than commercial separators used in the present art.

The molybdenum sulfide and/or graphene-modified separator of the invention may have longer cycle life values of 20% to 30% than commercial separators used in the present art. Although the separator of the invention seems to have arrangements that provide solutions to the technical problems encountered in lithium-ion storage batteries in the art, if preferred, it is used as separators that provide high performance in similar batteries and storage batteries. The modified separator obtained in the invention is suitable for use as a decoupler in all kinds of electric vehicles, solar and wind energy storage devices, and mobile devices.

The scope of protection of the invention is specified in the attached claims and cannot be limited to those explained for sampling purposes in this detailed description. It is evident that a person skilled in the art may exhibit similar embodiments in light of the above-mentioned facts without drifting apart from the main theme of the invention.

Claims

1. A separator suitable for use in batteries, especially in lithium batteries, to improve stability of cathode materials, comprising two-dimensional materials of graphene and/or molybdenum sulfide.

2. A method for obtaining the separator according to claim 1, characterized in that it comprises the following process steps: i. Adding at least one two-dimensional material to the DMF solution and ensuring homogeneous dispersion by means of a mixer, ii. Placing the mixture obtained in step i) into the vacuum filtration device and allowing it to adhere to the separator surface, iii. subjecting the separator obtained in the process step ii) to drying processes.

3. A method according to claim 2, characterized in that in step i) concentration of the two- dimensional material in the DMF is between lmg/30mL and 5mg/75mL in weight/volume.