KR20200056206A - Anode with high capacity, Method of making the same, and Lithium secondary battery comprising the same - Google Patents

Abstract

The present invention provides a method of manufacturing an negative electrode for a lithium secondary battery, and an negative electrode for a lithium secondary battery manufactured thereby, the method comprising the steps of: (S1) preparing a negative electrode current collector; (S2) preparing a spray composition containing a first conductive material, a dispersant, a binder, and negative electrode active material particles; (S3) preparing a spinning composition containing a third dispersant and a second conductive material; (S4) spraying the spray composition on the negative electrode current collector to form a negative electrode active material layer; and (S5) spinning the spinning composition on the negative electrode active material layer. In the negative electrode for a lithium secondary battery, a conduction path is successfully ensured even when the volume of the negative electrode active material changes.

Description

Anode with high capacity, Method of making the same, and Lithium secondary battery comprising the same}

The present invention relates to a high-capacity negative electrode, a method for manufacturing the same, and a lithium secondary battery comprising the same.

Due to the rapid increase in the use of fossil fuels, the demand for the use of alternative or clean energy is increasing, and as a part, the most actively researched field is the field of power generation and electricity storage using electrochemical reactions.

At present, a representative example of an electrochemical device using such electrochemical energy is a secondary battery, and its use area is gradually expanding. In recent years, as technology development and demand for portable devices such as portable computers, portable telephones, and cameras have increased, the demand for secondary batteries as an energy source has rapidly increased, indicating high energy density and operating potential among such secondary batteries and showing cycle life Many studies have been conducted on this long and low self-discharge lithium secondary battery, and it has been commercialized and widely used.

Conventional secondary batteries have been attempted to manufacture secondary batteries having various capabilities such as high capacity, high power, long life, and fast charging due to their use for various purposes.

In connection with the production of high-capacity secondary batteries, active materials having a high capacity, such as Si-based compounds, have a higher energy density than carbon-based negative active materials, such as graphite, and thus, have been spotlighted as the next-generation anode material. However, such a high-capacity negative electrode active material loses a conductive network due to volume change during charging and discharging, and thus it is difficult to guarantee performance in the long term.

Accordingly, attempts have been made to reduce the volume change rate by adjusting the working range of the high-capacity negative electrode active material, but this is not desirable because it is to reduce the capacity use rate. In addition, there is an aspect in which two types of conductive materials or flexible conductive materials are used, but if an excessive amount of conductive material is not used, it is difficult to adapt to the volume change rate of the high-capacity negative electrode active material. In addition, there have been attempts to suppress the volume expansion by adjusting the stiffness of the binder, but there is a problem that the binder loses elasticity and rapid deterioration occurs during the cycle.

Accordingly, the present invention is to solve the above problems, one object to be achieved in the present invention is to provide a negative electrode for a lithium secondary battery and a method for manufacturing the same, which can maintain an excellent conductive network even when the volume of the negative electrode active material particles is changed will be.

Another object of the present invention is to provide a negative electrode for a lithium secondary battery and a lithium secondary battery comprising the same.

According to a first aspect of the invention, the current collector; A negative electrode active material layer formed on the negative electrode current collector and including a negative electrode active material particle, a dispersant, and a binder having a first conductive material attached to the surface; And on the negative electrode active material layer is provided a negative electrode for a lithium secondary battery comprising a web structure layer formed of a fibrous conductive fiber formed from a second conductive material and a third dispersant.

According to a second aspect of the present invention, there is provided a negative electrode for a lithium secondary battery, which contains 0.6 to 2.5 parts by weight of a dispersant among 100 parts by weight of components constituting the negative electrode active material layer.

According to a third aspect of the present invention, in the first aspect or the second aspect, there is provided a negative electrode for a lithium secondary battery, which is composed of a (n + 1) layer of a negative electrode active material layer and a web structure layer formed of n layers of fibrous conductive fibers. do.

According to a fourth aspect of the present invention, there is provided a negative electrode for a lithium secondary battery, wherein the negative electrode active material includes a Si-based negative electrode active material in any one of the first to third aspects.

According to the fifth aspect of the present invention, in the aspect of any one of the first to fourth aspects, the conductive fiber web structure layer has a lithium secondary weight of 15 to 25 parts by weight based on 100 parts by weight of the negative electrode loading A negative electrode for a battery is provided.

According to a sixth aspect of the present invention, there is provided a negative electrode for a lithium secondary battery having a diameter of a fiber constituting the conductive fiber web structure layer in a range of 1 to 50 nm in any one of the first to fifth aspects.

According to a seventh aspect of the present invention, in a lithium secondary battery comprising a negative electrode, a positive electrode, and a separator interposed between the negative electrode and the positive electrode, the negative electrode according to any one of the first to sixth aspects A lithium secondary battery, which is a negative electrode for a lithium secondary battery, is provided.

According to an eighth aspect of the present invention, a method of manufacturing a negative electrode for a lithium secondary battery, comprising: (S1) preparing a negative electrode current collector; (S2) preparing a spray composition comprising a first conductive material, a dispersant, a binder, and negative electrode active material particles; (S3) preparing a spinning composition comprising a second conductive material and a third dispersant; (S4) spraying the spray composition on the negative electrode current collector to form a negative electrode active material layer; And (S5) spinning the radiation composition on the negative electrode active material layer. A method of manufacturing a negative electrode for a lithium secondary battery according to any one of the first to seventh aspects is provided.

According to a ninth aspect of the present invention, by the step (S4), the negative electrode active material particles, the dispersant and the binder to which the first conductive material is attached to the surface form droplets to form a negative electrode active material layer. A method of manufacturing a negative electrode for a secondary battery is provided.

According to a tenth aspect of the present invention, in the eighth or ninth aspect, a method of manufacturing a negative electrode for a lithium secondary battery is provided in which the negative electrode active material layer is not subjected to a drying process in step (S5).

The negative electrode for a lithium secondary battery according to the present invention has a conductive material attached to the negative electrode active material particle itself, and separately, a three-dimensional web structure formed of a fibrous conductive fiber is provided above and / or below the negative electrode active material layer.

As a result, in the negative electrode for a lithium secondary battery according to the present invention, even if a volume change occurs in the negative electrode active material particles, it is possible to maintain a continuous conductive network, and ultimately, charging and discharging characteristics of the lithium secondary battery including the negative electrode may be improved. have.

1 schematically illustrates a negative electrode for a lithium secondary battery formed by alternately stacking a negative electrode active material layer and a web structure layer formed of a conductive fiber according to an aspect of the present invention.

Hereinafter, the present invention will be described in more detail to aid understanding of the present invention.

The terms or words used in the present specification and claims should not be interpreted as being limited to ordinary or dictionary meanings, and the inventor can appropriately define the concept of terms in order to best describe his or her invention. Based on the principle that it should be interpreted as meanings and concepts consistent with the technical spirit of the present invention.

The terminology used herein is only used to describe exemplary embodiments, and is not intended to limit the present invention. Singular expressions include plural expressions unless the context clearly indicates otherwise.

In this specification, the terms "comprises", "haves" or "have" are intended to indicate the presence of implemented features, numbers, steps, elements or combinations thereof, one or more other features or It should be understood that the existence or addition possibilities of numbers, steps, elements, or combinations thereof are not excluded in advance.

In this specification, the 'active material layer' may be included as one or more layers in one electrode, and in particular, an active material layer formed between a current collector and a web structure layer formed of a fibrous conductive fiber, or a web structure layer formed of a fibrous conductive fiber It can be understood to refer to each of the active material layers formed between another web structure layer formed of a fibrous conductive fiber.

The present invention relates to a negative electrode for a lithium secondary battery, wherein the negative electrode for a lithium secondary battery comprises a current collector; A negative electrode active material layer formed on the negative electrode current collector and including a negative electrode active material particle, a dispersant, and a binder having a first conductive material attached to the surface; And a web structure layer formed on the negative electrode active material layer and formed of a fibrous conductive fiber formed from a second conductive material and a third dispersant.

Looking at the structure of the negative electrode for a lithium secondary battery of an embodiment of the present invention with reference to Figure 1, the current collector 10; A negative electrode active material layer 20a formed on the negative electrode current collector and including negative electrode active material particles having a first conductive material attached to the surface; And a web structure layer 30a formed on the anode active material layer and formed of a fibrous conductive fiber formed from a second conductive material and a third dispersant. A negative electrode active material layer 20b formed on the web structure layer 30b; A web structure layer 30b formed of a fibrous conductive fiber formed on the negative electrode active material layer 20b; And a negative electrode active material layer 20b formed on the web structure layer 30b.

The negative electrode current collector is not particularly limited as long as it has conductivity without causing a chemical change in the battery, and non-limiting examples of the negative electrode current collector include copper, gold, nickel or copper alloys, or foils produced by combinations thereof. There is this. The thickness of the negative electrode current collector is not particularly limited, but may have a thickness of 3 to 50 μm, which is usually applied.

The negative active material may be a high capacity negative active material, for example, a negative active material having an energy density of 500 mAh / g or more. Examples of the negative electrode active material include, but are not limited to, Si-based compounds, and more specifically, Si, Si-C, or mixtures thereof.

The negative active material may include other Si-containing materials in addition to the Si-based negative active material, such as SiO, SiO 2 or mixtures thereof; Sn-based materials such as Sn, SnO, and SnO ₂ ; Carbon-based materials such as artificial graphite, natural graphite, amorphous hard carbon, and low crystalline soft carbon; And it may further include a mixture of one or two or more selected from the group consisting of metal composite oxides such as lithium titanium oxide.

The negative active material may constitute a range of 50 to 85% by weight or 65 to 80% by weight of the total weight of the negative electrode active material layer. When the negative electrode active material is used in the negative electrode active material layer in the above range, the desired negative electrode capacity can be achieved while realizing the desired conductive network.

The negative active material may be in the form of particles having a D50 average particle diameter of 0.8 to 10 μm, a D50 average particle diameter of 1 to 8 μm, or a D50 average particle diameter of 2 to 7 μm. When the negative electrode active material particles have a D50 average particle diameter in the above numerical range, compared to the negative electrode active material having a larger or smaller D50 average particle diameter, even when the same amount of conductive material is used, there is an advantage in terms of forming a conductive network.

In the present specification, the term 'D50 average particle diameter' is a representative diameter of particles having two or more types of particle diameters, and a particle diameter corresponding to 50% of the weight percentage in the particle size distribution curve, that is, 50% of the cumulative weight in the particle size distribution curve passes It refers to the diameter of a particle, and is understood as the same meaning as the diameter of a particle corresponding to the size of a sieve that has passed 50% in total.

The average particle diameter of the negative electrode active material particles can generally be measured using a particle size analyzer or an electron microscope (SEM, TEM).

A first conductive material is attached to the surface of the negative electrode active material particle. Here, the term “adherence” between the negative electrode active material particle and the first conductive material is a covalent bond between the negative electrode active material particle and the first conductive material when the first conductive material is physically bound to the surface of the negative electrode active material particle by a binder and / or a dispersant. When this occurs and the first conductive material is attached to the negative electrode active material particle, when the first conductive material is bonded to the surface of the negative electrode active material particle by van der Waals force, when the first conductive material is physically bonded to the uneven surface of the negative electrode active material particle surface It is a concept that includes.

The first conductive material is not particularly limited as long as it is attached to the surface of the negative electrode active material particle to improve conductivity. For example, a carbon-based conductive material or a metal conductive material may be used, and preferably a carbon-based conductive material may be used.

Carbon-based conductive materials that can be used as the first conductive material include carbon nanotube (CNT), vapor-grown carbon fiber (VGCF), carbon nanofiber (CNF), and activated carbon. ), Graphite, graphene, graphene oxide (GO), reduced graphene oxide (RGO), carbon fiber, conductive polymer, It may be selected from the group consisting of aerogel (aerogel) and a mixture thereof, but is not limited thereto.

The carbon-based conductive material usable as the first conductive material is preferably a 'needle' or a 'flake'-shaped conductive material, preferably the first conductive material is in the range of 1:20 to 1: 500 or It may have an average aspect ratio of 1:50 to 1: 200. Further, the first conductive material may have a length in the range of 2 to 50 μm or 5 to 20 μm in the longest length. When the first conductive material has the above-described form, it can be attached to the negative electrode active material particles to improve the conductive path more effectively.

The term 'aspect ratio' in the present specification means a ratio of the longest dimension to the shortest dimension when projecting a conductive material into two-dimensional particles. In addition, the term 'average aspect ratio' means a number-weighted mean average of the aspect ratios of each conductive material in the conductive material population.

When 30 to 70 parts by weight of the negative electrode active material particles are used in 100 parts by weight of the components constituting the negative electrode active material layer, the first conductive material is included in a range of 3 to 15 parts by weight, preferably 5 to 10 parts by weight, and the negative electrode active material It may be included in the negative electrode active material layer attached to the particle surface. When the first conductive material is included in the above range, the conductivity of the negative electrode active material particles can be improved while preventing the loss of the negative electrode capacity.

The binder can help the first conductive material to adhere to the surface of the negative electrode active material particle, and also enables binding between the negative electrode active material particle and the negative electrode active material particle and the adjacent layer.

Non-limiting examples of binders that can be used include polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidenefluoride (PVDF), polyacrylonitrile, polymethyl One or two selected from the group consisting of methacrylate, polyvinyl alcohol, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, polyacrylic acid, acrylic copolymer and styrene butadiene rubber (SBR) It may include the above.

When 30 to 70 parts by weight of the negative electrode active material particles are used among 100 parts by weight of the components constituting the negative electrode active material layer, the binder may be included in the negative electrode active material layer in a range of 3 to 15 parts by weight, preferably 4 to 8 parts by weight. . When the binder is included in the above range, the binding between the negative electrode active material particles and the negative electrode active material particles and the adjacent layer can be preferably achieved while minimizing the action on resistance.

The dispersing agent constituting the negative electrode active material layer is, depending on the manufacturing process used, for example, when the spray composition is formed by mixing the first conductive material dispersion and the active material particle dispersion, the first dispersing agent used in the first conductive material dispersion It can be classified as a second dispersant used in the active material particle dispersion. Each of the first dispersant and the second dispersant is independently carboxymethyl cellulose (CMC), carboxyethyl cellulose, starch, regenerated carboxy methyl cellulose, ethyl cellulose, hydroxymethyl cellulose, hydroxyethyl Cellulose and hydroxypropyl cellulose, but may be one or a mixture of two or more selected from the group consisting of, but is not limited thereto.

When 30 to 70 parts by weight of the negative electrode active material particles are used in 100 parts by weight of the components constituting the negative electrode active material layer, the sum of the first dispersant and the second dispersant is 0.6 to 2.5 parts by weight, preferably 0.8 to 2.3 parts by weight Range. When the dispersant is included in the above range, the first conductive material can be uniformly attached to the surface of the negative electrode active material particle, and the action as a resistance can be minimized.

The negative electrode active material layer included between the current collector and the conductive fiber web structure layer or between the two layers of conductive fiber web structure layers has a loading in the range of 30 to 230 mg / 25 cm ² or 50 to 200 mg / 25 cm ² You can. When the negative electrode active material layer is configured to have a loading amount in the above range, the desired negative electrode capacity can be achieved while realizing the desired conductive network.

In the negative electrode for a lithium secondary battery of the present invention, on the negative electrode active material layer, a web structure layer formed of fibrous conductive fibers formed from a second conductive material and a third dispersant is formed.

Since the second conductive material has a purpose of improving the conductivity between the active material particles, rather than the surface of the active material particles, unlike the first conductive material, it is preferable to use particles equal to or larger than the first conductive material or long fibers. To this end, in the present invention, a second conductive material is formed in the form of a conductive fiber and a web structure formed of these conductive fibers is provided on the negative electrode active material layer.

The second conductive material may be the same as or different from the first conductive material, and examples of non-limiting examples include carbon black, carbon nano tube (CNT), and vapor-grown carbon fiber. VGCF), carbon nanofiber (CNF), activated carbon, graphite, graphene, graphene oxide (GO), reduced graphene oxide, RGO), a carbon fiber (conducting polymer) and a conductive polymer (conducting polymer), one or two or more mixtures selected from the group consisting of aerogels can be used.

Since the second conductive material should be formed of fibers having a diameter of 1 to 50 nm or preferably 2 to 30 nm, as described later, if it can be formed of fibers of the diameter, the size and shape Is not particularly limited.

The second conductive material may be bound by a third dispersant to form a fibrous web structure formed of conductive fibers.

The third dispersant may be the same as or different from the first dispersant and / or the second dispersant. For example, the third dispersant is independently carboxymethyl cellulose (CMC), carboxyethyl cellulose, starch, regenerated carboxy methyl cellulose, ethyl cellulose, hydroxymethyl cellulose, hydroxyethyl cellulose and It may be one or a mixture of two or more selected from the group consisting of hydroxypropyl cellulose, but is not limited thereto.

Further, the fibers constituting the conductive fiber web structure layer preferably have a diameter in the range of 1 to 50 nm, preferably 2 to 30 nm. When the fiber has a diameter in the above range, it is possible to impart conductivity between the particles of the negative electrode active material while having structural flexibility to facilitate contact with the active material particles.

The conductive fiber web structure layer preferably has a basis weight in the range of 15 to 25 parts by weight with respect to 100 parts by weight of the loading amount of the negative electrode active material for a lithium secondary battery. When the conductive fiber web structure layer has a basis weight in the above range, a significant improvement in conductivity can be achieved while preventing capacity loss of the negative electrode.

In one embodiment of the invention, the current collector; A negative electrode active material layer formed on the negative electrode current collector and including a negative electrode active material particle, a binder, and a dispersant having a first conductive material attached to the surface; And a conductive fiber web structure layer formed on the negative electrode active material layer and formed of a fibrous conductive fiber formed from a second conductive material and a third dispersant. In addition, the negative electrode active material layer and the conductive fiber web structure layer are alternately further It may be provided.

That is, in the negative electrode according to an aspect of the present invention, the negative electrode active material layer and the web structure layer formed of the fibrous conductive fiber are arranged in an alternating manner, and one or more of the negative electrode active material layer and the conductive fiber web structure layer It may be formed of more than one layer.

In addition, in the negative electrode according to an aspect of the present invention, each of the negative electrode active material layer and the web structure layer formed of the conductive fiber is formed of the same number of layers or is formed of the (n + 1) negative electrode active material layer and the n layer of fibrous conductive fibers. It can be made of a web structure layer. For example, the negative electrode according to an embodiment of the present invention may be composed of a current collector / cathode active material layer / conductive fiber web structure layer / cathode active material layer / conductive fiber web structure layer.

In the present invention, a method for manufacturing the negative electrode for a lithium secondary battery is provided.

The manufacturing method of the negative electrode for a lithium secondary battery includes (S1) preparing a negative electrode current collector; (S2) preparing a spray composition comprising a first conductive material, a binder, and negative electrode active material particles; (S3) preparing a spinning composition comprising a second conductive material and a third dispersant; (S4) spraying the spray composition on the negative electrode current collector to form a negative electrode active material layer; And (S5) spinning the radiation composition on the negative active material layer.

A method of manufacturing a negative electrode for a lithium secondary battery will be described in more detail below, and description of the content overlapping with the above-mentioned content in relation to the specific type and content of each component used will be omitted.

First, a negative electrode current collector is prepared (step (S1)).

In the present invention, the negative electrode current collector may be used as a grounded collector when the spray performed in a subsequent step is performed by electrospray and / or the radiation is performed by electric radiation. When the negative electrode current collector is used as a ground current collector plate, there is no need for a separate ground current collector plate, and it also has a process advantage of not having to transfer the product formed on the ground current collector plate to the negative electrode current collector. In addition, since the web structure is formed on the negative electrode current collector itself, a more solid bond between the web structure and the negative electrode current collector can be achieved, and since the negative electrode active material layer does not need to be transferred to the negative electrode current collector, the shape of the negative electrode active material layer is better preserved. There is an advantage.

Meanwhile, a spray composition comprising a first conductive material, a binder, and negative electrode active material particles is prepared (step (S2)).

The spray composition may be prepared prior to preparing the negative electrode current collector, prepared at the same time as preparing the negative electrode current collector, or may be provided after preparing the negative electrode current collector.

The spray composition is not particularly limited as long as it satisfies the object of the present invention, but in a non-limiting aspect, the first conductive material is dispersed in a dispersant solution (the 'first dispersant solution'). The process of preparing the re-dispersed liquid, the process of preparing the active material particle dispersion by adding the negative electrode active material particles and a binder to another dispersant solution ('second dispersant solution'), and the first conductive material dispersion and the active material particle dispersion Combination can be performed including a process.

More specifically, in order to prepare a dispersion of the first conductive material, a first dispersant is dissolved in a first solvent to prepare a first dispersant solution, and the first conductive material is introduced therein to disperse in a ball mill method. 1 Prepare a conductive material dispersion.

Further, in order to prepare a dispersion of negative electrode active material particles, a second dispersant is dissolved in a second solvent to prepare a second dispersant solution, and the negative active material particles are added thereto to be mixed and dispersed through a planetary mixer. After, the binder is post-added. After the negative electrode active material particles are introduced into the second dispersant solution and mixed, the binder may be post-added to have an effect of maintaining the shape of the binder.

The first solvent and the second solvent may be the same or different, and each independently selected from the group consisting of water, methanol, ethanol and N-methyl-pyrrolidone (N-methyl-2-pyrrolidone) or 2 Mixtures of more than one species can be used.

In one embodiment of the present invention, the first dispersant and the second dispersant used in each of the first conductive material dispersion and the negative electrode active material particle dispersion may be compounds of the same type and having different weight average molecular weights. Preferably, as a first dispersant in the first conductive material dispersion, a compound having a weight average molecular weight in the range of 50,000 to 500,000 in the case of low molecular weight, preferably carboxy methyl carboxy methyl cellulose (CMC), is selected. As the second dispersant, a compound having a weight average molecular weight in the range of 700,000 to 1.8 million may be used in the case of a medium molecular weight, preferably carboxy methyl carboxy methyl cellulose (CMC). Accordingly, it is possible to have an effect of securing dispersibility of inorganic particles of different shapes and sizes.

Each of the first dispersant solution and the second dispersant solution is preferably prepared by adding 0.3 to 1.0 parts by weight of the dispersant based on 100 parts by weight of the solvent to achieve uniform dispersion of the subsequently charged material.

The first conductive material dispersion obtained from the above and the negative electrode active material particle dispersion are combined to obtain a spray composition, wherein the spray composition is 30 to 70 parts by weight of the negative electrode active material particles and 3 to 1 part of the first conductive material It is preferable to include 20 parts by weight, 3 to 15 parts by weight of the binder, and 0.6 to 2.5 parts by weight of the dispersant. When the spray composition is manufactured with such a composition, the first conductive material can be attached to the surface of the negative electrode active material particles, and aggregation between the active material particles or aggregation between the conductive material particles can be minimized. The first conductive material dispersion and the negative electrode active material particle dispersion may be used in a weight ratio of 15:85 to 30:70.

When preparing the first conductive material dispersion and the negative electrode active material particle dispersion, mixing may be performed so that each component is better dispersed. The mixing may be performed in a conventional manner made in the art, and includes, but is not limited to, a homo mixer, an ultrasonic disperser (Ultrasonic), a homogenizer (Homogenizer), a planetary mixer and a bead mill (bead mill) selected from the group consisting of 1 It may be performed using a species or more, but is not limited thereto.

However, in the case of using a binder in the form of a water-dispersion emulsion particle as a binder, there is a possibility that agglomeration or breakage of the binder particles occurs in the dispersion process, and thus, it is added after the dispersion process for adding and dispersing the active material particles to the dispersion liquid. It is preferred to carry out mixing in a stirrer which is stirred at a low shear rate, preferably in the range of 10 to 60 rpm.

According to the present invention, when the negative electrode active material particle dispersion is sprayed, only a small amount or a small amount of solvent is present in the injected negative electrode active material particles, and thus migration of the binder generated in the process of drying the solvent or dispersion medium of the active material slurry ) May not occur or may be minimized. In addition, it has a process advantage that can save time, equipment and cost for drying.

Subsequently, a spinning composition containing a second conductive material and a third dispersant is prepared (step S3).

More specifically, the spinning composition is prepared by dissolving a third dispersant in a third solvent to obtain a third dispersant solution, and dispersing a second conductive material in the third dispersant solution to prepare a spinning composition.

The third solvent used in the preparation of the spinning composition may be one, or a mixture of two or more selected from the group consisting of water, methanol, ethanol and N-methyl-pyrrolidone (N-methyl-2-pyrrolidone). The third solvent may be the same or different from the first solvent and / or the second solvent used in the spinning composition, and is preferably the same as the first solvent and the second solvent.

5 to 50 parts by weight or 7 to 35 parts by weight of the second conductive material and 0.5 to 5 parts by weight of the third dispersant or 0.8 to 4 parts by weight based on 100 parts by weight of the third solvent may be used to form a spinning composition. When the spinning composition is formed with the above composition, while having a viscosity suitable for spinning, aggregation between particles of the conductive material may be minimized.

The mixing may be performed in a conventional manner made in the art, and includes, but is not limited to, one or more selected from the group consisting of a homo mixer, an ultrasonic disperser (Ultrasonic), a homogenizer (Homogenizer) and a bead mill (bead mill). It may be performed using, but is not limited to.

Subsequently, the negative electrode active material layer is formed by spraying the spray composition on the negative electrode current collector (step S4).

When the spray composition is sprayed to the current collector by electrospraying, the active material particles and the binder to which the first conductive material dispersed in the spray composition is attached are sprayed onto the surface of the current collector to be adhered in the form of droplets and droplets. (spray). Since the small droplets are not greatly affected by gravity, the negative electrode active material layer can be immediately and uniformly formed without aggregation.

In order to perform the electrospray, it is necessary to consider the thickness of the negative electrode active material layer, the area to be sprayed, the viscosity of the spray composition, the applied voltage, the distance between the nozzle and the substrate, the spray speed and the spray amount of the spray composition.

Non-limitingly, the applied voltage for electrospray is preferably a high voltage, specifically in the range of 0.1 to 20 kV, preferably about 15 kV. At this time, if the applied voltage is less than 0.1 kV, it may be difficult to obtain a uniform film because the dispersion of the spray composition particles is difficult, and, conversely, when it exceeds 20 kV, the angle of the spray composition to be sprayed increases, thereby reducing the deposition efficiency and loss of the spray composition. This will grow.

The distance between the electrospray nozzle and the substrate, that is, the current collector is preferably 10 to 50 cm, which can be determined in consideration of the applied voltage. If the distance (D) between the nozzle and the substrate is less than 10 cm, the process change for the unevenness of the substrate is large. Conversely, when the distance D exceeds 50 cm, there may be a disadvantage that an applied voltage increases.

The electrospray may be performed under vacuum or atmospheric pressure.

According to one embodiment of the present invention, the spray composition may be sprayed onto the current collector even by general spraying.

When the negative electrode active material layer is formed by general spraying, the spray composition may be sprayed by an injection pressure in the range of 300 to 500 Pa. When the injection pressure is within the above range, the capacity and conductivity characteristics of the negative electrode active material are excellent.

Subsequently, the spinning composition is spun on the negative active material layer (step S5).

In order to improve adhesion properties between the negative electrode active material layer and the second conductive fiber web structure layer by spinning performed in step (S5), preferably, the spinning is completely drying the negative electrode active material layer generated in step (S4). It can be done in the previous state. Therefore, it is preferable to spin the spinning composition on the negative electrode active material layer immediately, without going through a separate drying process after the electrospray or general injection is performed.

The radiation may be electrospinning. The electrospinning is preferably performed in a voltage range of 10 to 30 kV, and a distance between the electrospinning nozzle and the current collector in a range of 5 to 20 cm. If it is outside the above range, it is difficult to form a nano-diameter fibrous conductive material or a web structure made of a fibrous conductive material can be easily destroyed in a drying process.

Subsequently, (S4) and (S5) may be repeated until the cathode capacity reaches a desired level to selectively achieve the purpose of more uniformly forming the conductive network in the electrode thickness direction ((S6). step).

In general, the thickness of the negative electrode active material layer formed through the steps (S4) and (S5) is 10 to 50 μm or 15 to 30 μm, and when the applied amount of the negative electrode active material does not reach the designed capacity (S4) and The negative electrode capacity can be achieved by repeatedly performing the step (S5) several times.

Subsequently, optionally, the negative electrode having the negative electrode active material layer formed from the above may be dried in a conventional manner in the art. The preferred drying temperature is 40 to 100 ° C, and the time required for drying may be 1 to 3 minutes. A small amount or a small amount of moisture contained in the negative electrode active material layer may be dried by such drying.

Then, the negative electrode obtained from above is rolled. Rolling may be performed in a manner conventional in the art within a range in which the web structure layer including the second conductive material is not destroyed, and a non-limiting example is a desired thickness by passing an electrode between two rolls whose temperature is controlled. Can be compressed into. As a specific example, rolling may be performed under a pressure of 10 MPa to 20 MPa between rolls controlled at 20 ° C to 90 ° C or 20 ° C to 25 ° C.

In the present invention, a negative electrode for a lithium secondary battery formed by the above manufacturing method is provided.

The lithium secondary battery of the present invention may be made of a positive electrode, a separator, and an electrolyte together with the negative electrode described above.

The positive electrode is a positive electrode current collector; And a positive electrode active material layer formed on the positive electrode current collector and including a positive electrode active material, a binder, and a conductive material. The positive electrode active material layer may further include additives commonly used in the art. .

The positive electrode current collector is not particularly limited as long as it has conductivity without causing a chemical change in the battery. For example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel Surfaces treated with carbon, nickel, titanium, silver, or the like may be used.

The positive electrode active material may be a layered compound such as lithium cobalt oxide (LiCoO ₂ ) or lithium nickel oxide (LiNiO ₂ ) or a compound substituted with one or more transition metals; Lithium manganese oxides such as the formula Li _{1 + y} Mn _{2 - y} O ₄ (where y is 0-0.33), LiMnO ₃ , LiMn ₂ O ₃ , LiMnO ₂ ; Lithium copper oxide (Li ₂ CuO ₂ ); Vanadium oxides such as LiV ₃ O ₈ , LiFe ₃ O ₄ , V ₂ O ₅ and Cu ₂ V ₂ O ₇ ; Ni site type lithium nickel oxide represented by the formula LiNi _1-y M _y O ₂ (where M = Co, Mn, Al, Cu, Fe, Mg, B or Ga, and y = 0.01-0.3); Formula LiMn _{2 - y} M _y O ₂ (where M = Co, Ni, Fe, Cr, Zn or Ta, y = 0.01-0.1) or Li ₂ Mn ₃ MO ₈ (where M = Fe, Co, Lithium manganese composite oxide represented by Ni, Cu or Zn); LiMn ₂ O _{4 in} which a part of Li in the formula is substituted with alkaline earth metal ions, and the like, are not limited thereto.

The binder used together with the positive electrode active material may be the same or different from the binder described above in relation to the negative electrode, and non-limiting examples include polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HEP) and polyvinyl. Polyvinylidenefluoride (PVDF), polyacrylonitrile, polymethylmethacrylate, polyvinyl alcohol, carboxymethylcarboxy methyl cellulose (CMC), starch, hydroxypropylcarboxy methyl cellulose, regenerated carboxy Methyl cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, polyacrylic acid, styrene butadiene rubber (SBR), and the like, but are not limited thereto.

The conductive material used with the positive electrode active material may be the same as or different from the first conductive material or the second conductive material described above in relation to the negative electrode, and includes, but is not limited to, carbon black, carbon nano tube. , CNT), vapor-grown carbon fiber (VGCF), carbon nanofiber (CNF), activated carbon, graphite, graphene, graphene, graphene oxide, GO), reduced graphene oxide (reduced graphene oxide, RGO), carbon fiber (carbon fiber) and conductive polymer (conducting polymer), may be a mixture of one or more selected from the group consisting of aerogel (aerogel) have.

The drying process is a process of removing the solvent in the slurry to dry the electrode slurry coated on the current collector. As a specific example, the drying may be performed within 1 day in a vacuum oven at 50 ° C to 200 ° C.

The separator separates the negative electrode from the positive electrode and provides a passage for lithium ions. If the separator is used as a separator in a secondary battery, it can be used without particular limitation. In particular, it has low resistance to ion migration of electrolyte and has excellent electrolyte moisture absorption ability. It is preferred. Specifically, porous polymer films such as ethylene homopolymers, propylene homopolymers, ethylene / butene copolymers, ethylene / hexene copolymers and polyolefin polymers such as ethylene / methacrylate copolymers or the like. A laminate structure of two or more layers of may be used. In addition, a conventional porous non-woven fabric, for example, a high-melting point glass fiber, a polyethylene terephthalate fiber or the like may be used. In addition, a coated separator containing a ceramic component or a polymer material may be used to secure heat resistance or mechanical strength, and may optionally be used in a single layer or multilayer structure.

Examples of the electrolyte include an organic liquid electrolyte, an inorganic liquid electrolyte, a solid polymer electrolyte, a gel polymer electrolyte, a solid inorganic electrolyte, and a molten inorganic electrolyte that can be used in the manufacture of a lithium secondary battery, but are not limited thereto.

Specifically, the electrolyte may include a non-aqueous organic solvent and a metal salt.

Examples of the non-aqueous organic solvent include, for example, N-methyl-2-pyrrolidinone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, gamma-butyl lactone, 1,2-dime Methoxyethane, 2-methyl tetrahydrofuran, dimethylsulfoxide, 1,3-dioxolane, formamide, dimethylformamide, dioxolane, acetonitrile, nitromethane, methyl formate, methyl acetate, phosphoric acid triester, trimethoxy Non-protonic organic solvents such as methane, dioxolane derivatives, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivatives, tetrahydrofuran derivatives, ethers, methyl pyropionate, ethyl propionate Can be used.

Particularly, among the carbonate-based organic solvents, ethylene carbonate and propylene carbonate, which are cyclic carbonates, are high-viscosity organic solvents and have high dielectric constants, and can be preferably used because they dissociate lithium salts well. Dimethyl carbonate and diethyl carbonate can be used in these cyclic carbonates. When the same low-viscosity and low-permittivity linear carbonate is mixed and used in an appropriate ratio, an electrolyte having a high electrical conductivity can be produced, and thus it can be more preferably used.

The metal salt may be a lithium salt, the lithium salt is a material that is readily soluble in the non-aqueous electrolyte, for example, is in the lithium salt anion ^{F -, Cl -, I -} , NO 3 -, N (CN _{^{) 2 -, BF 4 -,}} ClO 4 -, PF 6 -, (CF 3) 2 PF 4 -, (CF 3) 3 PF 3 -, (CF 3) 4 PF 2 -, (CF 3) 5 PF - ^{_{, (CF 3) 6 P -}} , CF 3 SO 3 -, CF 3 CF 2 SO 3 -, (CF 3 SO 2) 2 N -, (FSO 2) 2 N -, CF 3 CF 2 (CF 3) 2 _{^{CO -, (CF 3 SO 2}} ) 2 CH -, (SF 5) 3 C -, (CF 3 SO 2) 3 C -, CF 3 (CF 2) 7 SO 3 -, CF 3 CO 2 -, CH 3 CO ₂ ^-, SCN ^- may be used one selected from the group consisting of ^- and _{(CF 3 CF 2 SO 2)} 2 N.

In addition to the electrolyte components, the electrolyte includes haloalkylene carbonate-based compounds such as difluoro ethylene carbonate, pyridine, and tree for the purpose of improving the life characteristics of the battery, suppressing the decrease in battery capacity, and improving the discharge capacity of the battery. Ethylphosphite, triethanolamine, cyclic ether, ethylene diamine, n-glyme, hexaphosphate triamide, nitrobenzene derivative, sulfur, quinone imine dye, N-substitutedoxazolidinone, N, N-substituted imida One or more additives such as zolidine, ethylene glycol dialkyl ether, ammonium salt, pyrrole, 2-methoxy ethanol or aluminum trichloride may be further included.

The secondary battery is useful in portable devices such as mobile phones, notebook computers, digital cameras, and electric vehicle fields such as hybrid electric vehicles (HEV).

According to another embodiment of the present invention, a battery module including the secondary battery as a unit cell and a battery pack including the same are provided. The battery module or battery pack includes a power tool; An electric vehicle including an electric vehicle (EV), a hybrid electric vehicle, and a plug-in hybrid electric vehicle (PHEV); Alternatively, it can be used as a power supply for any one or more of medium and large devices in a power storage system.

Hereinafter, embodiments of the present invention will be described in detail so that those skilled in the art to which the present invention pertains can easily practice. However, the present invention can be implemented in many different forms and is not limited to the embodiments described herein.

Example  One

Preparation of cathode

Step 1: Preparation of spray composition and spinning composition

5 g of a low molecular weight carboxy methyl cellulose (CMC) (GC, SG-L02) powder having a weight average molecular weight of 100,000 was dissolved in 450 g of water at room temperature to prepare a CMC solution as a first dispersant solution. To this, 45 g of CNT (LG Chemical, B-CNT) was added as the first conductive material, followed by dispersion with a bead mill for 3 hours to prepare a first conductive material dispersion.

5 g of a medium-molecular weight CMC (GL Chem, BG-L01) powder having a weight average molecular weight of 780,000 was dissolved in 450 g of water at room temperature to prepare a CMC solution as a second dispersant solution. To this, 500 g of Si particles (Wacker) having an average diameter (D50) of 5 μm were added as negative electrode active material particles, and Si particles were dispersed by mixing at 450 rpm for 40 minutes using a Planetary mixer. Thereafter, 50 g of water-dispersing particles (Zeon, BM-L302), which is a mixture of an acrylic copolymer and styrene-butadiene, were added as a binder to prepare a negative electrode active material particle dispersion.

A spray composition was prepared by mixing the first conductive material dispersion and the negative electrode active material particle dispersion in a weight ratio of 2: 8.

Subsequently, 5 g of low molecular weight carboxy methyl cellulose (CMC) (GC, SG-L02) powder was dissolved in 450 g of water at room temperature to prepare a CMC solution as a third dispersant solution. After adding 45 g of CNT (LG Chemical, B-CNT) as the second conductive material, the composition was prepared by dispersing with a bead mill for 3 hours.

Step 2: Active material layer  And formation of conductive fiber web structures

The spray composition prepared above was electrically sprayed onto a copper foil having a thickness of 10 μm. At this time, the applied voltage applied to the electrospray device was 15 kV, and the distance between the copper foil and the nozzle to which the spray composition was injected was maintained at 15 cm. After the electrospraying was performed, instead of going through a separate drying process, the spinning composition prepared above was spun on the injected spray composition under the same conditions. This spraying and spinning process was repeated 5 times each, and then dried at 60 ° C. to form a structure having a total thickness of 75 μm consisting of a negative electrode active material layer and a conductive fiber web structure layer, and then rolled. The thickness after rolling was 67 µm.

Comparative example  One

When preparing the spray composition, a slurry was prepared in the same manner as in Example 1, except that the dispersant CMC was not used. When spraying through the nozzle to produce the spray composition, the nozzle was clogged due to agglomeration between particles, so that a normal cathode could not be produced.

Comparative example  2

The spray composition and the spinning composition prepared in Example 1 were prepared in the same manner as in Example 1, but they were mixed to prepare a single slurry. The prepared slurry was electrosprayed under the same conditions as in Example 1 to form a negative electrode active material layer having a total thickness of 75 μm, and then rolled. The thickness after rolling was 67 µm.

Comparative example  3

The single slurry prepared in Comparative Example 2 was formed into a negative electrode active material layer having a total thickness of 75 μm by a coating method, and then rolled. The thickness after rolling was 67 µm.

Experimental Example

Coin half cells were fabricated as cathodes prepared in Examples and Comparative Examples 2 and 3. The charge was charged to 1.0 C under CC / CV conditions, and when it reached 0.005 V, the current was lowered until it reached 0.005 C. The discharge was discharged at 1.0 C under CC conditions and ended at 1.5 V. The charge and discharge were repeatedly performed 25 times, disassembled, and the thickness of the cathode was measured, and compared with the thickness in the initial and post-activation stages.

Early After activation After 25 charges and discharges Example 1 67 μm 106 μm 116 μm Comparative Example 2 67 μm 107 μm 138 μm Comparative Example 3 67 μm 109 ㎛ 143 μm

From the above results, it can be seen that in the charging and discharging process, an increase in the thickness of the electrode occurs due to the volume expansion of the negative electrode active material, and in particular, in the comparative examples 2 and 3, in which the conductive network is not good, such increments are larger.

Claims (10)

Current collector;
A negative electrode active material layer formed on the negative electrode current collector and including a negative electrode active material particle, a dispersant, and a binder having a first conductive material attached to the surface; And
A web structure layer formed on the negative electrode active material layer and formed of a fibrous conductive fiber formed from a second conductive material and a third dispersant;
A negative electrode for a lithium secondary battery comprising a.
According to claim 1,
A method of manufacturing a negative electrode for a lithium secondary battery, which includes 0.6 to 2.5 parts by weight of a dispersant among 100 parts by weight of the components constituting the negative electrode active material layer.
According to claim 1,
The negative electrode for a lithium secondary battery, wherein the negative electrode for a lithium secondary battery consists of a (n + 1) layer of a negative electrode active material layer and a web structure layer formed of n layers of fibrous conductive fibers.
According to claim 1,
The negative electrode for a lithium secondary battery, wherein the negative active material includes a Si-based negative active material.
According to claim 1,
The negative electrode for a lithium secondary battery, wherein the conductive fiber web structure layer has a basis weight of 15 to 25 parts by weight based on 100 parts by weight of the negative electrode.
According to claim 1,
A negative electrode for a lithium secondary battery having a diameter of 1 to 50 nm in diameter of fibers constituting the conductive fiber web structure layer.
A lithium secondary battery comprising a negative electrode, a positive electrode, and a separator interposed between the negative electrode and the positive electrode, wherein the negative electrode is a negative electrode for a lithium secondary battery according to any one of claims 1 to 6.
As a method of manufacturing a negative electrode for a lithium secondary battery,
(S1) preparing a negative electrode current collector;
(S2) preparing a spray composition comprising a first conductive material, a dispersant, a binder, and negative electrode active material particles;
(S3) preparing a spinning composition comprising a third dispersant and a second conductive material;
(S4) spraying the spray composition on the negative electrode current collector to form a negative electrode active material layer; And
(S5) spinning the radiation composition on the negative electrode active material layer (spinning);
Method for producing a negative electrode for a lithium secondary battery according to claim 1 comprising a.
The method of claim 8,
By the (S4) step, the negative electrode active material particles, the dispersant and the binder to which the first conductive material is attached to the surface to form a droplet (droplet) to form a negative electrode active material layer is a method for manufacturing a negative electrode for a lithium secondary battery.
The method of claim 8,
The method of manufacturing a negative electrode for a lithium secondary battery, wherein the negative electrode active material layer is not subjected to a drying process in step (S5).

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