Pole piece, and electrochemical device and electronic device including the same

Abstract

The present invention relates to the field of energy storage technology, particularly to pole pieces and electrochemical and electronic devices including the same. The pole pieces of the present invention include a current collector and a film piece. The film piece includes an undercoat layer formed on the surface of the current collector and an active material layer formed on the surface of the undercoat layer, and the undercoat layer includes a first binder and a first conductive agent. The adhesive strength between the film piece and the current collector is ≥ 20 N / m. The present invention can alleviate problems in the prior art, such as the tendency for pole pieces to peel off due to low adhesive strength of the active material portion close to the surface of the current collector.

Description

Technical Field

[0001] The present invention claims the priority of a Chinese patent application filed with the Chinese Patent Office on October 15, 2020, with an application number of 202011104624.X and an invention title of "Electrode Tab, and Electrochemical Device and Electronic Device Containing the Same", the entire content of which is incorporated herein by reference.

[0002] The present invention relates to the field of energy storage technologies, and specifically to electrode tabs, and electrochemical devices and electronic devices containing the same, particularly lithium-ion batteries.

Background Art

[0003] With the development of technology and the increasing demand for mobile devices, the demand for electrochemical devices (such as lithium-ion batteries) has increased significantly. Lithium-ion batteries with high energy density, excellent lifespan and cycle characteristics are one of the research directions.

[0004] The positive and negative electrodes of lithium-ion batteries repeatedly insert and desorb lithium ions as the cycle progresses, and the volume of the active material expands and contracts as the lithium ions are inserted and desorbed. Here, the volume expansion and contraction of the negative electrode active material (such as graphite, silicon-based materials) are intense. In the prior art, the adhesion of the active material portion close to the surface of the negative electrode current collector is low, and as the volume of the active material expands or contracts during the cycle process, it is easy to cause the separation between the negative electrode active material layer close to the surface layer of the current collector and the surface of the current collector, resulting in the peeling of the electrode tab, and further leading to an increase in internal resistance and deterioration of cycle performance.

[0005] In recent years, researchers have been vigorously working on the development of silicon-based negative electrode materials to meet the needs of high energy density. Silicon-based negative electrode materials have a more intense volume change during the insertion and desorption process of lithium ions, and the peeling phenomenon due to the above volume change is more serious at the surface portion of the current collector.

[0006] In view of this situation, it is necessary to provide an improved electrochemical device having excellent cycle characteristics.

Summary of the Invention

[0007] An object of the present invention is to provide a current collector and a cathode plate having high adhesion that can solve at least some of the problems existing in the prior art to some extent, as well as an electrochemical device and an electronic device including the same.

[0008] According to a first aspect of the present invention, there is provided a cathode plate including a current collector and a film piece, wherein the film piece includes an undercoat layer provided on the surface of the current collector and an active material layer provided on the surface of the undercoat layer, and the undercoat layer includes a first binder and a first conductive agent. Here, the adhesion between the film piece and the current collector is ≧20 N / m.

[0009] Preferably, according to some embodiments of the present invention, the adhesion between the film piece and the current collector is ≧80 N / m, and more preferably, according to some embodiments of the present invention, the adhesion between the film piece and the current collector is ≧100 N / m, and more preferably, according to some embodiments of the present invention, the adhesion between the film piece and the current collector is ≧500 N / m.

[0010] According to some embodiments of the present invention, the thickness of the undercoat layer is 100 nm to 2 μm, preferably, according to some embodiments of the present invention, the thickness of the undercoat layer is 100 nm to 1000 nm, and more preferably, according to some embodiments of the present invention, the thickness of the undercoat layer is 100 nm to 800 nm.

[0011] According to some embodiments of the present invention, when the average particle diameter of the particles of the first conductive agent or the average diameter of the tubes is D and the thickness of the undercoat layer is H, the ratio D / H of D to H satisfies 0.25 to 1.5, preferably 0.5 to 1.25.

[0012] According to some embodiments of the present invention, the compression density of the film piece is 1.30 g / cm 3 ~1.80 g / cm 3 .

[0013] According to some embodiments of the present invention, the porosity of the film piece is 20% to 50%. Preferably, according to some embodiments of the present invention, the porosity of the film piece is 25% to 40%.

[0014] According to some embodiments of the present invention, the Electrode resistance is 3 mΩ to 50 mΩ. Preferably, according to some embodiments of the present invention, the Electrode resistance is 3 mΩ to 30 mΩ.

[0015] According to some embodiments of the present invention, the mass content of the first binder in the undercoat layer is 20% to 95%.

[0016] According to some embodiments of the present invention, the mass content of the first conductive agent in the undercoat layer is 5% to 80%.

[0017] According to some embodiments of the present invention, the first binder may include at least one of a carbon-carbon double bond, a carboxyl group, a carbonyl group, a carbon-nitrogen single bond, a hydroxyl group, an ester group, an acyl group, and an aryl group. Preferably, according to some embodiments of the present invention, the first binder may include at least one of a carboxyl group, a carbonyl group, a carbon-nitrogen single bond, a hydroxyl group, and an ester group functional group.

[0018] According to some embodiments of the present invention, the first binder may include at least one of SBR (styrene-butadiene rubber), PAA (polyacrylic acid), PVP (polyvinylpyrrolidone), and PAM (polyacrylamide).

[0019] According to some embodiments of the present invention, the first conductive agent may include at least one of conductive carbon black, Ketjen black, single-walled carbon nanotubes, and multi-walled carbon nanotubes.

[0020] According to some embodiments of the present invention, the active material layer includes an active material and a second binder.

[0021] According to some embodiments of the present invention, the active material may include at least one of graphite-based materials and silicon-based materials.

[0022] According to some embodiments of the present invention, the silicon-based material may include at least one of silicon, silicon oxide, silicon-carbon composite, and silicon alloy. Preferably, according to some embodiments of the present invention, the silicon-based material is pure silicon, SiO x (0 < x ≤ 2) and at least one of silicon-carbon composites.

[0023] According to some embodiments of the present invention, the active material layer further includes a second conductive agent.

[0024] According to some embodiments of the present invention, the active material layer includes, by mass content, 80% - 99% of the active material, 0.8% - 20% of the second binder, and 0 - 5% of the second conductive agent.

[0025] According to some embodiments of the present invention, the second binder may include at least one of PAA (polyacrylic acid), PVP (polyvinylpyrrolidone), PAM (polyacrylamide), SBR (styrene-butadiene rubber), and CMC (carboxymethyl cellulose).

[0026] According to some embodiments of the present invention, the second conductive agent may include at least one of conductive carbon black, Ketjen black, single-walled carbon nanotubes, and multi-walled carbon nanotubes.

[0027] According to a second aspect of the present invention, there is provided an electrochemical device including a positive electrode plate, a negative electrode plate, and a separator provided between the positive electrode plate and the negative electrode plate, wherein the negative electrode plate is the above-mentioned electrode plate.

[0028] According to some embodiments of the present invention, the electrochemical device includes an electrolytic solution, and the electrolytic solution includes a compound containing an S=O double bond.

[0029] According to some embodiments of the present invention, the compound containing an S=O double bond may include at least one of a cyclic sulfate, a chain sulfate, a chain sulfonate, a cyclic sulfonate, a chain sulfite, and a cyclic sulfite.

[0030] According to some embodiments of the present invention, the compound containing an S=O double bond may include at least one of the compounds represented by Formula 1.

[0031]

Chemical formula

Chemical formula

[0032] According to some embodiments of the present invention, the compound represented by Formula 1 is

Chemical formula

[0033] According to some embodiments of the present invention, when the mass fraction of the compound containing the S=O double bond in the electrolyte is y and the porosity of the film piece is V, y and V satisfy the relational expression 0.01 ≦ y / V ≦ 0.07.

[0034] According to a third aspect of the present invention, an electronic device including the electrochemical device is provided.

[0035] The technical solution of the present invention has at least the following beneficial effects.

[0036] The electrode sheet provided by the present invention, the electrochemical device and the electronic device including this electrode sheet improve the adhesion between the film sheet and the current collector by providing an undercoat layer on the film sheet of the electrode sheet, avoid peeling due to expansion and contraction during the cycling process of the electrode sheet, greatly improve the cycle and shape stability of the electrochemical device, and ensure that the electrochemical device has excellent rate characteristics. Other aspects and advantages of the embodiments of the present invention will be partially described, illustrated, or explained through the implementation of the embodiments of the present invention below.

Brief Description of the Drawings

[0037] Hereinafter, in order to describe the embodiments of the present invention, the necessary drawings for describing the embodiments of the present invention or the prior art will be briefly described. It is self-evident that the drawings described below are only a part of the embodiments of the present invention. For those skilled in the art, on the premise of not exerting creative efforts, it is still possible to obtain the drawings of other embodiments according to the structures illustrated in these drawings.

[0038]

Figure 1

Figure 2

Figure 3

Figure 4

[0039] Here, the description of the reference signs is as follows. 10 - negative electrode current collector; 20 - film piece; 201 - undercoat layer; 202 - active material layer.

Mode for Carrying Out the Invention

[0040] Hereinafter, embodiments of the present invention will be described in detail. The embodiments of the present invention should not be construed as limiting the present invention.

[0041] The following terms used in this specification have the meanings shown below unless otherwise specified.

[0042] In specific embodiments and claims, a list of terms connected by the terms "at least one of", "at least one of", "at least one kind of", or other similar terms means any combination of the listed terms. For example, when terms A and B are listed, the phrase "at least one of A and B" means only A, only B, or A and B. In another example, when terms A, B, and C are listed, the phrase "at least one of A, B, and C" means only A, only B, only C, A and B (excluding C), A and C (excluding B), B and C (excluding A), or all of A, B, and C. Term A may include a single element or a plurality of elements. Term B may include a single element or a plurality of elements. Term C may include a single element or a plurality of elements.

[0043] As used herein, the term "and / or" or " / " is merely a relationship describing the relevant objects, indicating that three relationships can exist. For example, A and / or B can indicate that A exists alone, both A and B exist, and B exists alone. Further, for ease of description, the terms "first", "second", and similar terms used herein do not indicate order, quantity, or importance, but are merely used to distinguish different elements.

[0044] In addition, in this specification, quantities, ratios, and other values may be expressed in ranges. Such ranges are for the purpose of convenience and brevity, and it should be understood that such ranges include not only the numerical values explicitly specified as limited values in the range, but also all the individual values and sub-ranges included within the said range, corresponding to the case where each value and sub-range is explicitly specified.

[0045] The electrodes (positive or negative electrodes) of an electrochemical device (e.g., a lithium-ion battery) are generally prepared by mixing an active material, a conductive agent, a thickener, a binder, and a solvent, and applying the mixed slurry to a current collector. Also, the theoretical capacity of an electrochemical device varies depending on the type of active material. As the cycle progresses, an electrochemical device generally experiences a decrease in charge / discharge capacity. This is because, during the charging and / or discharging process of the electrochemical device, changes occur at the electrode interface, causing the electrode active material to lose its function.

[0046] The present invention can guarantee the stability of the electrode sheet of an electrochemical device during cycling, avoid peeling of the negative electrode due to expansion and contraction during cycling, and thereby improve the cycle characteristics of the electrochemical device by using an electrode sheet having a specific adhesive force. The electrode sheet having a specific adhesive force of the present invention can be achieved by controlling the structure of the electrode sheet and the type of functional groups of the binder.

[0047] In some embodiments of the present invention, an electrochemical device including the following negative electrode, positive electrode, and electrolyte is provided.

[0048] [Negative electrode] As shown in FIGS. 1 to 2, the negative electrode sheet in some embodiments of the present invention includes a negative electrode current collector 10 and a film sheet 20. Here, the adhesive force between the film sheet 20 and the negative electrode current collector 10 is ≧20 N / m. The film sheet 20 includes an undercoat layer 201 provided on the surface of the negative electrode current collector 10 and an active material layer 202 provided on the surface of the undercoat layer 201, and the composition of the undercoat layer 201 includes a first binder and a first conductive agent.

[0049] When the negative electrode is provided with an undercoat layer containing a first binder and a first conductive agent on the film piece, the adhesion between the film piece and the negative electrode current collector is improved, thereby significantly improving the cycle and shape stability of the negative electrode. Specifically, on the one hand, the presence of the undercoat layer can improve the surface defects of the negative electrode current collector, strengthen the riveting joint action between the active material layer and the electrode piece, increase the adhesion between the undercoat layer and the negative electrode current collector, thereby improving the adhesion between the entire film piece and the current collector and reducing the risk of peeling off of the film piece. On the other hand, taking the application of the negative electrode to a lithium-ion battery as an example, the presence of the undercoat layer can play a good buffering role. When lithium ions are inserted into the negative electrode active material and expand, the undercoat layer avoids the expanded active material from directly applying a force to the surface of the current collector. If a direct force is applied to the surface of the current collector, the current collector in that direction cannot be fixed and displaced. Therefore, the active material can only expand on the outer surface of the film piece as a whole. When the active material releases lithium ions and contracts, each part of the active material tends to contract synchronously or the inner part with higher electronic conductivity may contract faster, causing the active material in close contact with the surface of the original current collector to separate from the current collector, resulting in the dropout of the film piece, an increase in the internal resistance, and deterioration of the cycle characteristics. Based on this, the electrode piece of the embodiment of the present invention can significantly improve the adhesion between the film piece and the current collector. In some embodiments of the present invention, the adhesion between the film piece and the current collector is limited to ≧20 N / m. By using an electrode piece with a specific adhesion, the stability of the electrode piece during the cycle of the electrochemical device is ensured, peeling due to expansion and contraction during the cycle of the electrode piece is avoided, and the cycle characteristics of the electrochemical device are improved.

[0050] In some embodiments, the adhesion between the film piece and the current collector is ≧80 N / m, and more preferably, in some embodiments, the adhesion between the film piece and the current collector is ≧100 N / m, and even more preferably, in some embodiments, the adhesion between the film piece and the current collector is ≧500 N / m. For example, the adhesion between the film piece and the current collector is 20 N / m, 60 N / m, 80 N / m, 100 N / m, 120 N / m, 130 N / m, 160 N / m, 180 N / m, 220 N / m, 300 N / m, 400 N / m, 500 N / m, 540 N / m, 600 N / m, 630 N / m, etc.

[0051] In some embodiments, the thickness of the undercoat layer is 100 nm (nanometers) to 2 μm (micrometers), and preferably, in some embodiments, the thickness of the undercoat layer is 100 nm to 1000 nm, and even more preferably, in some embodiments, the thickness of the undercoat layer is 100 nm to 800 nm. It is not preferable for the thickness of the undercoat layer to be too large, and it is preferable for the thickness of the undercoat layer to be on the nanoscale, which helps to obtain the desired adhesion between the film piece and the current collector and helps to obtain better film piece resistance and cycle stability. Typically but not limitedly, the thickness of the undercoat layer is, for example, 100 nm, 200 nm, 300 nm, 400 nm, 500 nm, 600 nm, 800 nm, 900 nm, 950 nm, 999 nm, 1 μm, 1.5 μm, 2 μm, as well as ranges formed by any two of these values and any value within the ranges.

[0052] In some embodiments, when the average particle diameter of the particles of the first conductive agent or the average diameter of the tubes is D and the thickness of the undercoat layer is H, D / H is 0.25 to 1.5, preferably 0.5 to 1.25.

[0053] It should be understood that the form of the first conductive agent may be particulate or tubular. When the form of the first conductive agent is particulate, the relationship between the average particle diameter D of the particles of the first conductive agent and the thickness H of the undercoat layer satisfies that D / H is 0.5 to 1.25. When the form of the first conductive agent is tubular, the relationship between the average diameter D of the tubes of the first conductive agent and the thickness H of the undercoat layer satisfies that D / H is 0.5 to 1.25. Typically but not limitedly, the average particle diameter of the particles or the average diameter D of the tubes / the thickness H of the undercoat layer is, for example, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, 1.1, 1.2, 1.25, and any range formed by any two of these values and any value within the range. When the ratio of the average particle diameter of the particles or the average diameter of the tubes to the thickness of the undercoat layer is within the above range, the electrode tab can have better Electrode resistance and cycle stability. In some embodiments of the present invention, when the average particle diameter of the particles or the average diameter D of the tubes / the thickness H of the undercoat layer is less than 0.5, there is an excessive amount of the first conductive agent which is small particles in the undercoat layer, and due to the lamination between the excessive amount of the first conductive agent which is small particles, there is an excessive interfacial resistance, and further Electrode the resistance increases and the cycle stability decreases. When the average particle diameter of the particles or the average diameter D of the tubes / the thickness H of the undercoat layer exceeds 1.25, the distribution of the first conductive agent in the undercoat layer tends to be non-uniform, Electrode the resistance becomes high and the cycle characteristics are affected.

[0054] In some embodiments, Electrode the resistance is 3 mΩ to 50 mΩ. Preferably, in some embodiments, Electrode the resistance is 3 mΩ to 30 mΩ. Typically but not limitedly, Electrode the resistance is, for example, 3 mΩ, 5 mΩ, 6 mΩ, 9 mΩ, 10 mΩ, 15 mΩ, 20 mΩ, 22 mΩ, 26 mΩ, 30 mΩ, 50 mΩ, and any range formed by any two of these values and any value within the range.

[0055] In some embodiments, the compression density of the film piece is 1.30 g / cm 3 ~1.80 g / cm 3 . Typically but not limitedly, the compression density of the film piece is, for example, 1.30 g / cm 3 , 1.40 g / cm 3 , 1.50 g / cm 3 , 1.55 g / cm 3 , 1.60 g / cm 3 , 1.70 g / cm 3 , 1.75 g / cm 3 , 1.80 g / cm 3 , and any range formed by any two of these values and any value within the range. Within the appropriate compression density range of the film piece, it helps to reduce the risk of the electrode tab peeling off, ensures the presence of an undercoat layer between the active material layer and the current collector, the undercoat layer can perform riveting and buffering functions, and further helps to obtain better cycle stability and rate performance.

[0056] In some embodiments, the porosity of the film piece is 20% - 50%. Preferably, in some embodiments, the porosity of the film piece is 25% - 40%. Typically but not limitedly, the porosity of the film piece is, for example, 20%, 22%, 24%, 25%, 26%, 28%, 30%, 32%, 35%, 37%, 40%, 45%, 50%, and any range formed by any two of these values and any value within the range. Within the appropriate porosity range of the film piece, it helps to reduce the risk of the electrode tab peeling off, ensures the presence of an undercoat layer between the active material layer and the current collector, the undercoat layer can perform riveting and buffering functions, can contact the electrolyte sufficiently, and further helps to obtain better cycle stability and rate performance.

[0057] In some embodiments, the mass content of the first binder in the undercoat layer is 20% to 95%. Typically but not limitedly, the mass content of the first binder in the undercoat layer is, for example, 20%, 30%, 40%, 50%, 60%, 65%, 70%, 72%, 80%, 83%, 85%, 90%, 91%, 95%, as well as ranges formed by any two of these values and any value within the ranges. By increasing the content of the first binder in the undercoat layer, the adhesion between the film piece and the current collector can be improved, and a pole piece with higher adhesion can be obtained.

[0058] In some embodiments, the mass content of the first conductive agent in the undercoat layer is 5% to 80%. Typically but not limitedly, the mass content of the first conductive agent in the undercoat layer is, for example, 5%, 10%, 20%, 30%, 40%, 50%, 55%, 60%, 70%, 80%, as well as ranges formed by any two of these values and any value within the ranges.

[0059] In some embodiments, the first binder may include at least one of a carbon-carbon double bond, a carboxyl group, a carbonyl group, a carbon-nitrogen single bond, a hydroxyl group, an ester group, an acyl group, and an aryl group. Preferably, in some embodiments, the first binder may include at least one of a carboxyl group, a carbonyl group, a carbon-nitrogen single bond, a hydroxyl group, an ester group, and an acyl group. By adopting a first binder containing one or more of the functional groups of a carboxyl group, a carbonyl group, a carbon-nitrogen single bond, a hydroxyl group, an ester group, and an acyl group, the adhesion between the film piece and the current collector can be significantly improved. This is because the polarity of the above functional groups is strong and there is a strong attracting effect with the metal current collector rich in electrons, thereby making the shape stability of the film piece more stable, and it can also maintain excellent shape stability for high-expansion silicon-based active materials.

[0060] In some embodiments, the first binder may include at least one of SBR (styrene-butadiene rubber), PAA (polyacrylic acid), PVP (polyvinylpyrrolidone), and PAM (polyacrylamide).

[0061] In some embodiments, the first conductive agent includes, but is not limited to, at least one of conductive carbon black, ketjen black, single-walled carbon nanotubes, and multi-walled carbon nanotubes.

[0062] In some embodiments, the composition of the active material layer includes an active material and a second binder.

[0063] In some embodiments, the active material may include at least one of a graphite-based material and a silicon-based material.

[0064] In some embodiments, the silicon-based material may include at least one of silicon, silicon oxide, silicon-carbon composite, and silicon alloy. Preferably, in some embodiments, the silicon-based material is pure silicon, SiO x (0 < x ≦ 2) and at least one of a silicon-carbon composite, where preferably the silicon-based material is SiO x (1 < x ≦ 2). The negative electrode active material may be used alone or in combination.

[0065] In some embodiments, the active material layer further includes a second conductive agent. In the film piece, the undercoat layer may or may not include the first conductive agent, and the active material layer may or may not include the second conductive agent.

[0066] According to some embodiments of the present invention, the first binder in the undercoat layer and the second binder in the active material layer may be of the same type or different types. The first conductive agent in the undercoat layer and the second conductive agent in the active material layer may be of the same type or different types.

[0067] The second binder in the active material layer can improve the adhesion between the negative electrode active material particles and the adhesion between the negative electrode active material and the undercoat layer. The embodiments of the present invention and the types of the binder in the negative electrode active material layer are not particularly limited, as long as they are stable with respect to the electrolytic solution and the solvent used during electrode fabrication. Exemplarily, in some embodiments, the second binder includes a resin binder. Examples of the resin binder include, but are not limited to, fluororesin, polyacrylonitrile (PAN), polyimide resin, acrylic resin, polyolefin resin, etc. When preparing the negative electrode active material layer slurry using an aqueous solvent, the second binder includes, but is not limited to, carboxymethyl cellulose (CMC) or its salt, styrene-butadiene rubber (SBR), polyacrylic acid (PAA) or its salt, polyvinyl alcohol, etc. Preferably, in some embodiments, the second binder may include at least one of PAA (polyacrylic acid), PVP (polyvinylpyrrolidone), PAM (polyacrylamide), SBR (styrene-butadiene rubber), and CMC (carboxymethyl cellulose).

[0068] In some embodiments, the molecular weight of the first binder is less than 1,500,000. The molecular weight of the second binder is less than 1,500,000.

[0069] In some embodiments, the second conductive agent includes, but is not limited to, at least one of conductive carbon black, ketjen black, single-walled carbon nanotubes, and multi-walled carbon nanotubes.

[0070] In some embodiments, the active material layer contains, by mass content, 80% to 99% active material, 0.8% to 20% second binder, and 0 to 5% second conductive agent. Typically but not limitedly, in the active material layer, the mass content of the active material is, for example, 80%, 82%, 84%, 85%, 86%, 88%, 90%, 92%, 94%, 95%, 96%, 99%, as well as the ranges formed by any two of these values and any value within the ranges. The mass content of the second binder is, for example, 0.8%, 1%, 2%, 4%, 5%, 6%, 8%, 10%, 12%, 15%, 18%, 20%, as well as the ranges formed by any two of these values and any value within the ranges. The mass content of the second conductive agent is, for example, 0, 1%, 2%, 3%, 4%, 5%, as well as the ranges formed by any two of these values and any value within the ranges.

[0071] In some embodiments, in order to prevent the unintended precipitation of lithium metal on the negative electrode during charging, the chargeable capacity of the negative electrode active material is greater than the discharge capacity of the positive electrode active material.

[0072] As the negative electrode current collector for holding the negative electrode active material, any known current collector can be arbitrarily used. Examples of the negative electrode current collector include, but are not limited to, metal materials such as aluminum, copper, nickel, stainless steel, nickel-plated steel, etc. In some embodiments, the negative electrode current collector is copper.

[0073] When the negative electrode current collector is a metal material, the form of the negative electrode current collector includes, but is not limited to, metal foil, metal cylinder, metal coil, metal plate, metal thin film, metalplate net, punching metal, foamed metal, etc. In some embodiments, the negative electrode current collector is a metal thin film. In some embodiments, the negative electrode current collector is copper foil. In some embodiments, the negative electrode current collector is rolled copper foil by rolling method or electrolytic copper foil by electrolysis method.

[0074] In some embodiments, the thickness of the negative electrode current collector exceeds 1 μm, or exceeds 5 μm. In some embodiments, the thickness of the negative electrode current collector is less than 100 μm, or less than 50 μm. In some embodiments, the thickness of the negative electrode current collector is within the range constituted by any two of the above-mentioned values.

[0075] First, on the negative electrode current collector, an undercoat layer slurry containing a first binder and a first conductive agent is applied, and after drying, a positive electrode active material and a second binder are further applied to the undercoat layer. A positive electrode active material layer slurry is applied, dried, and then rolled to form a negative electrode film piece on the negative electrode current collector to obtain a negative electrode (negative electrode sheet).

[0076] [Positive electrode] The positive electrode sheet in some embodiments of the present invention includes a positive electrode current collector and a positive electrode active material layer provided on one or two surfaces of the positive electrode current collector.

[0077] Here, the positive electrode active material layer contains a positive electrode active material. The positive electrode active material layer may be a single layer or a multi-layer. Each layer in the multi-layer positive electrode active material layer may contain the same or different positive electrode active materials. Taking the case where the electrochemical device is a lithium-ion battery as an example, the positive electrode active material is a material capable of reversibly inserting and desorbing metal ions such as any lithium ions. In some embodiments, in order to prevent the unintended precipitation of lithium metal on the negative electrode during charging, the discharge capacity of the positive electrode active material is smaller than the chargeable capacity of the negative electrode active material.

[0078] According to some embodiments of the present invention, the type of the positive electrode active material is not particularly limited, and any material capable of occluding and releasing metal ions (for example, lithium ions) in an electrochemical manner may be used. Exemplarily, in some embodiments, the positive electrode active material is a material containing lithium and at least one transition metal. Examples of the positive electrode active material include, but are not limited to, lithium transition metal composite oxides and lithium-containing transition metal phosphate compounds.

[0079] In some embodiments, the transition metals in the lithium transition metal composite oxide include V, Ti, Cr, Mn, Fe, Co, Ni, Cu, etc. In some embodiments, the lithium transition metal composite oxide is a lithium-cobalt composite oxide such as LiCoO2; a lithium-nickel composite oxide such as LiNiO2; a lithium-manganese composite oxide such as LiMnO2, LiMn2O4, Li2MnO4; LiNi 1 / 3 Mn 1 / 3 Co 1 / 3 O2, LiNi 0.5 Mn 0.3 Co 0.2 O2 and other lithium-nickel-manganese-cobalt composite oxides, where a part of the transition metal atoms that are the main components of these lithium transition metal composite oxides are substituted with other elements such as Na, K, B, F, Al, Ti, V, Cr, Mn, Fe, Co, Li, Ni, Cu, Zn, Mg, Ga, Zr, Si, Nb, Mo, Sn, W. Examples of the lithium transition metal composite oxide are LiNi 0.5 Mn 0.5 O2, LiNi 0.85 Co 0.10 Al 0.05 O2, LiNi 0.33 Co 0.33 Mn 0.33 O2, LiNi 0.45 Co 0.10 Al 0.45 O2, LiMn 1.8 Al 0.2 O4 and LiMn 1.5 Ni 0.5 O4, etc., but are not limited thereto. Examples of the combination of the lithium transition metal composite oxides include, but are not limited to, the combination of LiCoO2 and LiMn2O4. Here, a part of Mn in LiMn2O4 may be substituted with a transition metal (for example, LiNi 0.33 Co 0.33 Mn 0.33 O2), and a part of Co in LiCoO2 may be substituted with a transition metal.

[0080] In some embodiments, the transition metals in the lithium-containing transition metal phosphate compound include V, Ti, Cr, Mn, Fe, Co, Ni, Cu, etc. In some embodiments, the lithium-containing transition metal phosphate compounds include iron phosphates such as LiFePO4, Li3Fe2(PO4)3, LiFeP2O7; cobalt phosphates such as LiCoPO4, where a part of the transition metal atoms that are the main components of these lithium-containing transition metal phosphate compounds are substituted with other elements such as Al, Ti, V, Cr, Mn, Fe, Co, Li, Ni, Cu, Zn, Mg, Ga, Zr, Nb, Si, etc.

[0081] In some embodiments, the powder material of the lithium transition metal oxide Li a M b O2 is used, where 0.9 < a < 1.1, 0.9 < b < 1.1, and M is a transition metal mainly selected from Mn, Co, or Ni, where the composition of M varies with the particle size.

[0082] In some embodiments, in the powdery electrode active material of the lithium transition metal oxide Li a M b O2, M = A Z A’ Z’ M’ 1-Z-Z’ , M’ = Mn x Ni y Co 1-x-y , 0 ≤ y ≤ 1, 0 ≤ x ≤ 1, 0 ≤ Z + Z’ < 0.1, Z’ < 0.02, A is at least one selected from the elements Al, Mg, Ti, Cr, and A’ is at least one selected from the elements F, Cl, S, Zr, Ba, Y, Ca, B, Be, Sn, Sb, Na, Zn.

[0083] In some embodiments, the average composition of the transition metal is M = Mn x Ni y Co 1-x-y , where 0.03 < x < 0.35.

[0084] In some embodiments, the average composition of the transition metal is M = Mn x Niy Co 1-x-y where 0.03 < x and x + y < 0.7.

[0085] In some embodiments, in the powdery electrode active material of Li a M b O2, substantially all portions of all particles have a layered crystal structure. Larger particles have the composition Li a M b O2, where M = Mn x Ni y Co 1-x-y , and x + y < 0.35. For smaller particles, the composition is Li a M b O2, where M = Mn x’ Ni y’ Co 1-x’-y’ , having at least 10% less Co, (1 - x' - y') < 0.9×(1 - x - y), and at least 5% more Mn compared to larger particles, and x' - x > 0.05. Thereby, a powder with a correlation between size and composition can be obtained. That is, one component has large particles (for example, concentrated in the distribution of ≧20 μm), and this component can diffuse rapidly in the bulk. The other component has small particles (for example, distributed around 5 μm), and this component can ensure safety. Therefore, an electrode active material is provided that combines high cycle stability and high safety with high volume energy density and high weight energy density.

[0086] In some embodiments, the positive electrode active material has a wide particle size distribution defined by a particle size ratio of large particles to small particles greater than 3, Dv90 / Dv10 > 3. Here, Dv90 represents the particle size at which the volume cumulative reaches 90% from the small particle size side in the volume-based particle size distribution. Dv10 represents the particle size at which the volume cumulative reaches 10% from the small particle size side in the volume-based particle size distribution. The particle size distribution of the powder can be determined by an appropriate method known in the art. Appropriate methods include, for example, the method by laser diffraction or sieving using a set of sieves with different mesh sizes.

[0087] In some embodiments, the single particle is essentially a lithium transition metal oxide, the single particle has Co, and the content of the single particle in the transition metal increases continuously with the particle size.

[0088] In some embodiments, the single particle also contains Mn in the transition metal, and the Mn content decreases continuously with the particle size.

[0089] In some embodiments, the large particles have large particles close to the LiCoO2 composition that can obtain a high Li diffusion coefficient, and thus sufficient rate performance can be obtained. The large particles occupy only a very small part of the total surface area of the positive electrode. For this reason, the heat released by reacting with the electrolyte at the surface or the outer part is limited. As a result, the number of large particles decreases and the safety decreases. The small particles have a composition containing less Co in order to enhance safety. The lower lithium diffusion coefficient can be tolerated in small particles without significant loss of rate performance due to the short length of the solid diffusion path.

[0090] In some embodiments, the preferred composition of the small particles contains stabilizing elements such as less Co and more Mn. Slower Li bulk diffusion can be tolerated, but the surface stability is high. In the cathode active material powder of the present invention, the preferred composition of the large particles contains more Co and less Mn, because while rapid bulk diffusion of lithium is required, slightly lower surface stabilization can be tolerated.

[0091] In some embodiments, the composition is Li x Inside a single particle that is MO2, it is preferable that at least 80% by weight of M is cobalt or nickel. In some embodiments, the inner part of the particle has a composition close to LiCoO2. The outer part is lithium manganese nickel cobalt oxide.

[0092] A powdery electrode active material whose size and composition are correlated can be prepared by the following method. At least one transition metal-containing precipitate is deposited on seed particles having a transition metal composition different from that of the precipitate, a controlled amount of a lithium precursor is added, and at least one heat treatment is performed, where substantially all of the obtained particles contain an internal core derived from the seed completely covered by a layer derived from the precipitate.

[0093] [Electrolyte] The electrolyte used in the electrochemical device of the present invention includes an electrolyte and a solvent that dissolves the electrolyte. In some embodiments, the electrolyte used in the electrochemical device of the present invention further includes an additive.

[0094] In some embodiments, the electrolyte further includes any non-aqueous solvent used as a solvent for electrolytes known in the prior art.

[0095] In some embodiments, the non-aqueous solvent includes, but is not limited to, one or more of cyclic carbonates, chain carbonates, cyclic carboxylic acid esters, chain carboxylic acid esters, cyclic ethers, chain ethers, phosphorus-containing organic solvents, sulfur-containing organic solvents, and aromatic fluorine-containing solvents.

[0096] In some embodiments, examples of the cyclic carbonate include, but are not limited to, one or more of ethylene carbonate (EC), propylene carbonate (PC), and butylene carbonate. In some embodiments, the cyclic carbonate has 3 to 6 carbon atoms.

[0097] In some embodiments, examples of the chain carbonate include, but are not limited to, one or more of chain carbonates such as dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate (DEC), methyl-n-propyl carbonate, ethyl-n-propyl carbonate, di-n-propyl carbonate, etc. Examples of the chain carbonate substituted with fluorine include, but are not limited to, one or more of bis(fluoromethyl) carbonate, bis(difluoromethyl) carbonate, bis(trifluoromethyl) carbonate, bis(2-fluoroethyl) carbonate, bis(2,2-difluoroethyl) carbonate, bis(2,2,2-trifluoroethyl) carbonate, 2-fluoroethyl methyl carbonate, 2,2-difluoroethyl methyl carbonate, and 2,2,2-trifluoroethyl methyl carbonate, etc.

[0098] In some embodiments, examples of the cyclic carboxylic acid ester include, but are not limited to, one or more of γ-butyrolactone and γ-valerolactone, etc. In some embodiments, a part of the hydrogen atoms of the cyclic carboxylic acid ester may be substituted with fluorine.

[0099] In some embodiments, examples of the chain carboxylic acid esters include, but are not limited to, one or more of methyl acetate, ethyl acetate, propyl acetate, isopropyl acetate, butyl acetate, sec-butyl acetate, isobutyl acetate, t-butyl acetate, methyl propionate, ethyl propionate, propyl propionate, isopropyl propionate, methyl butyrate, ethyl butyrate, propyl butyrate, methyl isobutyrate, ethyl isobutyrate, methyl valerate, ethyl valerate, methyl pivalate, and ethyl pivalate. In some embodiments, some of the hydrogen atoms of the chain carboxylic acid esters may be substituted with fluorine. In some embodiments, examples of the chain carboxylic acid esters substituted with fluorine include, but are not limited to, methyl trifluoroacetate, ethyl trifluoroacetate, propyl trifluoroacetate, butyl trifluoroacetate, and 2,2,2-trifluoroethyl trifluoroacetate.

[0100] In some embodiments, examples of the cyclic ethers include, but are not limited to, one or more of tetrahydrofuran, 2-methyltetrahydrofuran, 1,3-dioxolane, 2-methyl-1,3-dioxolane, 4-methyl-1,3-dioxolane, 1,3-dioxane, 1,4-dioxane, and dimethoxypropane.

[0101] In some embodiments, examples of the chain ethers include, but are not limited to, one or more of dimethoxymethane, 1,1-dimethoxyethane, 1,2-dimethoxyethane, diethoxymethane, 1,1-diethoxyethane, 1,2-diethoxyethane, ethoxymethoxymethane, 1,1-ethoxymethoxyethane, and 1,2-ethoxymethoxyethane.

[0102] In some embodiments, examples of the phosphorus-containing organic solvents include, but are not limited to, one or more of trimethyl phosphate, triethyl phosphate, dimethylethyl phosphate, methyldiethyl phosphate, ethylene methyl phosphate, ethylene ethyl phosphate, triphenyl phosphate, trimethyl phosphite, triethyl phosphite, triphenyl phosphite, tris(2,2,2-trifluoroethyl) phosphate, and tris(2,2,3,3,3-pentafluoropropyl) phosphate.

[0103] In some embodiments, examples of the sulfur-containing organic solvents include, but are not limited to, one or more of sulfolane, 2-methyl sulfolane, 3-methyl sulfolane, dimethyl sulfone, diethyl sulfone, ethyl methyl sulfone, methyl propyl sulfone, dimethyl sulfoxide, methyl methanesulfonate, ethyl methanesulfonate, methyl ethanesulfonate, ethyl ethanesulfonate, dimethyl sulfate, diethyl sulfate, and dibutyl sulfate. In some embodiments, some of the hydrogen atoms of the sulfur-containing organic solvent may be substituted with fluorine.

[0104] In some embodiments, the aromatic fluorine-containing solvents include, but are not limited to, one or more of fluorobenzene, difluorobenzene, trifluorobenzene, tetrafluorobenzene, pentafluorobenzene, hexafluorobenzene, and trifluoromethylbenzene.

[0105] In some embodiments, the solvent used in the electrolyte of the present invention includes cyclic carbonates, chain carbonates, cyclic carboxylic acid esters, chain carboxylic acid esters, or combinations thereof. In some embodiments, the solvent used in the electrolyte of the present invention includes at least one of ethylene carbonate, propylene carbonate, diethyl carbonate, ethyl propionate, propyl propionate, n-propyl acetate or ethyl acetate. In some embodiments, the solvent used in the electrolyte of the present invention includes ethylene carbonate, propylene carbonate, diethyl carbonate, ethyl propionate, propyl propionate, γ-butyrolactone, or combinations thereof.

[0106] After adding a chain carboxylic acid ester and / or a cyclic carboxylic acid ester to the electrolyte, the chain carboxylic acid ester and / or the cyclic carboxylic acid ester can form a passivation film on the electrode surface, thereby improving the capacity retention rate after the electrochemical device undergoes intermittent charge cycles. In some embodiments, the electrolyte includes 1% to 60% of a chain carboxylic acid ester, a cyclic carboxylic acid ester, or a combination thereof. In some embodiments, the electrolyte includes ethyl propionate, propyl propionate, γ-butyrolactone, or combinations thereof, and the content of this combination relative to the total weight of the electrolyte is 1% to 60%, 10% to 60%, 10% to 50%, 20% to 50%. In some embodiments, the electrolyte contains 1% to 60%, 10% to 60%, 20% to 50%, 20% to 40% or 30% of propyl propionate relative to the total weight of the electrolyte.

[0107] In some embodiments, the electrolyte includes additives. Examples of the additives include, but are not limited to, one or more of fluorocarbonates, ethylene carbonate containing a carbon-carbon double bond, a compound containing a sulfur-oxygen double bond (containing an S=O double bond), and acid anhydrides. Preferably, the additive includes a compound containing an S=O double bond.

[0108] In some embodiments, the content of the additive in the total weight of the electrolyte is 0.01% to 15%, 0.1% to 10% or 1% to 5%.

[0109] According to the embodiments of the present invention, with respect to the total weight of the electrolyte, the content of propionate is 1.5 to 30 times, 1.5 to 20 times, 2 to 20 times or 5 to 20 times that of the additive.

[0110] In some embodiments, the additive includes one or more kinds of fluorocarbonates. During charging / discharging of the lithium-ion battery, the fluorocarbonate can cooperate with propionate to form a stable protective film on the surface of the negative electrode, thereby suppressing the decomposition reaction of the electrolyte.

[0111] In some embodiments, the fluorocarbonate has the formula C=O(OR1)(OR2), where R1 and R2 are each independently selected from an alkyl group or a halogenated alkyl group having 1 to 6 carbon atoms, and at least one of R1 and R2 is selected from a fluoroalkyl group having 1 to 6 carbon atoms, and R1 and R2 optionally form a 5- to 7-membered ring together with the atoms to which they are attached.

[0112] In some embodiments, examples of the fluorocarbonate include, but are not limited to, one or more of fluoroethylene carbonate, cis-4,4-difluoroethylene carbonate, trans-4,4-difluoroethylene carbonate, 4,5-difluoroethylene carbonate, 4-fluoro-4-methylethylene carbonate, 4-fluoro-5-methylethylene carbonate, methyl trifluoromethyl carbonate, methyl trifluoroethyl carbonate, and ethyl trifluoroethyl carbonate, etc.

[0113] In some embodiments, the additive includes one or more ethylene carbonates containing a carbon-carbon double bond. Examples of ethylene carbonates containing a carbon-carbon double bond include, but are not limited to, one or more of vinylene carbonate, methyl vinylene carbonate, ethyl vinylene carbonate, 1,2-dimethyl vinylene carbonate, 1,2-diethyl vinylene carbonate, fluorovinylene carbonate, trifluoromethyl vinylene carbonate, vinyl ethylene carbonate, 1-methyl-2-vinyl ethylene carbonate, 1-ethyl-2-vinyl ethylene carbonate, 1-n-propyl-2-vinyl ethylene carbonate, 1-methyl-2-vinyl ethylene carbonate, 1,1-divinyl ethylene carbonate, 1,2-divinyl ethylene carbonate, 1,1-dimethyl-2-methylene ethylene carbonate, and 1,1-diethyl-2-methylene ethylene carbonate. In some embodiments, the ethylene carbonate containing a carbon-carbon double bond includes vinylene carbonate in view of easy availability and the ability to achieve further excellent effects.

[0114] In some embodiments, the additive includes one or more compounds containing a sulfur-oxygen double bond. Examples of compounds containing a sulfur-oxygen double bond include, but are not limited to, one or more of cyclic sulfates, chain sulfates, chain sulfonates, cyclic sulfonates, chain sulfites, and cyclic sulfites.

[0115] Here, examples of cyclic sulfates include, but are not limited to, one or more of 1,2-ethylene sulfate, 1,2-propylene sulfate, 1,3-propylene sulfate, 1,2-butylene sulfate, 1,3-butylene sulfate, 1,4-butylene sulfate, 1,2-pentylene sulfate, 1,3-pentylene sulfate, 1,4-pentylene sulfate, and 1,5-pentylene sulfate.

[0116] Examples of chain sulfates include, but are not limited to, one or more of dimethyl sulfate, ethyl methyl sulfate, and diethyl sulfate.

[0117] Examples of chain sulfonic acid esters include, but are not limited to, one or more of fluorosulfonic acid esters such as methyl fluorosulfonate and ethyl fluorosulfonate, methyl methanesulfonate, ethyl methanesulfonate, butyl methanesulfonate, methyl 2-(methanesulfonyloxy)propionate, and ethyl 2-(methanesulfonyloxy)propionate.

[0118] Examples of cyclic sulfonic acid esters include, but are not limited to, one or more of 1,3-propanesultone, 1-fluoro-1,3-propanesultone, 2-fluoro-1,3-propanesultone, 3-fluoro-1,3-propanesultone, 1-methyl-1,3-propanesultone, 2-methyl-1,3-propanesultone, 3-methyl-1,3-propanesultone, 1-propene-1,3-sultone, 2-propene-1,3-sultone, 1-fluoro-1-propene-1,3-sultone, 2-fluoro-1-propene-1,3-sultone, 3-fluoro-1-propene-1,3-sultone, 1-fluoro-2-propene-1,3-sultone, 2-fluoro-2-propene-1,3-sultone, 3-fluoro-2-propene-1,3-sultone, 1-methyl-1-propene-1,3-sultone, 2-methyl-1-propene-1,3-sultone, 3-methyl-1-propene-1,3-sultone, 1-methyl-2-propene-1,3-sultone, 2-methyl-2-propene-1,3-sultone, 3-methyl-2-propene-1,3-sultone, 1,4-butanesultone, 1,5-pentanesultone, methylene methanedisulfonate, and ethylene methanedisulfonate.

[0119] Examples of chain sulfites include, but are not limited to, one or more of dimethyl sulfite, ethyl methyl sulfite, and diethyl sulfite.

[0120] Examples of the cyclic sulfite include, but are not limited to, one or more of 1,2-ethylene sulfite, 1,2-propylene sulfite, 1,3-propylene sulfite, 1,2-butylene sulfite, 1,3-butylene sulfite, 1,4-butylene sulfite, 1,2-pentylene sulfite, 1,3-pentylene sulfite, 1,4-pentylene sulfite, and 1,5-pentylene sulfite.

[0121] In some embodiments, the additive includes one or more of acid anhydrides. Examples of the acid anhydride include, but are not limited to, one or more of cyclic phosphoric anhydrides, carboxylic anhydrides, disulfonic anhydrides, and carboxylic sulfonic anhydrides. Examples of the cyclic phosphoric anhydride include, but are not limited to, one or more of trimethyl phosphonic anhydride, triethyl phosphonic anhydride, and tripropyl phosphonic anhydride. Examples of the carboxylic anhydride include, but are not limited to, one or more of succinic anhydride, glutaric anhydride, and maleic anhydride. Examples of the disulfonic anhydride include, but are not limited to, one or more of ethanedisulfonic anhydride and propanedisulfonic anhydride. Examples of the carboxylic sulfonic anhydride include, but are not limited to, one or more of sulfobenzoic anhydride, sulfopropionic anhydride, and sulfobutanoic anhydride.

[0122] In some embodiments, the additive is a combination of a fluorocarbonate and ethylene carbonate containing a carbon-carbon double bond. In some embodiments, the additive is a combination of a fluorocarbonate and a compound containing a sulfur-oxygen double bond. In some embodiments, the additive is a combination of a fluorocarbonate and a compound having 2 to 4 cyano groups. In some embodiments, the additive is a combination of a fluorocarbonate and a cyclic carboxylic acid ester. In some embodiments, the additive is a combination of a fluorocarbonate and a cyclic phosphoric anhydride. In some embodiments, the additive is a combination of a fluorocarbonate and a carboxylic anhydride. In some embodiments, the additive is a combination of a fluorocarbonate and a sulfonic anhydride. In some embodiments, the additive is a combination of a fluorocarbonate and a carboxylic sulfonic anhydride.

[0123] According to some embodiments of the present invention, the electrolyte is not particularly limited, and a substance known as an electrolyte may be arbitrarily used. In the case of a lithium secondary battery, a lithium salt is usually used.Examples of electrolytes include, but are not limited to, inorganic lithium salts such as LiPF6, LiBF4, LiClO4, LiAlF4, LiSbF6, LiTaF6, LiWF7; lithium tungstates such as LiWOF5; lithium carboxylate salts such as HCO2Li, CH3CO2Li, CH2FCO2Li, CHF2CO2Li, CF3CO2Li, CF3CH2CO2Li, CF3CF2CO2Li, CF3CF2CF2CO2Li, CF3CF2CF2CF2CO2Li; lithium sulfonate salts such as FSO3Li, CH3SO3Li, CH2FSO3Li, CHF2SO3Li, CF3SO3Li, CF3CF2SO3Li, CF3CF2CF2SO3Li, CF3CF2CF2CF2SO3Li; lithium imide salts such as LiN(FCO)2, LiN(FCO)(FSO2), LiN(FSO2)2, LiN(FSO2)(CF3SO2), LiN(CF3SO2)2, LiN(C2F5SO2)2, lithium cyclic 1,2-perfluoroethanedisulfonylimide, lithium cyclic 1,3-perfluoropropanedisulfonylimide, LiN(CF3SO2)(C4F9SO2); lithium methide salts such as LiC(FSO2)3, LiC(CF3SO2)3, LiC(C2F5SO2)3; lithium (malonato)borate salts such as lithium bis(malonato)borate, lithium difluoro(malonato)borate; lithium (malonato)phosphate salts such as lithium tris(malonato)phosphate, lithium difluorobis(malonato)phosphate, lithium tetrafluoro(malonato)phosphate; and fluorine-containing organic lithium salts such as LiPF4(CF3)2, LiPF4(C2F5)2, LiPF4(CF3SO2)2, LiPF4(C2F5SO2)2, LiBF3CF3, LiBF3C2F5, LiBF3C3F7, LiBF2(CF3)2, LiBF2(C2F5)2, LiBF2(CF3SO2)2, LiBF2(C2F5SO2)2; lithium oxalatoborate salts such as lithium difluoro(oxalato)borate, lithium bis(oxalato)borate; lithium (oxalato)phosphate salts such as lithium tetrafluoro(oxalato)phosphate, lithium difluorobis(oxalato)phosphate, lithium tris(oxalato)phosphate, etc.

[0124] In some embodiments, the electrolyte is selected from LiPF6, LiSbF6, FSO3Li, CF3SO3Li, LiN(FSO2)2, LiN(FSO2)(CF3SO2), LiN(CF3SO2)2, LiN(C2F5SO2)2, lithium cyclic 1,2-perfluoroethanedisulfonylimide, lithium cyclic 1,3-perfluoropropanedisulfonylimide, LiC(FSO2)3, LiC(CF3SO2)3, LiC(C2F5SO2)3, LiBF3CF3, LiBF3C2F5, LiPF3(CF3)3, LiPF3(C2F5)3, lithium difluoro(oxalato)borate, lithium bis(oxalato)borate or lithium difluorobis(oxalato)phosphate. They contribute to improving the output characteristics, charge and discharge characteristics at high rates, high temperature storage characteristics, cycle characteristics, etc. of the electrochemical device.

[0125] The content of the electrolyte is not particularly limited as long as the effects of the present invention are not impaired. Exemplarily, in some embodiments, the total molar concentration of lithium in the electrolyte solution is 0.3 mol / L or more, more than 0.4 mol / L, or more than 0.5 mol / L. In some embodiments, the total molar concentration of lithium in the electrolyte solution is less than 3 mol / L, less than 2.5 mol / L, or 2.0 mol / L or less. In some embodiments, the total molar concentration of lithium in the electrolyte solution is within the range composed of any two of the above-mentioned values. When the concentration of the electrolyte is within the above-mentioned range, lithium, which is a charged particle, becomes sufficient, and the viscosity can be made within an appropriate range, so it is easy to ensure good electrical conductivity.

[0126] When two or more electrolytes are used in combination, the electrolyte contains at least one salt selected from the group consisting of monofluorophosphate, borate, oxalate, and fluorosulfonate. In some embodiments, the electrolyte contains a salt selected from the group consisting of monofluorophosphate, oxalate, and fluorosulfonate. In some embodiments, the electrolyte contains a lithium salt. In some embodiments, based on the total weight of the electrolyte, the content of the salt selected from the group consisting of monofluorophosphate, borate, oxalate, and fluorosulfonate is more than 0.01% or more than 0.1%. In some embodiments, based on the total weight of the electrolyte, the content of the salt selected from the group consisting of monofluorophosphate, borate, oxalate, and fluorosulfonate is less than 20% or less than 10%. In some embodiments, the content of the salt selected from the group consisting of monofluorophosphate, borate, oxalate, and fluorosulfonate is within the range composed of any two of the above values.

[0127] In some embodiments, the electrolyte contains one or more substances selected from the group consisting of monofluorophosphate, borate, oxalate, and fluorosulfonate, and one or more other salts. Examples of the other salts include the lithium salts exemplified above. In some embodiments, LiPF6, LiN(FSO2)(CF3SO2), LiN(CF3SO2)2, LiN(C2F5SO2)2, lithium cyclic 1,2-perfluoroethanedisulfonylimide, lithium cyclic 1,3-perfluoropropanedisulfonylimide, LiC(FSO2)3, LiC(CF3SO2)3, LiC(C2F5SO2)3, LiBF3CF3, LiBF3C2F5, LiPF3(CF3)3, LiPF3(C2F5)3 are included. In some embodiments, the other salt is LiPF6.

[0128] In some embodiments, the content of other salts is more than 0.01% or more than 0.1% based on the total weight of the electrolyte. In some embodiments, the content of other salts is less than 20%, less than 15%, or less than 10% based on the total weight of the electrolyte. In some embodiments, the content of other salts is within the range composed of any two of the above-mentioned values. The other salts with the above content contribute to the balance between the electrical conductivity and viscosity of the electrolyte solution.

[0129] In addition to the above-mentioned solvent, additives and electrolyte salts, the electrolyte solution may further contain other additives such as a negative electrode film-forming agent, a positive electrode protective agent, an overcharge prevention agent, etc. as required. As the additives, usually, additives used in non-aqueous electrolyte secondary batteries can be used, and examples thereof include, but are not limited to, vinylene carbonate, succinic anhydride, biphenyl, cyclohexylbenzene, 2,4-difluoroanisole, propane sultone, propene sultone, etc. These additives may be used alone or in any combination. The content of these additives in the electrolyte solution is not particularly limited and may be appropriately set according to the type of this additive. In some embodiments, the content of the additive based on the total weight of the electrolyte is less than 5%, within the range of 0.01% to 5%, or within the range of 0.2% to 5%.

[0130] [Separator] A separator is usually provided between the positive electrode and the negative electrode to prevent short circuit. In this case, the electrolyte solution of the present invention is usually impregnated into this separator and used.

[0131] The material and shape of the separator are not particularly limited as long as the effects of the present invention are not significantly impaired. The separator may be a resin, glass fiber, inorganic substance, etc. made of a material stable to the electrolytic solution of the present invention. In some embodiments, the separator includes a porous sheet or a non-woven fabric-like substance with excellent liquid retention properties. Examples of the material of the resin or glass fiber separator include, but are not limited to, polyolefin, aromatic polyamide, polytetrafluoroethylene, polyethersulfone, glass filter, etc. In some embodiments, the material of the separator is a glass filter. In some embodiments, the polyolefin is polyethylene or polypropylene. In some embodiments, the polyolefin is polypropylene. The above-described separator materials may be used alone or in any combination.

[0132] The separator may be a material formed by laminating the above-described materials, and examples thereof include, but are not limited to, a three-layer separator laminated in the order of polypropylene, polyethylene, and polypropylene.

[0133] Examples of the inorganic material include oxides such as aluminum oxide and silicon dioxide; nitrides such as aluminum nitride and silicon nitride; sulfates (e.g., barium sulfate, calcium sulfate, etc.), but are not limited thereto. The form of the inorganic substance includes, but is not limited to, particulate or fibrous forms.

[0134] The separator is in the form of a thin film, and examples thereof include, but are not limited to, non-woven fabrics, woven fabrics, microporous films, etc. In the form of a film, the pore diameter of the separator is 0.01 μm to 1 μm, and the thickness is 5 μm to 50 μm. In addition to the above-mentioned independent film-shaped separator, the following separators can also be used. That is, a separator formed by using a resin binder to form a composite porous layer containing the above-mentioned inorganic particles on the surface of the positive electrode and / or the negative electrode can be used. For example, a separator formed by using a fluororesin as a binder to form a porous layer on both sides of the positive electrode with aluminum oxide particles having a particle size of less than 1 μm for 90% can be used.

[0135] The thickness of the separator is arbitrary. In some embodiments, the thickness of the separator is greater than 1 μm, greater than 5 μm, or greater than 8 μm. In some embodiments, the thickness of the separator is less than 50 μm, less than 40 μm, or less than 30 μm. In some embodiments, the thickness of the separator is within the range composed of any two of the above values. When the thickness of the separator is within the above range, the rate characteristics and energy density of the electrochemical device can be ensured while ensuring insulation and mechanical strength.

[0136] When a porous material such as a porous sheet or non-woven fabric is used as the separator, the porosity of the separator is arbitrary. In some embodiments, the porosity of the separator is greater than 20%, greater than 35%, or greater than 45%. In some embodiments, the porosity of the separator is less than 90%, less than 85%, or less than 75%. In some embodiments, the porosity of the separator is within the range composed of any two of the above values. When the porosity of the separator is within the above range, the resistance of the membrane can be suppressed while ensuring insulation and mechanical strength, and the electrochemical device can be made to have good rate characteristics.

[0137] The average pore diameter of the separator is also arbitrary. In some embodiments, the average pore diameter of the separator is less than 0.5 μm, or less than 0.2 μm. In some embodiments, the average pore diameter of the separator exceeds 0.05 μm. In some embodiments, the average pore diameter of the separator is within the range composed of any two of the above-mentioned values. If the average pore diameter of the separator is outside the above-mentioned range, a short circuit is likely to occur. If the average pore diameter of the separator is within the above range, it is possible to suppress the resistance of the membrane while preventing a short circuit, and the electrochemical device can have good rate characteristics.

[0138] [Electrochemical device assembly] The electrochemical device assembly includes an electrode group, a current collecting structure, an exterior case, and a protection element.

[0139] Electrode group The electrode group may have either a laminated structure formed by laminating the positive electrode and the negative electrode via the separator, or a structure formed by winding the positive electrode and the negative electrode in a spiral shape via the separator. In some embodiments, the ratio of the mass of the electrode group to the internal volume of the battery (electrode group occupancy rate) exceeds 40%, or exceeds 50%. In some embodiments, the electrode group occupancy rate is less than 90%, or less than 80%. In some embodiments, the electrode group occupancy rate is within the range composed of any two of the above-mentioned values. When the electrode group occupancy rate is within the above range, it is possible to suppress a decrease in characteristics such as repetitive charge and discharge characteristics and high-temperature storage characteristics accompanying an increase in internal pressure while ensuring the capacity of the electrochemical device, and further prevent the operation of the gas release valve.

[0140] Current collecting structure The current collector structure is not particularly limited. In some embodiments, the current collector structure is a structure that reduces the resistance of the wiring portion and the bonding portion. When the electrode group has the above-described laminated structure, a structure formed by bundling the metal core portions of each electrode layer and welding them to a terminal is preferably used. Since the internal resistance increases as the electrode area increases, it is also preferably used to provide two or more terminals in the electrode to reduce the resistance. When the electrode group has the above-described wound structure, by providing two or more lead wire structures on the positive electrode and the negative electrode respectively and bundling them to the terminal, the internal resistance can be lowered.

[0141] Outer package case The material of the outer package case is not particularly limited as long as it is a substance stable to the electrolytic solution used. The outer package case uses metals such as nickel-plated steel sheets, stainless steels, aluminum or aluminum alloys, magnesium alloys, or a laminated film of resin and aluminum foil, but is not limited thereto. In some embodiments, the outer package case is a metal of aluminum or aluminum alloy, or a laminated film.

[0142] The outer package case of metals includes, but is not limited to, a sealing structure formed by welding metals to each other by laser welding, resistance welding, or ultrasonic welding, or a rivet structure using the above-described metals via a resin gasket. The outer package case using the above-described laminated film includes, but is not limited to, a sealing structure formed by heat-sealing resin layers to each other. In order to improve the sealing property, a resin different from the resin used for the laminated film may be interposed between the above-described resin layers. When the resin layer is heat-sealed through the current collector terminal to form a sealed structure, since the metal bonds to the resin, a resin having a polar group or a modified resin into which a polar group is introduced is used as the interposed resin. Also, the shape of the outer package case is arbitrary, and may be any one of, for example, cylindrical, rectangular, laminated, button-type, large-sized, etc.

[0143] Protection element As a protective element, a positive temperature coefficient (PTC) whose resistance increases when abnormal heat generation or excessive current flows, a thermal fuse, a thermistor, a valve (current cutoff valve) that shuts off the current flowing through an electric circuit by rapidly increasing the internal pressure or internal temperature of the battery during abnormal heat generation, etc. are used. As the above-described protective element, an element that does not operate during normal use of high current may be selected, or it may be designed so that abnormal heat generation or thermal runaway does not occur even without a protective element.

[0144] [Application] The electrochemical device of the present invention includes any device in which an electrochemical reaction occurs, and specific examples thereof include all types of primary batteries, secondary batteries, fuel cells, solar cells, or capacitors. In particular, the electrochemical device is a lithium secondary battery including a lithium metal secondary battery, a lithium ion secondary battery, a lithium polymer secondary battery, or a lithium ion polymer secondary battery.

[0145] In some embodiments of the present invention, taking a lithium ion secondary battery as an example, a positive electrode sheet, a separator, and a negative electrode sheet are wound or laminated in order to form an electrode group, and then, for example, placed in an aluminum laminate and sealed, an electrolytic solution is injected, formation is performed, and sealing is performed to manufacture a lithium ion secondary battery. Next, performance measurement and cycle measurement are performed on the prepared lithium ion secondary battery. Those skilled in the art will understand that the preparation method of the electrochemical device (for example, a lithium ion battery) described above is only an example. Other methods generally used in the art can be used without departing from the content disclosed in the present invention.

[0146] The present invention further provides an electronic device including the electrochemical device according to the present invention.

[0147] The use of the electrochemical device of the present invention is not particularly limited and can be used in any electronic device known in the prior art. In some embodiments, the electrochemical device of the present invention is a notebook computer, a pen-input computer, a mobile computer, an e-book player, a mobile phone, a mobile fax, a mobile copy, a mobile printer, a headphone stereo, a video movie, a liquid crystal television, a handy cleaner, a portable CD, a mini disk, a transceiver, an electronic organizer, a calculator, a memory card, a portable tape recorder, a radio, a backup power supply, a motor, an automobile, a motorcycle, a motorized bicycle, a bicycle, a lighting fixture, a toy, a game device, a clock, a power tool, a strobe, a camera, a large household storage battery, a lithium ion capacitor, etc., but is not limited thereto.

[0148] Hereinafter, a lithium ion battery will be taken as an example, and the preparation of the lithium ion battery will be described with reference to specific examples. Those skilled in the art should understand that the preparation method described in the present invention is merely illustrative, and any other appropriate preparation method is within the scope of the present invention.

[0149] Hereinafter, examples and comparative examples of the lithium ion battery according to the present invention will be described to conduct performance evaluation.

[0150] Example 1 I. Preparation of Lithium Ion Battery 1. Preparation of Negative Electrode A first conductive agent and a first binder were mixed with deionized water at a mass ratio, stirred uniformly to obtain an undercoat slurry. The undercoat slurry was coated on a 12 μm copper foil and dried at 50 °C for 5 minutes. An active material, a second binder, and a second conductive agent were mixed with deionized water at a mass ratio, stirred uniformly to obtain a negative electrode active material slurry. The negative electrode active material slurry was coated on the undercoat layer. After drying and cold pressing, punching and tab welding were performed to obtain a negative electrode. The negative electrode was set to have corresponding compositions and parameters according to the conditions of the following examples and comparative examples.

[0151] 2. Preparation of Positive Electrode Lithium cobaltate as the positive electrode material, conductive material (Super-P), and polyvinylidene fluoride (PVDF) were mixed with N-methylpyrrolidone (NMP) at a mass ratio of 95%:2%:3%, stirred uniformly to obtain a positive electrode slurry. This positive electrode slurry was coated on a 12-μm aluminum foil, dried, cold pressed, punched, and tabs were welded to obtain a positive electrode.

[0152] 3. Preparation of Electrolyte In a dry argon gas atmosphere, EC, PC, PP, and DEC (weight ratio 1:1:1:1) were mixed, LiPF6 was added, and uniformly mixed to form a basic electrolyte. Here, the concentration of LiPF6 was 1.15 mol / L. The compound represented by the above formula 1 was added to the basic electrolyte by mass fraction, and the influence of its content relationship on the performance of the lithium-ion battery was studied.

[0153] 4. Preparation of Separator A polyethylene (PE) porous polymer film was used as the separator.

[0154] 5. Preparation of Lithium-Ion Battery The obtained positive electrode, separator, and negative electrode were wound in order and placed in an outer packaging foil, leaving an injection port. Electrolyte was injected from the injection port, sealed, and after processes such as formation and capacity measurement, a lithium-ion battery was obtained.

[0155] In Examples 2 to 6, the methods for preparing the positive electrode, electrolyte, separator, and lithium-ion battery were all the same as those in Example 1. The difference between Examples 2 to 6 and Example 1 was only that the composition of the undercoat layer in the negative electrode sheet was different.

[0156] In Comparative Example 1, the methods for preparing the positive electrode, electrolyte, separator, and lithium-ion battery were all the same as those in Examples 1 to 6. The difference between Comparative Example 1 and Examples 1 to 6 was only that the negative electrode of Comparative Example 1 did not contain an undercoat layer.

[0157] In Examples 7 to 9, the methods for preparing the positive electrode, the electrolyte, the separator, and the lithium-ion battery were all the same as those in Example 1. The differences between Examples 2 to 6 and Example 1 were only that the compositions of the undercoat layer and the negative electrode active material layer in the negative electrode sheet were different.

[0158] In Comparative Example 2, the methods for preparing the positive electrode, the electrolyte, the separator, and the lithium-ion battery were all the same as those in Examples 7 to 9. The difference between Comparative Example 2 and Examples 7 to 9 was only that the negative electrode of Comparative Example 2 did not contain an undercoat layer.

[0159] The specific negative electrode compositions of Examples 1 to 9 and Comparative Examples 1 to 2 are shown in Table 1 below.

[0160] The measurement methods for the performance parameters of the Examples and Comparative Examples were as follows.

[0161] II. Measurement Methods 1. Measurement Method for Adhesion (1) The dried electrode sheet was taken, and a sample with a width of 30 mm × a length of 100 to 160 mm was cut out with a blade. (2) A special double-sided tape was attached to the steel plate. The tape was 20 mm wide × 90 to 150 mm long. (3) The electrode sheet sample cut out in step (1) was attached to the double-sided tape with the measurement surface facing downward. (4) A paper tape with a width equal to the width of the electrode sheet sample and a length 80 to 200 mm longer than the length of the sample was inserted under the electrode sheet and fixed with masking tape. (5) The power of the three-thought tensile machine was turned on, the display lamp was lit, and the limit block was adjusted to an appropriate position for measurement.

[0162] 2. Electrode Measurement Method for Resistance (1) Electrode The resistance was measured using a device of INITIAL ENERGY SCIENCE&TECHNOLOGY (XIAMEN)Co.,Ltd, Electrode a resistance measuring instrument. (2) The power supply of the device was maintained at 220V, and the air pressure was greater than 0.7MPa. (3) The cut pole piece (60×80mm) was placed flat on the sample stage. (4) Next, the sample stage was placed inside the measurement chamber of the device, and the measurement was started. (5) During the entire test process, the measured air pressure was set to "0".

[0163] 3. Measurement method of cycle stability At 25°C, the lithium-ion battery was charged at a constant current of 1C until 4.45V, and then charged at a constant voltage until the current reached 0.05C at 4.45V. Next, it was discharged at a constant current of 1C until 3.0V, and the above operation was taken as the first cycle. Under the above conditions, the lithium-ion battery was cycled until the capacity retention rate after cycling reached 80%, and the number of cycles was recorded. "1C" was the value of the current that completely discharged the lithium-ion battery capacity within 1 hour. The capacity retention rate after cycling of the lithium-ion battery was calculated by the following formula. Capacity retention rate after cycling = (Discharge capacity corresponding to the number of cycles / Discharge capacity of the first cycle) × 100%

[0164] 4. Measurement method of deformation At 25°C, the lithium-ion battery was charged at a constant current of 1C until 4.45V, and then charged at a constant voltage until the current reached 0.05C at 4.45V. Next, it was discharged at a constant current of 1C until 3.0V, and the above operation was taken as the first cycle. The lithium-ion battery was cycled 500 times under the above conditions. "1C" was the value of the current that completely discharged the lithium-ion battery capacity within 1 hour. After cycling, the battery was disassembled, the negative electrode piece was taken out, and the presence or absence of decarbonization of the film piece was observed. If there was decarbonization, it was deformed; if there was no decarbonization, it was not deformed.

[0165] 5. Measurement method of porosity All measurement methods of the porosity of the pole piece adopted a mercury porosimeter, and the specific operation was as follows. A sample was taken using an electrode plate whose one-sided surface completely covered the film piece. The density and porosity of the sample were estimated, and an appropriate dilatometer was selected. The sample was first placed in an oven and dried for 2 hours to remove moisture. The weight of the sample was measured before analysis. The sample was loaded into the dilatometer, weighed after sealing, which was the weight of the sample + dilatometer. The dilatometer was loaded into the low-pressure station, and the low-pressure file was edited to start the low-pressure analysis. After the low-pressure analysis was completed, the dilatometer was taken out and weighed, which was the weight of the sample + dilatometer + mercury. The dilatometer was attached to the high-pressure station. After fixing the dilatometer, the head of the high-pressure bottle was screwed in until it reached the bottom to remove air bubbles. The high-pressure analysis was started, and the vent valve was loosened or tightened according to the instructions. After the high-pressure analysis was completed, the dilatometer was taken out, cleaned, and the measurement was ended. What was measured at this time was the porosity X of the electrode plate. The method for converting the porosity X of the electrode plate to the porosity V of the film piece was as follows. Ten locations were randomly selected from the surface of the electrode plate, and the average thickness H of the electrode plate was measured. The film piece on the surface of the electrode plate was washed away using an organic solvent. Ten locations were randomly selected from the surface of the current collector, and the average thickness h of the current collector was measured. Porosity V of the film piece = Porosity X of the electrode plate × H / (H - h)

[0166] 6. Measurement method of rate performance At 25°C, the lithium-ion battery was charged at a constant current of 1C to 4.45V, then charged at a constant voltage of 4.45V until the current reached 0.05C, left standing for 5 minutes, and then discharged at a constant current of 0.2C to the cut-off voltage of 3V. At this time, the actual discharge capacity was recorded as D0. Next, it was charged at a constant current of 1C to 4.45V, further charged at a constant voltage of 4.45V until the current reached 0.05C, and finally discharged at 2C to the cut-off voltage of 3V. The actual discharge capacity at this time was recorded as D1. Rate characteristics of lithium-ion battery = [(D1 - D0) / D0] × 100%

[0167] 7. Method for measuring average particle diameter of particulate conductive agent The sample was spread on a sample stage, and after taking a photograph of the sample with a scanning electron microscope (SEM) or a transmission electron microscope (TEM), 10 particulate conductive agents were randomly selected from the SEM or TEM photograph using image analysis software. The area of each of these particulate conductive agents was determined. Next, assuming that the particulate conductive agent is spherical, the particle diameter R (diameter) of each was determined by the following formula. R = 2 × (S / π) 1 / 2 (Here, S is the area of the particulate conductive agent.)

[0168] For three SEM or TEM images, the process of determining the particle diameter R of the particulate conductive agent was performed, and the particle diameters of the 30 (10 × 3) particulate conductive agents obtained were arithmetically averaged to obtain the average particle diameter D of the particulate conductive agent.

[0169] 8. Method for measuring average diameter of tubular conductive agent The sample was spread on a sample stage, and after taking a photograph of the sample with a scanning electron microscope (SEM) or a transmission electron microscope (TEM), 10 tubular conductive agents were randomly selected from the SEM or TEM photograph using image analysis software. Five points were arbitrarily selected from the tube walls on both sides of the photograph of each tubular conductive agent, and perpendicular lines were drawn at each point along the stretching direction perpendicular to the tube wall. The average distance to the intersection with the other tube wall was the tube diameter R of the tubular conductive agent. For three SEM or TEM images, the process of determining the tube diameter R of the tubular conductive agent was performed, and the tube diameters of the 30 (10 × 3) tubular conductive agents obtained were arithmetically averaged to obtain the average tube diameter D of the tubular conductive agent.

[0170] III. Measurement results Table 1 shows the composition, adhesive strength, of the negative electrode sheets in Examples 1 to 9 and Comparative Examples 1 to 2 ElectrodeShows the resistance and the performance of the corresponding lithium-ion battery. The compression density PD was 1.30 g / cm 3 in all cases.

[0171]

Table 1

[0172] As can be seen from the data in Table 1, Examples 1-9 with an undercoat layer have significantly improved adhesion compared to Comparative Examples 1-2 without an undercoat layer. Correspondingly, their cycle and shape stability have also been significantly improved. The reason is that, on the one hand, the presence of the undercoat layer improves the surface defects of the copper foil, improves the riveting joining effect between the active material layer and the electrode tab, increases the adhesion between the undercoat layer and the copper foil, thereby improving the adhesion between the entire film piece and the current collector and reducing the risk of film piece detachment. On the other hand, the presence of the undercoat layer can play a good buffering role. When the negative electrode active material is inserted and expanded by lithium ions, the undercoat layer avoids the expanded active material from directly applying a force to the surface of the current collector. If a direct force is applied to the surface of the current collector, the current collector in that direction cannot be fixed and displaced, so the active material can only expand on the outer surface of the film piece as a whole. When releasing lithium ions and contracting, each part of the active material tends to contract synchronously, or the inner part with higher electronic conductivity may contract faster, and the active material in close contact with the original surface of the current collector separates from the current collector, causing the film piece to fall off, increasing the internal resistance, and deteriorating the cycle performance. Furthermore, Examples 2, 6-9 using an undercoat layer binder with polar functional groups (carboxyl groups) can significantly improve the adhesion between the film piece and the current collector, and the shape stability of the electrode tab is more stable. In particular, Examples 7-9 using an undercoat layer binder with carboxyl groups can ensure an adhesion of 500 N / m or more and maintain excellent shape stability even for high-expansion Si-based active materials.

[0173] As can be seen from the comparison between FIGS. 3 and 4, the shape stability of the negative electrode sheet provided in Example 1 of the present invention is significantly improved as compared with the shape stability of the negative electrode sheets of Comparative Examples 1 and 2.

[0174] The differences between Examples 10 to 14 and Example 2 are only that the compression density (represented by consolidation) of the film pieces of the negative electrode and the porosity of the film pieces are different.

[0175] Table 2 shows the composition of the same negative electrode film pieces, different consolidations, the corresponding porosities of the film pieces, and the cycle characteristics and rate characteristics of the corresponding lithium-ion batteries in Examples 2, 10 to 14.

[0176]

Table 2

[0177] As can be seen from the data in Table 2, Examples 2, 10 to 13 in which the compression density of the film pieces is 1.30 to 1.80 g / cm 3 have better cycle stability and rate characteristics than Example 14 in which the consolidation is 1.83 g / cm 3 . On the one hand, the examples in which the consolidation is 1.30 to 1.80 g / cm 3 provide an appropriate porosity, can buffer the volume expansion and contraction due to the insertion and desorption of lithium ions during cycling, and can reduce the risk of the peeling of the electrode sheet. On the other hand, appropriate consolidation also reduces the pressure on the undercoat layer, ensures the presence of the undercoat layer between the active material layer and the current collector, and avoids the undercoat layer being pushed into the gaps of the active material layer by too high pressure, thereby avoiding the undercoat layer not fulfilling the riveting joining and buffering functions. Also, due to the excellent porosity, it can be in sufficient contact with the electrolyte, ensuring that the battery has better rate characteristics.

[0178] The differences between Examples 15 to 23 and Example 4 are only that the ratio of the particle size of the first conductive agent (SP) to the thickness of the undercoat layer in the undercoat layer of the negative electrode sheet is different. The differences between Examples 24 to 32 and Example 2 are only that the ratio of the tube diameter of the first conductive agent (CNT) to the thickness of the undercoat layer in the undercoat layer of the negative electrode is different.

[0179] Table 3 shows, in Examples 15 to 30, that the compositions are the same as those of Example 4 (SP) and Example 2 (CNT) respectively, and the relationship between the average particle diameter of the first conductive agent particles / the average diameter of the tubes and the thickness of the undercoat layer in the undercoat layer is related to the adhesion of the corresponding electrode sheet, Electrode resistance, and the influence on the cycle stability of the corresponding lithium-ion battery.

[0180]

Table 3

[0181] As can be seen from the data in Table 3, Examples 16 to 19, 21 to 23, and 25 to 31 in which D / H is in the range of 0.5 to 1.25 have better Electrode resistance and cycle stability compared to Examples 15, 20, 24, and 32 in which D / H is outside the above range. On the one hand, an appropriate particle size (tube diameter) / thickness of the undercoat layer can avoid the lamination between too many small particle conductive agents in the undercoat layer, avoid the existence of too much interfacial resistance, and further Electrode reduce the resistance and improve the cycle stability. On the other hand, too large a particle size (tube diameter) / thickness of the undercoat layer results in non-uniform distribution of the conductive agent in the undercoat layer, and further Electrode results in an increase in resistance.

[0182] The differences between Examples 33 to 37 and Example 2 are that the electrolytic solution contains a compound containing an S=O double bond represented by Formula 1, and the mass fraction y of the compound containing an S=O double bond in the electrolytic solution and the porosity V of the film piece satisfy a certain relationship.

[0183] Table 4 shows the influence of the relationship between the mass fraction y of the compound containing the S=O double bond in the electrolyte and the porosity V of the film pieces on the electrochemical performance of the lithium-ion battery in Examples 2 and 33 to 37.

[0184]

Table 4

[0185] As can be seen from the data in Table 4, by satisfying the relational expression 0.01 ≦ y / V ≦ 0.07 for the content of the compound containing the S=O double bond and the porosity of the film pieces, the cycle stability and rate performance are significantly improved. This is because an appropriate amount of the compound containing the S=O double bond represented by Formula 1 further forms a complete and stable high-ion-conducting solid electrolyte film on the surface of the electrode, thereby further improving the ionic conductivity and improving the rate performance. If the amount of the compound containing the S=O double bond represented by Formula 1 is too large, that is, y / V > 0.07, the formed solid electrolyte film is too thick and is disadvantageous for the transport of lithium ions.

[0186] Throughout the specification, a reference by "Example", "a part of an example", "one example", "another example", "example", "specific example", or "a part of an example" means that at least one example or example of the present invention includes the specific features, structures, materials, or characteristics described in the example or example. Therefore, references described at various places throughout the specification, such as "in some examples", "in an example", "in one example", "in other examples", "in one example", "in a specific example", or "example", do not necessarily refer to the same example or example in the present invention. Also, the specific features, structures, materials, or characteristics of the present specification can be combined in any suitable manner in one or more examples or examples.

[0187] Exemplary embodiments have been disclosed and described, and those skilled in the art should understand that the above-described embodiments should not be construed as limiting the present invention, and that modifications, substitutions, and changes to the embodiments are possible without departing from the technical idea, principle, and scope of the present invention.

Claims

1. An electrode tab including a current collector and a film piece, wherein the film piece includes an undercoat layer provided on the surface of the current collector and an active material layer provided on the surface of the undercoat layer, the undercoat layer includes a first binder and a first conductive agent, the adhesion between the film piece and the current collector is ≧20 N / m, The compression density of the film piece is 1.30 g / cm ３ to 1.80 g / cm ３ and the porosity of the film piece is 20% to 50%, the mass content of the first binder in the undercoat layer is 40% to 95%, the mass content of the first conductive agent in the undercoat layer is 5% to 60%, the first conductive agent includes at least one of conductive carbon black, ketjen black, single-walled carbon nanotubes, and multi-walled carbon nanotubes, and is characterized by an electrode tab.

2. (1) The thickness of the undercoat layer is 100 nm to 2 μm, and (2) when the average particle diameter of the particles of the first conductive agent or the average diameter of the tubes is D, and the thickness of the undercoat layer is H, the ratio D / H of D to H is 0.25 to 1.5, and The electrode tab according to claim 1, characterized by having at least one of the features.

3. a. The adhesion between the film piece and the current collector is ≧80 N / m, and d. The resistance of the electrode tab is 3 mΩ to 50 mΩ, and The electrode tab according to claim 1, characterized by having at least one of the features.

4. f. The first binder includes at least one of a carbon-carbon double bond, a carboxyl group, a carbonyl group, a carbon-nitrogen single bond, a hydroxyl group, an ester group, an acyl group, and an aryl group, and g. The first binder includes at least one of styrene-butadiene rubber, polyacrylic acid, polyvinylpyrrolidone, and polyacrylamide, and The electrode tab according to claim 1, characterized by having at least one of the features.

5. (3) The thickness of the undercoat layer is 100 nm to 1000 nm, and (4) when the average particle diameter of the particles of the first conductive agent or the average diameter of the tubes is D, and the thickness of the undercoat layer is H, the ratio D / H of D to H is 0.5 to 1.25, and The electrode tab according to claim 1, characterized by having at least one of the features.

6. The active material layer contains an active material and a second binder, and the active material layer i. The active material includes at least one of a graphite-based material and a silicon-based material, and the silicon-based material includes at least one of silicon, silicon oxide, silicon carbon composite, and silicon alloy; j. The active material layer contains, by mass content, 80% to 99% of the active material, 0.8% to 20% of the second binder, and 0 to 5% of the second conductive agent; The electrode tab according to claim 1, characterized by having at least one of the above features.

7. An electrochemical device including a positive electrode tab, a negative electrode tab, and a separator provided between the positive electrode tab and the negative electrode tab, The electrochemical device, characterized in that the negative electrode tab is the electrode tab according to any one of claims 1 to 6.

8. The electrochemical device includes an electrolytic solution, The electrolytic solution includes a compound containing an S=O double bond. The electrochemical device according to claim 7.

9. The electrochemical device k. The compound containing an S=O double bond includes at least one of a cyclic sulfate ester, a chain sulfate ester, a chain sulfonate ester, a cyclic sulfonate ester, a chain sulfite ester, and a cyclic sulfite ester; l. The compound containing an S=O double bond includes at least one of the compounds represented by Formula 1; having at least one of the above features, 【Chemical 1】 W is 【Chemical 2】 selected from L is selected from a single bond or a methylene group, m is an integer from 1 to 4, n is an integer from 0 to 2, and p is an integer from 0 to 6. The electrochemical device according to claim 8.

10. When the mass fraction of the compound containing an S=O double bond in the electrolytic solution is y and the porosity of the film piece is V, y and V satisfy the relational expression 0.01 ≤ y / V ≤ 0.

07. The electrochemical device according to claim 9.

11. An electronic device, characterized by including the electrochemical device according to any one of claims 7 to 10.

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