Lithium-ion secondary battery
Patent Information
- Authority / Receiving Office
- JP · JP
- Patent Type
- Applications
- Filing Date
- 2025-04-07
- Publication Date
- 2026-01-02
AI Technical Summary
Lithium-ion secondary batteries with silicon oxide-based active materials face challenges in charge-discharge characteristics due to the expansion and contraction of these materials during charging and discharging, leading to microcracks and reduced performance.
A negative electrode structure with a two-layer active material layer configuration, where the second layer contains a higher weight fraction of Si-based particles, carbon nanotubes, or amorphous carbon, and possibly harder graphite, to manage the expansion and contraction, facilitating electrolyte penetration and improving charge-discharge characteristics.
The proposed electrode structure enhances the charge-discharge performance by allowing easier electrolyte penetration and reducing microcracks, thereby improving the overall battery performance.
Abstract
Description
Lithium-ion secondary battery
[0001] The present disclosure relates to lithium-ion secondary batteries.
[0002] Lithium ion secondary batteries and the like are used as power sources for electric vehicles (EVs), hybrid vehicles (HVs), and the like, or as stationary power sources. Known lithium ion secondary batteries include those having a negative electrode with multiple active material layers.
[0003] Patent Document 1 discloses a negative electrode for a secondary battery, which includes a current collector, a first negative electrode active material layer formed on the current collector and containing a first active material, and a second negative electrode active material layer formed on the first negative electrode active material layer and containing a second active material, in which the second active material is a bimodal active material made up of active materials having different specific surface areas, the first and second active materials including natural graphite, artificial graphite, etc., and at least one of the first and second negative electrode active material layers further including a silicon oxide-based active material (SiOx (0<x<2)), and the content of the silicon oxide-based active material in the upper layer (second negative electrode active material layer) is more than twice the content in the lower layer (first negative electrode active material layer).
[0004] Japanese Patent Application Laid-Open No. 2022-74046
[0005] The silicon oxide-based active material used in the negative electrode for secondary batteries described in Patent Document 1 may expand and contract during charge and discharge.
[0006] Therefore, there is a demand for improving the charge-discharge characteristics of a negative electrode containing a silicon oxide-based active material.
[0007] The purpose of the present disclosure is to provide a silicon oxide-based active material, SiO ｘ The object of the present invention is to improve the charge-discharge characteristics of a lithium ion secondary battery having a negative electrode containing Si-based particles containing (0<x<2) or the like.
[0008] The lithium-ion secondary battery according to the present disclosure includes a positive electrode and a negative electrode. The negative electrode includes a negative electrode current collector and a negative electrode active material layer laminated on the negative electrode current collector. The negative electrode active material layer includes a first negative electrode active material layer laminated on the negative electrode current collector and a second negative electrode active material layer laminated on the first negative electrode active material layer. The first negative electrode active material layer and the second negative electrode active material layer contain Si-based particles, and the weight fraction of the Si-based particles in the second negative electrode active material layer is greater than the weight fraction of the Si-based particles in the first negative electrode active material layer. The negative electrode active material layer has at least one of the following configurations (1) to (4).
[0009] Configuration (1): The first negative electrode active material layer and the second negative electrode active material layer contain carbon nanotubes, and the weight fraction of the carbon nanotubes in the second negative electrode active material layer is greater than the weight fraction of the carbon nanotubes in the first negative electrode active material layer.
[0010] Configuration (2): The first and second negative electrode active material layers contain a binder, and the weight fraction of the binder in the second negative electrode active material layer is greater than the weight fraction of the binder in the first negative electrode active material layer.
[0011] Configuration (3): The first negative electrode active material layer and the second negative electrode active material layer contain amorphous carbon, and the weight fraction of amorphous carbon in the second negative electrode active material layer is greater than the weight fraction of amorphous carbon in the first negative electrode active material layer.
[0012] Configuration (4): The first negative electrode active material layer and the second negative electrode active material layer contain graphite as a main component, and the hardness of the graphite in the first negative electrode active material layer is greater than the hardness of the graphite in the second negative electrode active material layer.
[0013] According to the present disclosure, silicon oxide-based active materials such as SiO ｘ The charge-discharge characteristics of a lithium ion secondary battery having a negative electrode containing Si-based particles containing (0<x<2) or the like can be improved.
[0014] Fig. 4 is an external perspective view showing a lithium ion secondary battery of an embodiment. Fig. 5 is a perspective view showing a charge / discharge body built into the lithium ion secondary battery 1 of Fig. 1. Fig. 6 is a perspective view showing a partially developed charge / discharge body 100 of Fig. 2. Fig. 7 is a schematic partially enlarged cross-sectional view showing the negative electrode 120 of Fig. 3. Fig. 8 is a schematic partially enlarged cross-sectional view showing another form of the negative electrode 120 of Fig. 3.
[0015] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. In each drawing, the size and proportions of components may be exaggerated to facilitate understanding of the embodiments. In each drawing, the same components are assigned the same reference numerals. In each drawing, the width direction X, depth direction Y, and height direction Z of the lithium ion secondary battery and its components are indicated by arrows. However, in each drawing, the width direction X, depth direction Y, and height direction Z indicate relative directional relationships. That is, for example, if the lithium ion secondary battery is rotated 180 degrees and placed with its top and bottom faces reversed, or if the lithium ion secondary battery is rotated 90 degrees and placed with its top face facing sideways, the width direction X, depth direction Y, and height direction Z of the lithium ion secondary battery will change.
[0016] (Configuration of Lithium-Ion Secondary Battery Having Positive Electrode of Embodiment) The configuration of a lithium-ion secondary battery having a positive electrode of the embodiment will be described with reference to FIGS. 1 to 4. FIG.
[0017] FIG. 1 is a perspective view showing the appearance of a lithium ion secondary battery according to an embodiment.
[0018] In this figure, the lithium-ion secondary battery 1 has a configuration in which a charging / discharging element (not shown) is housed in a container formed by a case 201 and a lid 202. A positive electrode terminal 301 and a negative electrode terminal 302 are attached to the lid 202 in an insulated state. The lid 202 is joined to the opening of the case 201 and, together with the case 201, seals the charging / discharging element.
[0019] When a battery pack is constructed using multiple lithium ion secondary batteries 1, the positive electrode terminal 301 of adjacent lithium ion secondary batteries 1 is joined to the negative electrode terminal 302 of another adjacent lithium ion secondary battery 1 via a bus bar.
[0020] FIG. 2 is a perspective view showing a charging / discharging element built into the lithium ion secondary battery 1 of FIG.
[0021] The charge / discharge unit 100 shown in Fig. 2 has a configuration in which a separator is sandwiched between a positive electrode and a negative electrode and wound up. The charge / discharge unit 100 has a positive electrode tab 111b and a negative electrode tab 121b. The positive electrode tab 111b is connected to the positive electrode terminal 301 in Fig. 1. The negative electrode tab 121b is connected to the negative electrode terminal 302 in Fig. 1.
[0022] The charging / discharging unit 100 is sealed in the lithium-ion secondary battery 1 of FIG. 1 , and an electrolytic solution (electrolyte) is poured into the charging / discharging unit 100 through a pouring port provided in the lid 202. This causes the charging / discharging unit 100 to be immersed in the electrolytic solution. After the electrolytic solution is poured, the pouring port is sealed with a pouring stopper. The electrolytic solution contains an organic solvent, a supporting salt, and an additive. For example, a carbonate ester is used as the organic solvent. For example, a lithium salt is used as the supporting salt. The additive contains a material for forming a negative electrode film. For example, the material for forming the negative electrode film is vinylene carbonate.
[0023] FIG. 3 is a perspective view showing the charge / discharge body 100 of FIG. 2 in a partially developed state.
[0024] 3, the positive electrode 110, negative electrode 120, and separator 130 that constitute the charge / discharge body are each formed in a long strip shape extending in the X-axis direction. The positive electrode 110 is provided with a positive electrode tab 111b. The negative electrode 120 is provided with a negative electrode tab 121b. The positive electrode tab 111b and the negative electrode tab 121b protrude in the same direction (positive direction of the Z-axis).
[0025] A separator 130 is sandwiched between the positive electrode 110 and the negative electrode 120. Furthermore, to prevent direct contact between the positive electrode 110 and the negative electrode 120 when they are wound, another separator 130 is disposed on the opposite side of the negative electrode 120. In other words, in this figure, the negative electrode 120 is sandwiched between two separators 130. The separator 130 insulates the positive electrode 110 from the negative electrode 120. The separator 130 allows lithium ions to pass through via the electrolyte.
[0026] The negative electrode current collecting portion of the negative electrode 120 has a greater width in the short side direction (Z-axis direction) than the positive electrode current collecting portion of the positive electrode 110. The separator 130 has a greater width in the short side direction (Z-axis direction) than the positive electrode 110 and the negative electrode 120.
[0027] The positive electrode current collecting layer of the positive electrode 110 is made of, for example, an aluminum alloy. The separator 130 is made of a porous material such as polyethylene (PE), polypropylene (PP), or the like.
[0028] FIG. 4 is a schematic partial enlarged cross-sectional view showing the negative electrode 120 of FIG.
[0029] 4, the negative electrode 120 includes a negative electrode current collecting layer 121 (negative electrode current collector), a first negative electrode active material layer 122, and a second negative electrode active material layer 123. The first negative electrode active material layer 122 and the second negative electrode active material layer 123 are formed in this order on one surface (the upper surface in the figure) of the negative electrode current collecting layer 121. That is, the negative electrode 120 includes a plurality of active material layers.
[0030] The negative electrode current collecting layer 121 is made of, for example, a copper alloy.
[0031] The first negative electrode active material layer 122 corresponds to the lower layer of the two active material layers when the negative electrode current collecting layer 121 is used as a reference.
[0032] The first negative electrode active material layer 122 includes graphite particles 122a, Si-based particles 122b, carbon nanotubes (CNTs) 122c, and a binder 122d.
[0033] The second negative electrode active material layer 123 corresponds to the upper layer of the two active material layers when the negative electrode current collecting layer 121 is used as a reference.
[0034] The second negative electrode active material layer 123 includes graphite particles 123a, Si-based particles 123b, carbon nanotubes (CNTs) 123c, and a binder 123d.
[0035] The second negative electrode active material layer 123 has a higher content of Si-based particles 123b than the first negative electrode active material layer 122. The content of binder 123d in the second negative electrode active material layer 123 is preferably equal to or relatively greater than the content of binder 122d in the first negative electrode active material layer 122. The content of carbon nanotubes 123c in the second negative electrode active material layer 123 is preferably equal to or relatively greater than the content of carbon nanotubes 122c in the first negative electrode active material layer 122.
[0036] 4, when the content of Si-based particles in the upper layer (second negative electrode active material layer) is high, the upper layer is more likely to accept lithium ions, improving the input / output characteristics. On the other hand, when the content of Si-based particles in the lower layer (first negative electrode active material layer) is high, the Si-based particles are less likely to react with the electrolyte, improving the charge / discharge cycle characteristics.
[0037] The positive electrode 110 shown in FIG. 3 includes a positive electrode current collector and a positive electrode active material layer laminated on the positive electrode current collector. The positive electrode active material layer may be a single layer, or may include a first positive electrode active material layer laminated on the positive electrode current collector and a second positive electrode active material layer laminated on the first positive electrode active material layer. The single layer includes a positive electrode active material, a conductive additive, and a positive electrode binder. In the case of a configuration including a first positive electrode active material layer and a second positive electrode active material layer laminated on the first positive electrode active material layer, the first positive electrode active material layer includes the first positive electrode active material, the first conductive additive, and the first positive electrode binder. The second positive electrode active material layer includes the second positive electrode active material, the second conductive additive, and the second positive electrode binder.
[0038] The positive electrode active material, the first positive electrode active material, and the second positive electrode active material constituting the single layer are composed of a lithium-containing composite oxide. The lithium-containing composite oxide contains, for example, lithium and a metal element such as nickel, cobalt, or manganese. The first conductive additive is also called a "first conductive material," and the second conductive additive is also called a "second conductive material."
[0039] Next, methods for measuring the particle composition, particle size, and specific surface area will be described.
[0040] <Method of measuring negative electrode active material, etc.> The average composition of the particles of the negative electrode active material can be confirmed by inductively coupled plasma (ICP), atomic absorption spectrometry (AAS), etc. The average particle size of the primary particles of the negative electrode active material was determined by using a scanning electron microscope (SEM) to draw a straight line in a predetermined direction on a cross-sectional observation image of the secondary particles, and dividing the length of the cross-sectional line by the number of primary particles contained in the cross-sectional line to calculate the particle size of the primary particles. The average value obtained using 10 secondary particles was used as the average particle size of the primary particles. Note that the straight line in the predetermined direction refers to a straight line extending until the sequence of primary particles is discontinued, taking into account the presence of voids or the like in the cross-section of the secondary particles, and is referred to as a "cross-sectional line." The average particle size of the particles in the raw material slurry and the secondary particles of the negative electrode active material can be measured, for example, by a laser diffraction particle size distribution analyzer, etc. The BET specific surface area can be calculated by a gas adsorption method using an automatic specific surface area analyzer.
[0041] The average particle size of the graphite particles 122a and 123a is preferably 5 μm or more and 25 μm or less. The average particle sizes of the graphite particles 122a and 123a may be approximately the same or different. When the average particle sizes of the graphite particles 122a and 123a are different, the average particle size of the graphite particles 122a may be, for example, 15 μm or more and 25 μm or less, while the average particle size of the graphite particles 123a may be, for example, 5 μm or more and 10 μm or less. Conversely, the average particle size of the graphite particles 123a may be, for example, 15 μm or more and 25 μm or less, while the average particle size of the graphite particles 122a may be, for example, 5 μm or more and 10 μm or less.
[0042] The average particle size of the positive electrode active material can also be measured using the above-mentioned method for measuring the average particle sizes of the primary particles and secondary particles of the negative electrode active material.
[0043] The amount of the residual alkaline component in the positive electrode active material can be calculated by neutralization titration. The positive electrode active material can be compressed using a press, an autograph, or the like.
[0044] The graphite particles 122a and 123a may be graphitizable carbon or non-graphitizable carbon. Graphitizable carbon corresponds to soft carbon. Non-graphitizable carbon corresponds to hard carbon.
[0045] The first negative electrode active material layer 122 and the second negative electrode active material layer 123 may contain amorphous carbon. Examples of amorphous carbon include acetylene black and carbon black. The amorphous carbon includes low-crystalline carbon.
[0046] The graphite particles 122a and 123a may be pitch-coated natural graphite, non-pitch-coated natural graphite, artificial graphite, etc. Pitch-coated natural graphite is harder than non-pitch-coated natural graphite. The natural graphite is composed of multiple layers, and the ends of the multiple layers along the stacking direction are not coated with resin. The resin contains, for example, electrically conductive carbon.
[0047] The Si-based particles 122b and the Si-based particles 123b are Si or SiO ｘ (0<x<2) particles, Si or SiO ｘ (0<x<2). Such particles include, for example, silicon oxide (Li—SiO ｘ (0<x<2) is preferably used. The Si-based particles may be not only oxides of silicon (Si) but also silicon compounds containing other anions. In this specification, such oxides and silicon compounds are collectively referred to as "Si-containing compounds." Furthermore, Si particles and particles of Si-containing compounds are collectively referred to as "Si-based particles."
[0048] The binder 122d and the binder 123d include, for example, one or more of a rubber-based material, an acrylic-based material, a polyamide-imide material, and a polyimide material.
[0049] (Configuration of negative electrodes of Examples 1 to 7 and Comparative Example 1 and effects of the configuration) In the negative electrodes of Examples 1 to 7 and Comparative Example 1, the negative electrode active material layer has a two-layer structure of a first negative electrode active material layer (lower layer) and a second negative electrode active material layer (upper layer).
[0050] The first negative electrode active material layer and the second negative electrode active material layer contain Si-based particles, and the weight fraction of the Si-based particles in the second negative electrode active material layer is greater than the weight fraction of the Si-based particles in the first negative electrode active material layer.
[0051] The negative electrode active material layer has at least one of the following structures (1) to (4).
[0052] Configuration (1): The first and second negative electrode active material layers contain CNTs, and the weight fraction of CNTs in the second negative electrode active material layer is greater than the weight fraction of CNTs in the first negative electrode active material layer.
[0053] Configuration (2): The first and second negative electrode active material layers contain a binder, and the weight fraction of the binder in the second negative electrode active material layer is greater than the weight fraction of the binder in the first negative electrode active material layer.
[0054] Configuration (3): The first negative electrode active material layer and the second negative electrode active material layer contain amorphous carbon, and the weight fraction of amorphous carbon in the second negative electrode active material layer is greater than the weight fraction of amorphous carbon in the first negative electrode active material layer.
[0055] Configuration (4): The first negative electrode active material layer and the second negative electrode active material layer contain graphite as a main component, and the hardness of the graphite in the first negative electrode active material layer is greater than the hardness of the graphite in the second negative electrode active material layer.
[0056] The Si-based particles cause microcracks in the active material layer due to expansion and contraction, which allows the electrolyte to easily penetrate, thereby improving charge-discharge characteristics.
[0057] According to the configuration (1), the expansion of the first negative electrode active material layer (lower layer) is less likely to be hindered, which allows the electrolyte to easily penetrate therethrough, thereby improving the charge-discharge characteristics.
[0058] According to the configuration (2), the expansion of the first negative electrode active material layer (lower layer) is less likely to be hindered, which allows the electrolyte to easily penetrate therethrough, thereby improving the charge-discharge characteristics.
[0059] According to the configuration (3), the electrolyte solution can easily permeate into the first negative electrode active material layer (lower layer), thereby improving the charge-discharge characteristics.
[0060] According to the configuration (4), fine cracks are more likely to occur in the first negative electrode active material layer (lower layer), which allows the electrolyte to penetrate more easily, thereby improving the charge-discharge characteristics.
[0061] (Configuration of negative electrodes of Examples 8 to 14 and Comparative Example 2 and effects of the configuration) In the negative electrodes of Examples 8 to 14 and Comparative Example 2, the negative electrode active material layer also has a two-layer structure of a first negative electrode active material layer (lower layer) and a second negative electrode active material layer (upper layer).
[0062] The first negative electrode active material layer and the second negative electrode active material layer contain Si-based particles, and the weight fraction of the Si-based particles in the first negative electrode active material layer is greater than the weight fraction of the Si-based particles in the second negative electrode active material layer.
[0063] The negative electrode active material layer has at least one of the following structures (5) to (8).
[0064] Configuration (5): The first and second negative electrode active material layers contain CNTs, and the weight fraction of CNTs in the second negative electrode active material layer is smaller than the weight fraction of CNTs in the first negative electrode active material layer.
[0065] Configuration (6): The first and second negative electrode active material layers contain a binder, and the weight fraction of the binder in the second negative electrode active material layer is smaller than the weight fraction of the binder in the first negative electrode active material layer.
[0066] Configuration (7): The first negative electrode active material layer and the second negative electrode active material layer contain amorphous carbon, and the weight fraction of amorphous carbon in the second negative electrode active material layer is smaller than the weight fraction of amorphous carbon in the first negative electrode active material layer.
[0067] Configuration (8): The first negative electrode active material and the second negative electrode active material contain graphite as a main component, and the hardness of the graphite in the second negative electrode active material layer is greater than the hardness of the graphite in the first negative electrode active material layer.
[0068] The Si-based particles cause microcracks in the active material layer due to expansion and contraction.
[0069] These fine cracks allow the electrolyte to easily penetrate, improving the charge-discharge characteristics.
[0070] According to the configuration (5), the expansion of the second negative electrode active material layer (upper layer) is less likely to be hindered, which allows the electrolyte to easily penetrate therethrough, thereby improving the charge-discharge characteristics.
[0071] According to the configuration (6), the expansion of the second negative electrode active material layer (upper layer) is less likely to be hindered, which allows the electrolyte to penetrate more easily and improves the charge-discharge characteristics.
[0072] According to the configuration (7), the electrolyte solution can easily permeate into the second negative electrode active material layer (upper layer), thereby improving the charge-discharge characteristics.
[0073] According to the configuration (8), fine cracks are more likely to occur in the second negative electrode active material layer (upper layer), which allows the electrolyte to penetrate more easily, thereby improving the charge-discharge characteristics.
[0074] The configurations of the example and the comparative example will be described with reference to FIG.
[0075] The first negative electrode active material layer 124 is a lower layer and includes graphite particles 124a, Si-based particles 124b, carbon nanotubes 124c (CNTs), and a binder 124d.
[0076] The second negative electrode active material layer 125 is an upper layer and includes graphite particles 125a, Si-based particles 125b, carbon nanotubes (CNTs) 125c, and a binder 125d.
[0077] The Si-based particles 124b and the Si-based particles 125b are SiO. The weight fractions of the Si-based particles 124b and the Si-based particles 125b are calculated based on the weight of SiO.
[0078] A predetermined compressive load is applied to each of the graphite particles 124a and the graphite particles 125a.
[0079] Binder 124d and binder 125d are mixtures of styrene butadiene rubber (SBR), polyacrylic acid (PAA) and carboxymethyl cellulose (CMC).
[0080] Table 1 summarizes Examples 1 to 7 and Comparative Example 1, in which the weight fraction of SiO contained in the second negative electrode active material layer is relatively large. Here, the weight fraction is the proportion, expressed as a percentage, of the graphite particles, Si-based particles, CNTs, binder, etc., which are the negative electrode active materials constituting the negative electrode active material layer. In other words, the weight fraction is the proportion, expressed as a percentage, of the graphite particles, Si-based particles, CNTs, binder, etc., relative to the total weight of the positive electrode active material layer. The unit of weight fraction is "wt%" (weight %). The particle size is the average particle size of the primary particles.
[0081]
[0082] This table shows the weight fractions of SiO, CNT, and binder, which are examples of Si-based particles, the compressive load required to make the density of graphite 1.7 g / cc, which corresponds to the hardness of the graphite particles, the weight fraction of added acetylene black, and the percentage of the charge rate ratio (3 C charge rate) / (0.2 C charge rate). Note that since the binder is a mixture of three types, the weight fraction of the mixture is listed at the top, and below that, the weight fractions of SBR, PAA, and CMC that make up the mixture are listed for each example and comparative example.
[0083] Specifically, the weight fraction of SiO is 25-35 wt% in the upper layer and 5-15 wt% in the lower layer. The weight fraction of CNT is 0.10-0.17 wt% in the upper layer and 0.03-0.10 wt% in the lower layer. The weight fraction of binder is 5-8 wt% in the upper layer and 2-5 wt% in the lower layer. The compressive load of graphite is 1.5-2.5 kN / cm in the upper layer. ２ , lower layer: 2.5 to 3.5 kN / cm ２ The weight fraction of acetylene black is 2.0 to 3.5 wt % in the upper layer and 0.5 to 2.0 wt % in the lower layer.
[0084] Table 2 shows the results for Examples 8 to 14 and Comparative Example 2, in which the weight fraction of SiO contained in the second negative electrode active material layer is relatively small.
[0085]
[0086] This table also shows the weight fractions of SiO, CNT, and binder, which are examples of Si-based particles, the compressive load required to make the density of graphite, which corresponds to the hardness of the graphite particles, 1.7 g / cc, the weight fraction of added acetylene black, and the percentage of the charge rate ratio (3 C charge rate) / (0.2 C charge rate).
[0087] Specifically, the weight fraction of SiO is 5 to 15 wt% in the upper layer and 25 to 35 wt% in the lower layer. The weight fraction of CNT is 0.03 to 0.10 wt% in the upper layer and 0.10 to 0.17 wt% in the lower layer. The weight fraction of binder is 2 to 5 wt% in the upper layer and 5 to 8 wt% in the lower layer. The compressive load of graphite is 2.5 to 3.5 kN / cm in the upper layer. ２ , 1.5 to 2.5 kN / cm in the lower layer ２ The weight fraction of acetylene black is 0.5 to 2.0 wt % in the upper layer and 2.0 to 3.5 wt % in the lower layer.
[0088] Other Embodiments The configurations of the negative electrode and lithium ion secondary battery of the present disclosure are not limited to the configurations of the lithium ion secondary battery described in the embodiments, and can be applied to batteries having various shapes and configurations.
[0089] The embodiments have been described in detail or simply to make the present disclosure easier to understand, and do not necessarily include all of the components described, or may include components not shown. Furthermore, some of the components of the embodiments may be deleted, replaced with components of other embodiments, or combined with components of other embodiments.
[0090] The lithium ion secondary battery of the present disclosure can be applied to drive motors for electric vehicles, power sources for portable electronic devices such as smartphones, charging devices for stationary power generation devices, and the like.
[0091] The negative electrode is not limited to a configuration in which a negative electrode tab protrudes from the negative electrode current collector. For example, the negative electrode may be configured such that an end of the wound negative electrode current collector is electrically connected to a negative electrode terminal via a negative electrode current collector plate. Alternatively, the negative electrode may be configured such that an end of the wound negative electrode current collector is electrically connected to a negative electrode terminal.
[0092] The charge / discharge body is not limited to a wound type in which a long positive electrode and a long negative electrode are wound with a long separator interposed therebetween as shown in FIG. 2 . For example, the charge / discharge body may be a laminated type in which a plurality of rectangular positive electrodes, separators, and negative electrodes are stacked. The charge / discharge body may also be a laminated type in which a plurality of relatively short positive electrodes and a plurality of negative electrodes are alternately arranged facing each other with the separator interposed therebetween, with the separator folded and stacked. In a charge / discharge body of this configuration, the separator is folded and stacked, so that the positive electrode and the negative electrode face each other with the separator interposed therebetween.
[0093] The lithium ion secondary battery of the present disclosure is not limited to a configuration in which the charging / discharging body is sealed with a case and a lid. For example, the lithium ion secondary battery may be configured such that the charging / discharging body is sealed with a laminate film.
[0094] The separator that insulates the positive electrode from the negative electrode may be formed of an insulating member laminated on the electrode. The insulating member is bonded to the positive electrode or the negative electrode. The insulating member preferably has heat resistance. In this case, the insulating member is made of, for example, ceramics. This configuration corresponds to a so-called separatorless configuration. A configuration using an insulating member in addition to a separator, i.e., a configuration using both a separator and an insulating member, may also be used.
[0095] The effects of the lithium ion secondary battery of the present disclosure will be described below.
[0096] Silicon oxide-based active materials used in the negative electrodes of lithium-ion secondary batteries may expand and contract during charge and discharge, which may cause microcracks to form in the negative electrode active material layer. These microcracks may facilitate the penetration of electrolyte. In this case, mixing carbon nanotubes as a component of the negative electrode active material layer may suppress the expansion and contraction of the negative electrode active material layer. Suppressing the expansion and contraction of the negative electrode active material layer suppresses the generation of microcracks, thereby suppressing the penetration of electrolyte. Suppressing the generation of microcracks in this way may result in a deterioration of charge and discharge characteristics.
[0097] According to the present disclosure, in the negative electrode used in the lithium ion secondary battery, Si or SiO ｘ This can prevent the occurrence of microcracks in the negative electrode active material layer due to the expansion and contraction of particles containing (0<x<2), etc., thereby improving the charge-discharge characteristics of the lithium ion secondary battery.
[0098] 1: Lithium ion secondary battery, 100: Charge / discharge body, 110: Positive electrode, 111: Positive electrode current collecting layer, 111b: Positive electrode tab, 112: First positive electrode active material layer, 112a, 112b, 113a: Positive electrode active material, 112d, 113c: Positive electrode binder, 113: Second positive electrode active material layer, 120: Negative electrode, 121: Negative electrode current collecting layer, 121b: Negative electrode tab, 122, 124: First negative electrode active material layer, 12 2a, 123a, 124a, 125a: graphite particles, 122b, 123b, 124b, 125b: Si-based particles, 122c, 123c, 124c, 125c: carbon nanotubes, 122d, 123d, 124d, 125d: binder, 123: second negative electrode active material layer, 130: separator, 201: case, 202: lid, 301: positive electrode terminal, 302: negative electrode terminal.
Claims
1. A lithium-ion secondary battery comprising a positive electrode and a negative electrode, wherein the negative electrode comprises a negative electrode current collector and a negative electrode active material layer laminated on the negative electrode current collector, wherein the negative electrode active material layer comprises a first negative electrode active material layer laminated on the negative electrode current collector and a second negative electrode active material layer laminated on the first negative electrode active material layer, wherein the first negative electrode active material layer and the second negative electrode active material layer contain Si-based particles, wherein the weight fraction of the Si-based particles in the second negative electrode active material layer is greater than the weight fraction of the Si-based particles in the first negative electrode active material layer, and wherein the negative electrode active material layer has at least one of the following configurations (1) to (4): Configuration (1): The first negative electrode active material layer and the second negative electrode active material layer contain carbon nanotubes, and the weight fraction of the carbon nanotubes in the second negative electrode active material layer is greater than the weight fraction of the carbon nanotubes in the first negative electrode active material layer. Configuration (2): The first negative electrode active material layer and the second negative electrode active material layer contain a binder, and the weight fraction of the binder in the second negative electrode active material layer is greater than the weight fraction of the binder in the first negative electrode active material layer. Configuration (3): The first negative electrode active material layer and the second negative electrode active material layer contain amorphous carbon, and the weight fraction of the amorphous carbon in the second negative electrode active material layer is greater than the weight fraction of the amorphous carbon in the first negative electrode active material layer. Configuration (4): The first negative electrode active material layer and the second negative electrode active material layer contain graphite as a main component, and the hardness of the graphite in the first negative electrode active material layer is greater than the hardness of the graphite in the second negative electrode active material layer.
2. The Si-based particles are Si or SiO ｘ The lithium ion secondary battery of claim 1 , wherein x is a number in the range of 0<x<2.
3. A lithium-ion secondary battery comprising: a negative electrode current collector; and a negative electrode active material layer laminated on the negative electrode current collector, wherein the negative electrode active material layer includes a first negative electrode active material layer laminated on the negative electrode current collector and a second negative electrode active material layer laminated on the first negative electrode active material layer, wherein the first negative electrode active material layer and the second negative electrode active material layer contain Si-based particles, wherein the weight fraction of the Si-based particles in the second negative electrode active material layer is smaller than the weight fraction of the Si-based particles in the first negative electrode active material layer, and wherein the negative electrode active material layer has at least one of the following configurations (5) to (8): Configuration (5): The first negative electrode active material layer and the second negative electrode active material layer contain carbon nanotubes, and the weight fraction of the carbon nanotubes in the second negative electrode active material layer is smaller than the weight fraction of the carbon nanotubes in the first negative electrode active material layer. Configuration (6): The first negative electrode active material layer and the second negative electrode active material layer contain a binder, and the weight fraction of the binder in the second negative electrode active material layer is smaller than the weight fraction of the binder in the first negative electrode active material layer. Configuration (7): The first negative electrode active material layer and the second negative electrode active material layer contain amorphous carbon, and the weight fraction of the amorphous carbon in the second negative electrode active material layer is smaller than the weight fraction of the amorphous carbon in the first negative electrode active material layer. Configuration (8): The first negative electrode active material layer and the second negative electrode active material layer contain graphite as a main component, and the hardness of the graphite in the second negative electrode active material layer is harder than the hardness of the graphite in the first negative electrode active material layer.
4. The Si-based particles are Si or SiO ｘ The lithium ion secondary battery according to claim 3 , wherein x is a number in the range of 0<x<2.