What do you know about the positive and negative pole of lithium battery?

It is well known that the four major components constituting a lithium ion battery are a positive electrode material, a negative electrode material, a separator, and an electrolyte. However, in addition to the main four parts, the current collector for storing the positive and negative materials is also an important part of the lithium battery. Today we will talk about the positive and negative current collector materials of lithium batteries.

1, the current collector basic information

For lithium ion batteries, the positive set of the fluid in common use is aluminum foil, fluid is copper foil negative set, in order to guarantee stability of fluid inside the cell, the purity requirements both in more than 98%. With the continuous development of lithium battery technology, whether it is a lithium battery for digital products or a battery for electric vehicles, whether it is used for digital products of lithium batteries or the batteries of electric cars, we all hope the battery energy density is high, as far as possible the weight of the battery is more and more light, and in the collector, the most main is to reduce the thickness and the weight of the fluid, up from intuitive to reduce the volume and weight of the battery.

Li-ion battery with copper foil thickness requirements

Along with the rapid development in recent years, lithium electricity, lithium battery with set fluid development also soon. The anode aluminum foil by a few years ago the 16 reduced to 14 um, to 12 um, now has many battery manufacturers have production using 10 um foil, even use 8 um. And the cathode copper foil and copper foil flexibility is good, because itself by its thickness before 12 um reduced to 10, to 8 um, up to now there is a big part of the battery manufacturer to mass produce with 6 um, and some of the manufacturers are developing 5 um / 4 um are likely to use. Due to the lithium battery for use of copper foil are high purity, the density of material basic on the same level, with the loss of the thickness of the development, its surface density is reduced, the weight of the battery is also more and more small, in accordance with our demand for lithium batteries.

Li-ion battery with copper foil surface roughness requirements

For collection of fluid, besides its thickness weight influential to lithium batteries, set fluid surface performance for production and performance of the battery also has a great influence. Especially for the negative current collector, due to the defects of the preparation technology, the copper foil on the market is mainly composed of single-faced hair, double-faced hair, and double-faced roughening. The two negative sides coating contact resistance caused by asymmetric structure asymmetry, then make two negative capacity cannot even release; Asymmetric at the same time, the two sides also cause negative electrode coating bond strength, yes unbalanced charge-discharge cycle life of anode coating on both sides, thus accelerate the battery capacity attenuation.

By the same token, the anode aluminum foil is also as far as possible to the double symmetric structure development, but under the influence of aluminum foil preparation technology at present, the main or with a single light aluminum foil. Due to large thickness of aluminum foil is the basic of aluminum rolling, and the need to control in the process of rolling aluminum contact with roll, so usually on aluminum foil surface add lubricant, to protect the aluminum ingots and roll, and the surface of the lubricant has certain influence to the battery pole piece, therefore, for the aluminum foil surface except the lubricant is also a key factor.

Why does the copper foil use the negative electrode and the aluminum foil for the positive electrode?

First, the copper foil good electrical conductivity, texture soft, price is cheap. As we all know, the working principle of lithium-ion batteries convert chemical energy into electrical energy is an electrochemical device, so in the process, we need a medium that the chemical energy into electrical energy transfer, this requires conductive materials. And in ordinary material, metal material is the best material and electrical conductivity in metal material is cheap electrical conductivity and good copper foil and aluminum foil. At the same time, in the lithium battery, we are winding and laminated two kinds of processing methods. Relative to the winding, the need for the preparation of battery pole piece has certain flexibility, can ensure sheet when winding don't produce the problem such as brittle fracture, and metal materials, copper and aluminum foil and quality of a material soft metal. Finally is consider battery preparation cost, relatively speaking, copper foil price is relatively cheap, copper and aluminum in the world is rich in resources.

Second, the copper foil was relatively stable in the air. Aluminium is easy to react with oxygen in the air, and the oxide film was prepared on aluminum surface, to prevent further reaction of aluminium, and this very thin layer of oxide film of aluminum in the electrolyte has certain protective effect. Copper in itself is relatively stable in the air, little or no response in the dry air.

Third, it is lithium battery anode potential is decided to the anode aluminum foil, the cathode copper foil, not the other way round. The anode potential is high, the copper foil is easy to oxidation under high voltage, high oxidation potential, and aluminum and the aluminum foil surface layer and the oxide film has, also has good protection for the internal aluminum.

2, Current collector category and preparation process

Types of copper foil

According to the copper foil preparation methods, mainly has rolled copper foil and electrolytic copper foil. Battery invented in the early, due to restrictions, such as copper foil fabrication equipment technology mainly use the high cost of rolled copper foil, rolled copper foil (Rolled Copper Foil) is made of copper plate after repeating the roll and the original foil (also called MAO foil), according to the requirement of coarsening processing.

Rolled copper foil

Solution of copper foil (Electrode Posited copper) is the copper made by dissolving solution first, then in special electrolytic equipment, copper sulfate electrolyte under the effect of direct current (dc), electrode position and made the original foil, then according to the requirements of the original foil layer surface treatment and heat treatment and anti-oxidation and so on a series of surface treatment. Both sides electrolytic copper foil, unlike rolled copper foil, electrolytic copper foil surface crystal morphology, close to the cathode roller side is smooth, is called smooth; The other side in concave and convex shape, crystal structure of the rough, known as the wool surface.

Electrolytic copper foil

Copper foil fabrication process

(1) Rolled copper foil preparation process

Rolled copper foil is copper after many repeated roll, to a certain temperature and annealing and pickling of rolling over and over again. Copper foil rolling process parameters are controlled strictly, has a high requirement on the equipment and process control, at present mainly in the production in Japan, a small amount of used in lithium batteries.

(2) The electrolytic copper foil preparation process

Electrolytic copper foil is made solution dissolve copper, copper sulfate electrolyte in tailor-made solution container under the effect of direct current (dc), electrode position and made the original foil, then according to the requirements of the original foil layer surface treatment and heat treatment and anti-oxidation and so on a series of surface treatment.

Be compared and rolled copper foil, electrolytic copper foil preparation is relatively simple, relatively simple equipment requirements, cost is relatively low. Most of the copper foil for lithium ion batteries uses electrolytic copper foil as a negative electrode substrate.

Electrolytic copper foil in the process of preparation, due to the copper foil is depend on the copper electrolyte in electrolytic on titanium roll of foil and copper foil in titanium close to the roll surface is smooth, called smooth; The other side is the crystallization of uneven surface, which is relatively rough, called hair surface.

In the preparation process of the electrolytic copper foil, it is necessary to control the electrolyte temperature, the electrolyte concentration, the additive content, and the flow rate of the electrolyte at the time of raw foil. For electrolytic copper foil for lithium battery, the factors controlled in the pre-foil process will affect the purity, thickness/weight uniformity, strength and elongation of the copper foil itself. After electrolysis produce electrolytic copper foil thickness generally is the thickness of the manufacturer is needed, the late need to clean the surface of copper foil, removal of surface residual electrolyte, surface oxidation treatment and drying process. In this process, the degree of surface treatment directly affects the surface finish of the copper foil and the tension of the copper foil surface. After surface treatment need to conform to the requirements of the li-ion battery with copper foil coating, too smooth coating effect is poor, too rough has influence to the battery performance uniformity, at the same time, after the surface treatment of the surface tension of the copper foil for late copper foil cutting efficiency and battery preparation process plays a very important role.

After the completion of the copper foil surface treatment requires cutting, cutting into need the width and length of lithium-ion battery manufacturer. For the extensive use of copper foil substrate manufacturers, hope to suitable for copper foil width, the length of the copper foil in the range of portable length as long as possible, so that we can improve the efficiency of mass production, reduce the production cost. But at the moment due to foil equipment and cutting equipment, etc, the influence of the length of the copper foil is generally within the range of 2500 m.

Aluminum foil type

Aluminum foil is mainly prepared by rolling method. The classification method is mainly classified according to the type and content of impurities. The aluminum foil for lithium battery mainly has 1 series, 3 series and 8 series aluminum foil, which are industrial pure aluminum, aluminum manganese and aluminum and other common elements.

Technological process of preparation of aluminium foil

Aluminum foil production mainly through will be after a lot of rolling aluminum foil sheet rolled into the thickness of the need to heat treatment for many times. In this process are mainly roughing and finishing process, after finishing on aluminum foil surface treatment, the manufacturer of aluminum foil cutting into lithium electricity needs width and length, also need good control of aluminum foil in the process of tension.

Lithium battery with aluminum foil manufacturers commonly use rolling aluminum ingots upstream suppliers, so the composition of aluminum ingots basic is set, the late strength elongation requirements of aluminum foil is controlled by control rolling pressure and heat treatment process.

3, Main supplier of current collector

Copper foil

With the continuous development of electronic products, the global dependence on lithium batteries more and more intense, the demand for lithium ion battery material also more and more, then bring more material supplier. The cathode copper foil collector, suppliers also gradually from abroad to domestic. Copper foil for global suppliers are mainly distributed in Asia, with Japan's Mitsui Metals, Japan Energy, Furukawa Electric, Fukuda Metal and Nikko Materials in Japan, as well as Japan's largest manufacturer, Rijin, and Taiwan's Changchun Copper Foil and South Asia Plastics. The world's largest copper foil factory is Mitsui Metals, which is distributed throughout Japan, Taiwan, the United States, France and Malaysia.

China's domestic suppliers mainly include Shanghai Jinbao, Guangdong Meiyan Electrolytic Copper Foil, Lingbao Huaxin Copper Foil, Zhongke Yinghua High Technology, Huizhou United Copper Foil and other small manufacturers, mainly producing electrolytic copper foil.

Domestic copper foil production was relatively low, generally can't fully meet the needs of the lithium battery manufacturers, need to import some products from abroad, but also lack of high-end domestic copper foil, such as high strength and high toughness, ultra-thin copper foil.

The aluminum foil

There are relatively few suppliers of aluminum foil. There are mainly suppliers such as Fulaishun, Hangzhou Wuxing, Huaxi Aluminum, Nannan Aluminum, Sifangda, Zhongnan Aluminum, Shanghai Alcoa and Shenzhen Zhenxin Foil Electronic Packaging Materials.

Abroad is mainly in Japan, mainly in Japan's Oriental aluminum and Hitachi metals, etc.

4, some special collection of fluid

Special collection of fluid is mainly aimed at special requirements for performance of lithium battery, or is the future in order to develop higher performance materials collection of fluid.

Recently have relevant experts have "no negative cell", is actually imagine the cathode copper foil is replaced by metal lithium, lithium and layer is thin; at the same time, there are experts with cheap iron instead of high copper prices. But soon after the information released into question: from the point of lithium layer, the iron foil material itself, performance can't satisfy the lithium-ion batteries that need high performance, from the point of manufacturing process and equipment, it is difficult to meet the production, the final cost is basic it is difficult to solve. However, some R&D teams do not use other materials to replace the copper foil of the negative electrode substrate, but proceed from the copper foil itself to treat it to improve performance and optimize the performance of the lithium battery. The most intuitive is to develop high-strength and high-elongation copper foil with copper foil suppliers and develop thinner copper foil to increase battery energy density. In addition, copper mesh is used to increase battery energy density.

For aluminum foil, the existing aluminum foil is mainly subjected to surface treatment such as roughening treatment, cleaning treatment, or coating of conductive carbon on the surface of the aluminum foil. Recently, more research has been done on carbon coated aluminum foil, which is coated with a thin layer of conductive carbon on the surface of normal aluminum foil to optimize battery performance.

The page contains the contents of the machine translation.