WO2011114709A1

WO2011114709A1 - Lithium secondary battery

Info

Publication number: WO2011114709A1
Application number: PCT/JP2011/001502
Authority: WO
Inventors: 秀治武澤; 朝樹塩崎; 泰右山本
Original assignee: パナソニック株式会社
Priority date: 2010-03-18
Filing date: 2011-03-15
Publication date: 2011-09-22

Abstract

A lithium secondary battery (100) comprising a positive electrode (30), a negative electrode (20), a separator (13) arranged between the positive electrode (30) and the negative electrode (20), and an electrolytic solution having lithium ion conductivity, wherein the negative electrode (20) comprises a negative electrode current collector (21) having multiple convex parts (22) on the surface thereof and a negative electrode active material layer (23) formed on the negative electrode current collector (21) and containing multiple active material bodies (24), wherein the multiple active material bodies (24) are respectively placed on the convex parts (22) in the negative electrode current collector (21) and contain an alloy active material containing silicon or tin as a negative electrode active material, and wherein a porous insulating layer (15) mainly composed of an inorganic oxide is provided between the positive electrode (30) and the negative electrode (20).

Description

Lithium secondary battery

The present invention relates to a lithium secondary battery, particularly a lithium secondary battery containing an alloy-based active material.

Lithium secondary batteries have high capacity and high energy density, and can be easily reduced in size and weight. For example, mobile phones, personal digital assistants (PDAs), notebook personal computers, video cameras, portable game machines, etc. It is widely used as a power source for portable electronic devices. In recent years, in portable small electronic devices, further multi-functionalization has been promoted, and continuous use time has been required to be extended. In addition, lithium secondary batteries are expected not only as a power source for small electronic devices but also as a power source for large devices such as hybrid cars, electric vehicles, and electric tools. In order to meet these demands, it is necessary to further increase the capacity of lithium secondary batteries used as power sources.

Generally, a lithium secondary battery includes a substrate (current collector), a negative electrode including a negative electrode active material layer (negative electrode active material layer) formed on the substrate, a substrate (current collector), The positive electrode comprised from the layer (positive electrode active material layer) containing the positive electrode active material formed on the board | substrate, and the separator arrange | positioned between a positive electrode and a negative electrode are provided.

In order to further increase the capacity of the lithium secondary battery, for example, development of a negative electrode using a high-capacity negative electrode active material is underway. For example, Patent Document 1 discloses the use of silicon, tin, oxides thereof, nitrides thereof, compounds containing them, alloys, and the like as a high-capacity negative electrode active material. In addition, in order to suppress an increase in the amount of heat generated due to an increase in energy density, it is proposed to provide a separator including a porous heat-resistant layer.

However, when an alloy containing silicon or tin is used as the negative electrode active material, there are the following problems. The alloy-based active material has a large volume expansion / contraction due to insertion / extraction of lithium ions. For this reason, if charging / discharging is repeated, there is a possibility that current collection failure may occur between the substrate and the negative electrode active material layer, or the negative electrode may be flawed or broken. These are factors that deteriorate the charge / discharge cycle characteristics of the lithium secondary battery.

On the other hand, a structure (columnar structure) in which a columnar active material body is arranged on each convex portion using a substrate having a plurality of convex portions as a negative electrode structure that suppresses deterioration of charge / discharge cycle characteristics has been proposed. (See Patent Documents 2 and 3).

Patent Document 2 proposes that a negative electrode active material film is formed by directly depositing a negative electrode active material on a substrate having an uneven surface by a vapor phase method such as sputtering. The negative electrode active material film is separated into a plurality of columnar active material bodies by charging and discharging while maintaining the current collecting property with the substrate. As a result, a space is self-formed between the active material members. Since this space can relieve stress due to expansion / contraction, the charge / discharge cycle characteristics can be improved. Patent Document 3 proposes using a substrate having a plurality of convex portions and forming a negative electrode active material only on the convex portions. In Patent Document 3, a plurality of resist patterns are formed on a substrate, and copper and a negative electrode active material are deposited thereon. Next, the resist pattern and the copper and negative electrode active material thereon are removed by lift-off. Thereby, while forming the convex part which consists of copper on a board | substrate, a negative electrode active material can be formed only on a convex part. According to Patent Document 3, since a space is previously formed between the negative electrode active materials, the expansion stress is effectively maintained while maintaining the current collecting ability more effectively than when the space is formed by charging and discharging (the negative electrode of Patent Document 2). Can be relaxed.

International Publication No. 2006/134684 JP 2002-83594 A JP 2007-12421 A

As a result of studies by the present inventor, when a high-capacity negative electrode active material such as silicon is used, in addition to the deterioration of the negative electrode itself, the deterioration of the positive electrode is larger than when a conventional negative electrode active material (for example, carbon) is used. I found out. This deterioration of the positive electrode is particularly remarkable when the negative electrode has a columnar structure as proposed in Patent Documents 2 and 3. This is presumably because the positive electrode active material layer is stressed due to the volume change of the negative electrode active material layer due to repeated charge and discharge, and the positive electrode active material falls off, thereby reducing the positive electrode capacity. The reason why the deterioration of the positive electrode becomes large will be described in detail later.

Therefore, according to the structures proposed in Patent Documents 2 and 3, although the deterioration of the negative electrode due to the volume change of the negative electrode active material can be suppressed, the deterioration of the positive electrode becomes larger than the conventional one. Characteristics may not be obtained.

The present invention has been made in view of the above circumstances, and an object thereof is to suppress deterioration of the negative electrode and the positive electrode due to repeated charge and discharge in a lithium secondary battery using an alloy containing silicon or tin as a negative electrode active material. Thus, the charge / discharge cycle characteristics are improved.

The lithium secondary battery of the present invention includes a positive electrode having a positive electrode active material capable of occluding and releasing lithium ions, a negative electrode having a negative electrode active material capable of occluding and releasing lithium ions, and a gap between the positive electrode and the negative electrode. A lithium secondary battery comprising a separator disposed and an electrolyte having lithium ion conductivity, wherein the negative electrode has a negative electrode current collector having a plurality of protrusions on the surface, and the negative electrode current collector. A negative electrode active material layer including a plurality of active material bodies formed, and each of the plurality of active material bodies is disposed on each convex portion of the negative electrode current collector, and silicon or An alloy-based active material containing tin is included, and a porous insulating layer mainly composed of an inorganic oxide is further provided between the positive electrode and the negative electrode.

Since the lithium secondary battery of the present invention uses an alloy-based active material containing silicon or tin as a negative electrode active material, the energy density is high. In the negative electrode, since the plurality of active material bodies including the negative electrode active material are disposed on the respective convex portions on the surface of the current collector, the stress accompanying expansion and contraction of the negative electrode active material can be relaxed. Furthermore, since a porous insulating layer mainly composed of an inorganic oxide is provided between the positive electrode and the negative electrode, the stress generated in the positive electrode active material layer due to the volume change of the negative electrode can be reduced, and the positive electrode active material can be prevented from falling off. Can do. Therefore, it is possible to suppress a decrease in the positive electrode capacity due to the falling off of the positive electrode active material.

Thus, according to the present invention, not only the deterioration of the negative electrode but also the deterioration of the positive electrode caused by the volume change of the negative electrode active material can be suppressed, so that the charge / discharge cycle characteristics can be improved.

It is sectional drawing which shows typically the electrode group in the lithium secondary battery 100 of embodiment by this invention. (A) And (b) is typical sectional drawing for demonstrating the stress concerning a positive electrode in the conventional lithium secondary battery using the negative electrode which has a columnar structure, (a) is before charging. (During discharging), (b) shows the state during charging. (A) And (b) is typical sectional drawing for demonstrating the stress concerning a positive electrode in the lithium secondary battery using the negative electrode of 1st Embodiment by this invention, (a) is charge. Before performing (when discharging), (b) shows the state during charging. (A) And (b) is typical sectional drawing for demonstrating the stress concerning a positive electrode in the conventional lithium secondary battery using the negative electrode which does not have a columnar structure, (a) performs charge. The previous (during discharging) and (b) show the state during charging, respectively. (A)-(c) is typical sectional drawing for demonstrating the mechanism in which electrolyte solution reduces by charging / discharging in the conventional lithium secondary battery provided with the negative electrode which has a columnar structure, respectively. (A)-(c) is typical sectional drawing for demonstrating the effect acquired by arrange | positioning the porous insulating layer 15 in the lithium secondary battery 100 of embodiment by this invention, respectively. It is sectional drawing which shows an example of the lithium secondary battery 200 of 1st Embodiment by this invention. 3 is an enlarged cross-sectional view schematically showing an active material body included in a negative electrode active material layer in a lithium secondary battery 200. FIG. 3 is a perspective view schematically showing an example of a negative electrode current collector in a lithium secondary battery 200. FIG. 4 is an enlarged cross-sectional view schematically showing an active material body included in another negative electrode active material layer in the lithium secondary battery 200. FIG. 2 is a cross-sectional view schematically showing a configuration of an electron beam evaporation apparatus 50. FIG. It is sectional drawing which shows the other lithium secondary battery of 1st Embodiment by this invention. FIG. 3 is a schematic cross-sectional view showing a configuration of an electrode group (a porous insulating layer is formed on the surface of a positive electrode) in the lithium secondary batteries of Examples 1 to 4, 6, and 7. 6 is a schematic cross-sectional view showing a configuration of an electrode group (a porous insulating layer is formed on a separator surface) in a lithium secondary battery of Example 5. FIG. FIG. 4 is a schematic cross-sectional view showing a configuration of an electrode group (having no porous insulating layer) in lithium secondary batteries of Comparative Examples 1 to 3. (A) And (b) is a figure for demonstrating the charging / discharging cycling characteristics of the conventional lithium secondary battery.

The present inventor repeated diligent studies to further improve the charge / discharge cycle characteristics in a conventional lithium secondary battery including a negative electrode having a columnar structure. As a result, it was found that not only the negative electrode but also the positive electrode deteriorated by repeated charge and discharge. In particular, it has also been found that the positive electrode may be greatly deteriorated as compared with the case where a negative electrode having no columnar structure is used.

16 (a) and 16 (b) are diagrams illustrating results of measuring charge / discharge cycle characteristics of a conventional lithium secondary battery. In FIG. 16A, a graph 71 shows charge / discharge cycle characteristics of a lithium secondary battery (referred to as “battery II”) using carbon (C) as a negative electrode active material, and a graph 72 shows a negative electrode active material. The charge / discharge cycle characteristics of a lithium secondary battery (referred to as “battery I”) using silicon oxide (SiOx) are shown. As the positive electrode active material, a nickel acid positive electrode material is used. In FIG. 16B, graph 73 and graph 75 show the charge / discharge cycle characteristics of the negative electrode and the positive electrode (changes in negative electrode capacity and positive electrode capacity accompanying the charge / discharge cycle), respectively, in the battery II. Similarly, graph 74 and graph 76 show the charge / discharge cycle characteristics of the negative electrode and the positive electrode in Battery I, respectively.

As can be seen from FIGS. 16 (a) and 16 (b), the battery I using silicon oxide having a large volume change associated with insertion and extraction of lithium as the negative electrode active material is more effective than the battery II using carbon. The charge / discharge cycle characteristics of the graph are degraded (graphs 71 and 72). In addition, in Battery I, it can be seen that the positive electrode is deteriorated in addition to the negative electrode as the charge / discharge cycle is repeated (graphs 74 and 76). The deterioration of the negative electrode of the battery I is larger than the deterioration of the negative electrode of the battery II. This is considered because the negative electrode of the battery I is more easily deteriorated due to the volume change of the silicon oxide. Moreover, it turns out that the deterioration of the positive electrode of the battery I is larger than the deterioration of the positive electrode of the battery II.

Thus, in the battery I using silicon oxide, not only the deterioration of the negative electrode but also the deterioration of the positive electrode is larger than in the battery II using carbon. For this reason, it is considered that not only the negative electrode capacity but also the positive electrode capacity is reduced with the charge / discharge cycle characteristics, and as a result, the battery capacity is reduced.

As a result of examination by the present inventors, the cause of the deterioration of the positive electrode of the battery I is considered as follows. When a high-capacity negative electrode active material such as silicon oxide is used, the negative electrode active material greatly expands and contracts with charge and discharge. In particular, when the negative electrode has a columnar structure, the volume change of each active material body is further increased. This volume change of the active object gives local stress to the positive electrode active material layer, and as a result, the positive electrode active material layer is likely to fall off partially. In addition, the positive electrode active material is generally composed of a material having a lower strength than the negative electrode active material, and is easily dropped or deformed. When the positive electrode active material layer falls off, the positive electrode capacity decreases, which causes a decrease in battery capacity.

In addition, when the negative electrode does not have a columnar structure, the deterioration of the negative electrode capacity (decrease in the negative electrode capacity) is large, so the decrease in charge / discharge cycle characteristics of the battery is mainly due to the decrease in the negative electrode capacity. Is hardly a problem. On the other hand, when the negative electrode has a columnar structure, the deterioration of the negative electrode is suppressed to some extent, and the positive electrode capacity is greatly reduced as the volume change of the negative electrode increases. For this reason, the deterioration of the positive electrode becomes obvious, and the possibility of becoming one of the main factors that deteriorate the charge / discharge cycle characteristics of the battery increases. Therefore, in order to improve the charge / discharge cycle characteristics of the battery, it is more important to suppress the decrease in the positive electrode capacity.

Based on the above findings, the present inventor has repeatedly studied a battery structure that suppresses deterioration of the positive electrode. As a result, it has been found that by providing a porous insulating layer mainly composed of an inorganic oxide between the positive electrode and the negative electrode, the stress applied to the positive electrode active material layer due to the volume change of the negative electrode can be reduced. It came.

Hereinafter, embodiments of the lithium secondary battery according to the present invention will be described more specifically with reference to the drawings.

(First embodiment)
A first embodiment of a lithium secondary battery according to the present invention will be described. FIG. 1 is a schematic cross-sectional view of a lithium secondary battery 100 of the present embodiment.

The lithium secondary battery 100 of this embodiment includes a negative electrode 20, a positive electrode 30, a separator 13 disposed between the negative electrode 20 and the positive electrode 30, a porous insulating layer 15, and an electrolytic solution having lithium ion conductivity. (Not shown). The negative electrode 20 includes a negative electrode current collector 21 having a plurality of protrusions 22 on the surface, and a negative electrode active material layer 23 formed on the surface of the negative electrode current collector 21. The positive electrode 30 includes a positive electrode current collector 31 and a positive electrode active material layer 33 formed on the surface of the positive electrode current collector 31. The positive electrode 30 and the negative electrode 20 are disposed so that the negative electrode active material layer 23 and the positive electrode active material layer 33 are opposed to each other with the separator 13 interposed therebetween.

The porous insulating layer 15 is provided between the positive electrode active material layer 33 and the negative electrode active material layer 23. The porous insulating layer 15 contains an inorganic oxide as a main component, and has lithium ion permeability and insulating properties during normal use of a lithium secondary battery.

The negative electrode active material layer 23 has a plurality of columnar active material bodies 24 arranged on the convex portions 22 of the negative electrode current collector 21. The active material body 24 includes an alloy-based active material containing silicon or tin as a negative electrode active material. It is preferable that the active material bodies 24 are arranged at intervals (spaces 26) from each other during discharge. In addition, when each active material body 24 expand | swells by charge, the space 26 between the active material bodies 24 will become small. As a result, the adjacent active material bodies 24 may come into contact with each other, or the space 26 may be almost lost, and the negative electrode active material layer 23 may become a continuous film.

<Effects of porous insulating layer 15>
-Stress buffering effect of porous insulating layer 15 The porous insulating layer 15 in this embodiment is sufficiently hard because it is mainly composed of an inorganic oxide, and reduces the stress applied to the positive electrode active material layer 33 by the volume change of the negative electrode active material. Functions as a buffer layer. Therefore, according to this embodiment, it is possible to suppress the deterioration of the positive electrode due to the volume change of the negative electrode.

Hereinafter, the effects of disposing the porous insulating layer 15 will be described in more detail with reference to FIGS.

FIG. 2 is a schematic cross-sectional view for explaining the stress applied to the positive electrode in a conventional lithium secondary battery using a negative electrode having a columnar structure. FIG. 3 is a schematic cross-sectional view for explaining the stress applied to the positive electrode in the lithium secondary battery of this embodiment. (A) in each figure shows a state before charging (during discharging), and (b) in each figure shows a state during charging. For simplicity, the same components as those in FIG.

As can be seen from FIGS. 2A and 2B, in the conventional lithium secondary battery having a columnar structure, when charging is started, each active material body 24 absorbs lithium and expands, and adjacent active material bodies. 24 come into contact with each other. Each active material body 24 also expands in the thickness direction and applies mechanical stress to the separator 13. Such expansion stress of the active material body 24 is transmitted to the positive electrode active material layer 33 through the separator 13. As a result, the portion 33p located above the active material body 24 in the positive electrode active material layer 33 is pressed, and stress (mechanical stress) s1 is generated. As described above, since the large stress s1 is partially applied to the positive electrode active material layer 33, the positive electrode active material is likely to fall off.

In contrast, in the present embodiment, as shown in FIGS. 3A and 3B, the porous insulating layer 15 is disposed between the positive electrode 30 and the separator 13. When each active material body 24 expands during charging, the expansion stress is transmitted to the porous insulating layer 15 via the separator 13. Since the porous insulating layer 15 is mainly composed of an inorganic oxide and is sufficiently hard, the expansion stress from the negative electrode 20 side is dispersed by the porous insulating layer 15. As a result, the stress s2 transmitted to the positive electrode active material layer 33 is smaller than the stress s1 transmitted to the positive electrode active material layer 33 in the conventional lithium secondary battery. Accordingly, it is possible to suppress the loss of the positive electrode active material due to the volume change of the negative electrode 20 as compared with the conventional case, and it is possible to suppress the decrease in the positive electrode capacity due to the drop of the positive electrode active material.

As described above, according to the present embodiment, by providing the porous insulating layer 15, the stress applied to the positive electrode active material layer 33 due to the volume change of the negative electrode active material can be reduced. Therefore, since the deterioration of the positive electrode 30 due to repeated charge / discharge can be suppressed as compared with the conventional case, the charge / discharge cycle characteristics can be improved.

For reference, FIGS. 4A and 4B are schematic cross-sectional views for explaining the stress applied to the positive electrode in a conventional lithium secondary battery using a negative electrode having no columnar structure. Show.

As can be seen from FIGS. 4A and 4B, in a conventional lithium secondary battery having no columnar structure (for example, Patent Document 1), the negative electrode active formed on the negative electrode 121 is started when charging is started. The material layer 123 absorbs lithium and expands in the thickness direction. When a negative electrode active material containing silicon or tin is used, the negative electrode active material layer 123 expands greatly, and the mechanical stress is applied to the positive electrode active material layer 33. This mechanical stress (stress) is substantially uniformly applied to the entire surface of the positive electrode active material layer 33, unlike the stresses s1 and s2 shown in FIGS. Since the positive electrode active material layer 33 is not partially pressed (unevenly pressed), it is considered that the positive electrode active material does not easily fall off. Further, if the columnar structure is not provided, the negative electrode 20 itself is largely deteriorated due to the expansion of the negative electrode active material, so that the problem of deterioration of the positive electrode 30 does not become obvious. On the other hand, when a carbon-based material is used as the negative electrode active material, the negative electrode active material layer 123 has a small expansion coefficient, so that the problem of deterioration of the negative electrode 20 and the positive electrode 30 due to the expansion stress of the negative electrode active material does not occur. From this, the deterioration of the positive electrode 30 due to the volume change of the negative electrode active material is a problem peculiar to the lithium secondary battery including the negative electrode 20 including the negative electrode active material containing silicon or tin and having the columnar structure. I understand.

The porous insulating layer 15 is preferably harder than the separator 13. Thereby, the function as a buffer layer can be exhibited more effectively.

In the present embodiment, the porous insulating layer 15 is disposed between the positive electrode active material layer 33 and the separator 13, but the position of the porous insulating layer 15 is not limited to the illustrated position. If the porous insulating layer 15 is disposed between the positive electrode active material layer 33 and the negative electrode active material layer 23, the above effect can be obtained. In addition, the porous insulating layer 15 may be formed on at least a part of a portion located between the positive electrode active material layer 33 and the negative electrode active material layer 23 in a plane parallel to the negative electrode current collector 21. . However, it is preferable to be formed over the entire portion because dropping of the positive electrode active material from the positive electrode active material layer 33 can be more effectively suppressed.

The thickness of the porous insulating layer 15 is preferably 1 μm or more. If thickness is 1 micrometer or more, since the stress from a negative electrode side can be relieve | moderated more reliably, charging / discharging cycle life can be improved more effectively. On the other hand, the thickness of the porous insulating layer 15 is preferably 10 μm or less. When the thickness exceeds 10 μm, the total thickness of the separator 13 and the porous insulating layer 15 increases, and thus the capacity may be reduced. In this case, in order to maintain a high capacity, the separator 13 can be made thinner by the thickness of the porous insulating layer 15 to suppress an increase in the total thickness of the separator 13 and the porous insulating layer 15. However, if the porous insulating layer 15 is thick (for example, more than 10 μm), the thickness of the separator 13 cannot be sufficiently secured, and there is a possibility that the insulating property cannot be maintained.

The negative electrode active material layer 23 should just be comprised from the active material body 24 formed on each convex part 22 of the electrical power collector 21. FIG. However, as shown in the figure, it is preferable that a space is formed between the adjacent active material bodies 24 during discharge. Thereby, since the space which each active material body 24 expand | swells by occlusion of lithium can be ensured, the peeling of the negative electrode active material and the deformation | transformation of the negative electrode 20 by the expansion stress of the active material body 24 can be suppressed at the time of charge. Further, since the expansion in the thickness direction can be reduced by the amount that each active material body 24 expands in the lateral direction during charging, the stress applied to the positive electrode active material layer 33 can be reduced.

The buffering effect of stress by disposing the porous insulating layer 15 becomes more prominent as the volume change due to charging / discharging of the active material body 24 becomes larger. In the present specification, the volume change of the active material body 24 means (volume of active material body during charging−volume of active material body during discharge) / volume (%) of active material body during discharge. The volume change of the active material body 24 is preferably 200% or more, for example. Thereby, since the deterioration of the positive electrode 30 caused by the volume change can be suppressed while securing a high capacity, the charge / discharge cycle characteristics can be improved more effectively.

Although the porous insulating layer 15 is inferior to the separator (resin separator) 13, it has a high insulating property and an excellent ion permeability, and thus has a function as a separator. Therefore, even if the porous insulating layer 15 is disposed between the positive electrode 30 and the negative electrode 20, the movement of the electrolytic solution is not hindered, so that the effects as described above can be obtained while maintaining the battery performance. .

Antioxidation effect of the separator 13 by the porous insulating layer 15 When the porous insulating layer 15 is disposed on the positive electrode side of the separator (resin separator) 13, the inorganic oxide has high chemical stability. It is possible to prevent the surface of the positive electrode side from being oxidized. Accordingly, it is possible to suppress an increase in resistance due to the surface alteration of the separator 13.

Electrolytic solution retention effect of porous insulating layer 15 The surface of the porous insulating layer 15 has higher wettability with respect to the electrolytic solution than the surface of the positive electrode 30 (here, the surface of the positive electrode active material layer 33). Preferably it is. Thereby, it has the function to hold | maintain and osmose | permeate electrolyte solution. Therefore, the capacity | capacitance fall accompanying the reduction | decrease of the electrolyte solution on the positive electrode side can be suppressed.

Hereinafter, the reason why the porous insulating layer 15 can suppress the decrease in the electrolyte along with the problems in the conventional lithium secondary battery will be described in detail with reference to the drawings.

The present inventor has found that the conventional lithium secondary battery has a problem that the electrolyte solution on the positive electrode side gradually decreases due to repeated charge and discharge, resulting in a decrease in capacity and a decrease in charge / discharge cycle characteristics. It was. This is presumably because a phenomenon occurs in which the electrolyte solution on the positive electrode side gradually decreases when charging and discharging are repeated. This phenomenon is particularly noticeable in a lithium secondary battery using a negative electrode having a columnar structure, and is considered to be one of the factors that make it difficult to further improve the charge / discharge cycle characteristics.

Hereinafter, the reason why the electrolyte solution on the positive electrode side decreases with repeated charge and discharge in the conventional lithium secondary battery will be described with reference to the drawings.

FIG. 5A is a cross-sectional view showing a state of the lithium secondary battery before charging. The lithium secondary battery includes a negative electrode 20, a separator 13, and a positive electrode 30 disposed to face the negative electrode 20 with the separator 13 interposed therebetween. The negative electrode 20 includes a current collector 21 and a negative electrode active material layer 23 formed on the surface of the current collector 21. The negative electrode active material layer 23 is composed of a plurality of columnar active material bodies (active material bodies) 24. In addition, an electrolyte solution (not shown) exists between the positive electrode 30 and the negative electrode 20.

As shown in FIG. 5A, in the state before charging, the plurality of active material bodies 24 are arranged at intervals. For this reason, the electrolytic solution enters the space 26 between the active material bodies 24.

Thereafter, when charging is started, as shown in FIG. 5B, each active material member 24 expands by absorbing lithium, and adjacent active material members 24 come into contact with each other. As a result, there is almost no space between the active material bodies 24, and the negative electrode active material layer 23 becomes a continuous film. Since each active material body 24 expands not only in the width direction of the active material body 24 but also in the height direction, the thickness of the negative electrode active material layer 23 also increases. For this reason, a part of the electrolytic solution that has entered the space 26 of the active material body 24 is discharged out of the system (arrow 45).

In this specification, a region sandwiched between the positive electrode active material layer 33 and the negative electrode active material layer 23 is referred to as “inside system”, and a region other than the above region in the lithium secondary battery is referred to as “outside system”.

Thereafter, when the discharge is started again, as shown in FIG. 5C, each active material body 24 contracts, and a space 26 is formed between the adjacent active material bodies 24. At this time, the amount of the electrolyte solution on the negative electrode side is smaller than that during the previous discharge (FIG. 5A). This is because the electrolyte discharged outside the system at the time of charging is difficult to return to the system even after discharging. Moreover, since the electrolyte solution on the negative electrode side is consumed by the side reaction of the negative electrode 20, it further decreases.

In addition, when a “crack” occurs in the negative electrode active material layer due to expansion / contraction of the negative electrode active material, a new surface is exposed at the cracked portion. The above-mentioned “side reaction” includes a reaction in which the electrolytic solution undergoes reductive decomposition on a new surface exposed by cracking. In addition, the negative electrode active material itself and the electrolytic solution directly react with each other to include a reaction in which the negative electrode active material is altered (oxidation or the like).

When the space 26 is formed in a state where the amount of the electrolyte solution on the negative electrode side is reduced, a part of the electrolyte solution on the positive electrode side moves to the negative electrode side via the separator 13 as indicated by an arrow 47. This is presumably because the wettability of the surface of the negative electrode 20 (namely, the surface of the negative electrode active material layer 23) is higher than the wettability of the surface of the positive electrode 30 (the surface of the positive electrode active material layer).

Thereafter, when charging and discharging are further repeated, the amount of the electrolytic solution in the system, particularly the electrolytic solution on the positive electrode side, gradually decreases. When the electrolyte solution on the positive electrode side decreases, the reaction occurs non-uniformly in the positive electrode 30 and the deterioration proceeds.

Thus, as charging / discharging is repeated, the negative electrode 20 deteriorates, and the deterioration of the positive electrode is accelerated by the deterioration of the negative electrode 20. For this reason, it is difficult to further improve the charge / discharge cycle characteristics.

On the other hand, in this embodiment, since the porous insulating layer 15 having high wettability is disposed between the positive electrode 30 and the negative electrode 20, the electrolytic solution is difficult to move from the positive electrode 30 to the negative electrode 20, and as a result, the positive electrode The decrease of the electrolyte solution on the side can be suppressed.

6A to 6C are schematic cross-sectional views showing a lithium secondary battery according to an embodiment of the present invention. FIG. 6A shows a state before charging (during discharging), and FIG. FIG. 6 (c) shows a state where the battery is discharged again after being charged as shown in FIG. 6 (b). In FIG. 6, convex portions on the surface of the negative electrode current collector 21 are omitted.

As shown in FIG. 6A, in the state before charging, in the negative electrode 20, the space 26 between the active material bodies 24 is electrolyzed in the same manner as the conventional lithium secondary battery shown in FIG. Liquid has entered.

Thereafter, when charging is started, as shown in FIG. 6B, each active material member 24 absorbs lithium and expands. As a result, in the negative electrode active material layer 23, adjacent active material bodies 24 are in contact with each other. Moreover, the thickness of the negative electrode active material layer 23 also increases. When the thickness of the negative electrode active material layer 23 before charging is t, the thickness of the negative electrode active material layer 23 is t + Δt by charging. At this time, a part of the electrolytic solution that has entered the space 26 of the active material body 24 flows out of the system as indicated by an arrow 41. For this reason, the electrolyte solution on the negative electrode side decreases by the amount that flows out of the system.

Thereafter, as shown in FIG. 6C, the next discharge is started in a state where the electrolyte solution on the negative electrode side is insufficient, and a space 26 is formed again between the active material bodies 24. In the present embodiment, the porous insulating layer 15 having a surface with higher wettability than the surface of the positive electrode 30 is disposed between the positive electrode 30 and the negative electrode 20. For this reason, even if the space 26 is formed in a state where the electrolyte solution on the negative electrode side is reduced, the electrolyte solution on the positive electrode side is held by the porous insulating layer 15 and hardly moves to the negative electrode side. Accordingly, it is possible to suppress the decrease in the electrolyte solution on the positive electrode side as compared with the conventional lithium secondary battery (FIG. 5B). In this embodiment, since the movement of the electrolytic solution from the positive electrode side is suppressed, a part of the electrolytic solution flowing out of the system is returned to the space 26 of the active material body 24 as indicated by an arrow 43. It becomes easy.

As described above, according to the present embodiment, by providing the porous insulating layer 15, it is possible to suppress the movement of the electrolyte solution from the positive electrode side to the negative electrode side, thereby suppressing the decrease in the electrolyte solution on the positive electrode side due to charge / discharge. Can do. Therefore, the deterioration of the positive electrode due to repeated charge / discharge can be suppressed more than before. In addition, since a part of the electrolytic solution that flows out of the system during charging is easily returned to the system, a decrease in the amount of the electrolytic solution in the system is also suppressed. Therefore, the charge / discharge cycle characteristics can be further improved as compared with the prior art.

The porous insulating layer 15 preferably has a higher porosity (porosity) than the separator 13. Assuming that the thickness T ′ of the separator 13 in the conventional lithium secondary battery shown in FIG. 5 is equal to the total thickness T of the separator 13 and the porous insulating layer 15 in the present embodiment, the porous insulating layer 15 is empty. By making the porosity higher than the porosity of the separator 13, it is possible to reduce the amount of the electrolyte flowing out of the system during charging. Therefore, it is possible to more effectively suppress the decrease in the electrolyte solution in the system.

Further, the ratio of the thickness of the porous insulating layer 15 to the thickness of the separator 13 is preferably 5% or more, for example. Thereby, since the movement of the electrolyte solution from the positive electrode side to the negative electrode side can be more reliably suppressed, the charge / discharge cycle life can be improved more effectively. Moreover, it is preferable that the said ratio is 40% or less, for example. Thereby, the capacity | capacitance fall can be suppressed and also insulation can fully be maintained.

-Short-circuit prevention effect by the porous insulating layer 15 Since the porous insulating layer 15 mainly composed of inorganic oxide has a melting point higher than that of the separator 13, it is stable even at a high temperature. For this reason, since it is harder to dissolve than the separator 13, it is possible to prevent physical contact between the positive electrode active material layer 33 and the negative electrode active material layer 23 even when heat is generated.

<Material of porous insulating layer 15>
The porous insulating layer 15 may be a porous layer mainly composed of an inorganic oxide and having insulating properties. For example, it may be formed using an inorganic oxide and a binder.

The porous insulating layer 15 may have heat resistance. Such a porous insulating layer 15 can be formed using, for example, an inorganic oxide and a heat resistant resin. When the present inventor examined, in a lithium secondary battery using an alloy-based negative electrode active material containing silicon or tin, when an internal short circuit occurs, oxygen generated from the positive electrode 30 overheated by Joule heat at the time of the internal short circuit It was found that the reaction with the alloy-based negative electrode active material was more intense than the reaction with the conventional negative electrode active material (carbon material). For this reason, there is a concern that the above reaction may generate heat rapidly and may reduce the safety of the battery. In addition, when the negative electrode has a columnar structure, the specific surface area of the negative electrode active material is large, which may further increase the heat generation rate. On the other hand, when the porous insulating layer 15 has heat resistance, not only the movement of the electrolytic solution can be suppressed, but also the progress of the internal short circuit can be suppressed when an internal short circuit occurs. Therefore, in addition to the charge / discharge cycle characteristics of the lithium secondary battery, safety can be improved more effectively.

<Configuration of lithium secondary battery>
Next, a more specific configuration of the lithium secondary battery of this embodiment will be described.

FIG. 7 is a cross-sectional view schematically showing an example of the lithium secondary battery of the present embodiment. The illustrated example is a coin-type lithium secondary battery. For simplicity, the same components as those in FIG.

The lithium secondary battery 200 includes an electrode group in which a positive electrode 30, a porous insulating layer 15, a separator 13, and a negative electrode 20 are stacked, a positive electrode lead 18 connected to the positive electrode 30, and a negative electrode lead 19 connected to the negative electrode 20. A gasket 16 and an outer case 17.

Hereinafter, the configuration and manufacturing method of each component of the lithium secondary battery 200 will be described.

<Configuration and manufacturing method of positive electrode 30>
The positive electrode 30 includes a positive electrode current collector 31 and a positive electrode active material layer 33. As the positive electrode current collector 31, those commonly used in this field can be used. For example, a porous or non-porous conductive substrate made of a metal material such as stainless steel, titanium, or aluminum or a conductive resin can be used. Examples of the porous conductive substrate include a mesh body, a net body, a punching sheet, a lath body, a porous body, a foam, a fiber group molded body (nonwoven fabric, etc.), and the like. Examples of the non-porous conductive substrate include a foil, a sheet, and a film. The thickness of the porous or non-porous conductive substrate is not particularly limited, but is, for example, 1 to 500 μm, preferably 1 to 50 μm, more preferably 10 to 40 μm, and particularly preferably 10 to 30 μm.

The positive electrode active material layer 33 contains a positive electrode active material. Moreover, the electrically conductive agent and the binder may be contained as needed.

The positive electrode active material is not particularly limited as long as it is a material that can occlude and release lithium ions, but lithium-containing composite metal oxides, olivine-type lithium phosphate, and the like can be preferably used. The lithium-containing composite metal oxide is a metal oxide containing lithium and a transition metal or a metal oxide in which a part of the transition metal in the metal oxide is substituted with a different element. Here, examples of the different element include Na, Mg, Sc, Y, Mn, Fe, Co, Ni, Cu, Zn, Al, Cr, Pb, Sb, and B. Among these, Mn, Al, Co, Ni, Mg, etc. are preferable. One kind or two or more kinds of different elements may be used. Specific examples of the lithium-containing composite metal oxide, for _{_{_{example, Li x CoO 2, Li x}}} NiO 2, Li x MnO 2, Li x Co m Ni 1-m O 2, Li x Co m M 1-m O n _{_{, Li x Ni 1-m M}} m O n, Li x Mn 2 O 4, Li x Mn 2-m M m O 4, LiMPO 4, Li 2 in MPO ₄ F (wherein, M is Na, Mg, Sc, It represents at least one element selected from the group consisting of Y, Mn, Fe, Co, Ni, Cu, Zn, Al, Cr, Pb, Sb and B. x = 0 to 1.2, m = 0 to 0 .9, n = 2.0 to 2.3). Here, m value which shows the molar ratio of lithium is a value immediately after positive electrode active material preparation, and increases / decreases by charging / discharging. Among these, (wherein, M, x, m and n are the same. Above) the general formula _{_{_{Li x Ni 1-m M m}}} O n lithium-containing composite metal oxide represented by are preferred.

The lithium-containing composite metal oxide can be produced according to a known method. For example, it can be manufactured as follows. First, a composite metal hydroxide containing a metal other than lithium is prepared by a coprecipitation method using an alkali agent such as sodium hydroxide. Next, the composite metal hydroxide is subjected to a heat treatment to obtain a composite metal oxide. Subsequently, a lithium compound such as lithium hydroxide is added to the composite metal oxide and further heat-treated. Thereby, a lithium-containing composite metal oxide is obtained. Specific examples of the olivine type lithium phosphate include LiXPO ₄ (wherein X is at least one selected from the group consisting of Co, Ni, Mn and Fe). As the positive electrode active material, one of the above-described active materials may be used alone, or two or more of them may be used in combination as necessary.

As the conductive agent, those commonly used in the field of lithium secondary batteries can be used. Examples include graphites such as natural graphite and artificial graphite, carbon blacks such as acetylene black, ketjen black, channel black, furnace black, lamp black and thermal black, and conductive fibers such as carbon fiber and metal fiber. It is done. One of these conductive agents may be used alone, or two or more may be used in combination as necessary.

As the binder, those commonly used in the field of lithium secondary batteries can be used. For example, polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyethylene, polypropylene, acrylic rubber, polyvinyl acetate, polyvinyl pyrrolidone, polyether, polyether sulfone, hexafluoropolypropylene, styrene butadiene rubber, modified acrylic Examples thereof include rubber and carboxymethyl cellulose. Among these binders, one kind may be used alone, or two or more kinds may be used in combination as necessary.

The positive electrode active material layer 33 is formed as follows, for example. First, a positive electrode mixture slurry containing a positive electrode active material and having a conductive agent, a binder or the like dissolved or dispersed in an organic solvent is prepared as necessary. Next, the positive electrode mixture slurry is applied to the surface of the positive electrode current collector 31 and dried. As the organic solvent, for example, dimethylformamide, dimethylacetamide, methylformamide, N-methyl-2-pyrrolidone (NMP), dimethylamine, acetone, cyclohexanone and the like can be used. For the preparation of the positive electrode mixture slurry, a general mixer, a disperser, or the like that mixes powder and liquid can be used.

The thickness of the positive electrode active material layer 33 is appropriately selected according to various conditions such as the design performance and application of the lithium secondary battery 200. When the positive electrode active material layer 33 is provided on both surfaces of the positive electrode current collector 31, The total thickness of the positive electrode active material layers 33 formed on both surfaces is preferably about 50 to 150 μm.

<Configuration and manufacturing method of porous insulating layer 15>
As described above, the porous insulating layer 15 contains an inorganic oxide as a main component, and has lithium ion permeability and insulating properties during normal use of the lithium secondary battery. The porous insulating layer 15 may be composed of an inorganic oxide and a binder, or may be composed of an inorganic oxide and a heat resistant resin.

The inorganic oxide contained in the porous insulating layer 15 is not particularly limited as long as it can maintain insulation even when the battery generates heat and is chemically stable in the environment inside the battery. Moreover, if it has a high melting | fusing point, since the effect which prevents the continuation of the internal short circuit with the positive electrode 30 and the negative electrode 20 is also acquired, it is preferable. Examples of the inorganic oxide include alumina (Al ₂ O ₃ ), silica (SiO ₂ ), titania (TiO ₂ ), zirconia (ZrO ₂ ), magnesia (MgO), and yttria (Y ₂ O ₃ ). it can. Among these inorganic oxides, one kind may be used alone, or two or more kinds may be used in combination. The median diameter of the inorganic oxide is preferably 0.05 μm or more and 10 μm or less.

As the binder used for the porous insulating layer 15, PVDF, acrylic rubber particles, PTFE or the like can be used. When PTFE or acrylic rubber particles are used, it is preferably used in combination with carboxymethyl cellulose, polyethylene oxide, modified acrylonitrile rubber or the like as a thickener for paste or slurry. One of these binders and thickeners may be used alone, or two or more thereof may be used in combination.

The heat-resistant resin constituting the porous insulating layer 15 is not particularly limited, but aramid, polyamideimide, cellulose and the like can be used. A heat resistant resin may be used individually by 1 type, and may be used in combination of 2 or more type. Moreover, you may use combining a heat resistant resin and other resin.

The porosity of the porous insulating layer 15 is preferably 30% or more and 70% or less, more preferably 40% or more and 70% or less, in view of ion permeability, mechanical strength, and insulation. . “Porosity” is the ratio of the volume of pores existing in the porous insulating layer 15 to the volume of the porous insulating layer 15. It is preferable that the porosity of the porous insulating layer 15 be equal to or higher than the porosity of the separator 13 described later. More preferably, it is higher than the porosity of the separator 13. Thereby, since more electrolyte solution can be hold | maintained at the porous insulating layer 15, the quantity of the electrolyte solution discharged | emitted out of the system by charge can be reduced.

Since the porous insulating layer 15 containing an inorganic oxide and a binder has a relatively high mechanical strength, the durability is high. The content ratio of the inorganic oxide in the porous insulating layer 15 is, for example, 80 to 95% by weight or more.

The porous insulating layer 15 may contain a heat resistant resin in a ratio exceeding 20% by weight, for example. The porous insulating layer 15 containing a heat resistant resin and an inorganic oxide (for example, less than 80% by weight) can have a good balance between flexibility and durability. In such a porous insulating layer 15, the heat-resistant resin contributes to flexibility, and the inorganic oxide having high mechanical strength contributes to durability.

In the present embodiment, the porous insulating layer 15 is formed on the surface of any one of the positive electrode active material layer 33 of the positive electrode 30, the negative electrode active material layer 23 of the negative electrode 20, and the resin porous film serving as the separator 13. It can be formed by casting the raw material of the layer. A plurality of porous insulating layers may be formed by casting the raw material of the porous insulating layer on any two or more of the above surfaces. For example, when a porous insulating layer is formed on the surfaces of the positive electrode active material layer 33 and the separator 13, two porous insulating

layers

15a and 15b are provided between the positive electrode 30 and the negative electrode 20, as shown in FIG. it can.

The porous insulating layer 15 may be an independent sheet. In that case, it can be formed by casting the raw material on a porous sheet. The independent sheet-like porous insulating layer 15 is disposed between the positive electrode 30 and the resin porous film (separator 13) or between the negative electrode 20 and the resin porous film (separator 13). A plurality of porous insulating layers 15 may be disposed between the positive electrode 30 and the negative electrode 20.

The porous insulating layer 15 may be disposed between the positive electrode 30 and the negative electrode 20, but is preferably disposed between the separator 13 and the positive electrode 30. Thereby, the separator 13 exists between the porous insulating layer 15 and the negative electrode 20, and the porous insulating layer 15 is hardly affected by the expansion / contraction of the negative electrode active material. Can be prevented. Further, since the porous insulating layer 15 is disposed adjacent to the positive electrode active material layer 33, the stress applied to the positive electrode active material layer 33 can be more reliably reduced.

The porous insulating layer 15 is preferably disposed on the surface of the separator 13 on the positive electrode side or the negative electrode side, or on the surface of the positive electrode 30. In this case, it is preferable that the porous insulating layer 15 is integrally formed on the separator 13 or is integrally formed by coating the surface of the positive electrode active material layer 33. Thereby, a manufacturing process can be simplified rather than the case where the porous insulating layer 15 is formed independently.

The porous insulating layer 15 may be integrally formed on the surface of the negative electrode active material layer 23. However, if the porous insulating layer 15 is formed on the surface of the negative electrode active material layer 23, the mechanical properties may not be maintained due to expansion / contraction of the alloy-based active material. In addition, a part of the porous insulating layer 15 may enter the space in the negative electrode active material layer 23 (the space between the active material bodies), thereby impairing the original function.

Hereinafter, a method for forming the porous insulating layer 15 will be described more specifically.

First, an inorganic oxide and a binder are mixed with a liquid component to prepare a paste or slurry. The binder is preferably 0.5 to 10 parts by weight per 100 parts by weight of the inorganic oxide, but is not particularly limited. The inorganic oxide, the binder and the liquid component are mixed using, for example, a double kneader. The obtained paste or slurry is applied onto at least one surface of the porous resin film that becomes the positive electrode 30, the negative electrode 20, and the separator 13. The paste or slurry can be applied using, for example, a doctor blade or a die coat. Thereafter, the liquid component contained in the paste or slurry is removed by drying. In this way, the porous insulating layer 15 is obtained.

Alternatively, the porous insulating layer 15 may be formed using an inorganic oxide and a heat resistant resin. In this case, first, a resin solution in which a heat resistant resin is dissolved in a solvent is prepared. The solvent for dissolving the heat-resistant resin is not particularly limited, but is preferably a polar solvent such as N-methyl-2-pyrrolidone (hereinafter abbreviated as NMP). In the resin solution, 500 g or less (preferably 33 g to 300 g) of inorganic oxide may be dispersed per 100 g of heat resistant resin. Next, the resin solution is applied on at least one surface of the positive electrode 30, the negative electrode 20, and the porous resin film. Thereafter, the solvent is removed by drying to obtain a porous insulating layer 15 containing a heat resistant resin.

<Configuration and Production Method of Negative Electrode 20>
The negative electrode 20 includes a negative electrode current collector 21 and a negative electrode active material layer 23. As the negative electrode current collector 21, those commonly used in the field of lithium secondary batteries can be used. For example, a porous or non-porous conductive substrate made of a metal material such as stainless steel, titanium, nickel, copper, or a conductive resin can be used. Examples of the porous conductive substrate include a mesh body, a net body, a punching sheet, a lath body, a porous body, a foam, a fiber group molded body (nonwoven fabric, etc.), and the like. Examples of the non-porous conductive substrate include a foil, a sheet, and a film. The thickness of the porous or non-porous conductive substrate is not particularly limited, but is usually 1 to 500 μm, preferably 1 to 50 μm, more preferably 10 to 40 μm, and particularly preferably 10 to 30 μm. Further, as will be described later, the surface of the negative electrode current collector 21 is provided with a plurality of convex portions.

The negative electrode active material layer 23 contains an alloy-based active material and is formed in a thin film on one or both surfaces of the negative electrode current collector 21. Moreover, the negative electrode active material layer 23 may contain a well-known negative electrode active material, an additive, etc. in the range which does not impair the characteristic with an alloy type active material. Furthermore, the thickness of the negative electrode active material layer 23 (thickness when the negative electrode active material layer 23 is formed) is preferably 3 to 50 μm. The negative electrode active material layer 23 is preferably amorphous or low crystalline.

The alloy-based active material is a negative electrode active material that occludes lithium by alloying with lithium during charging and releases lithium during discharging. It does not restrict | limit especially as an alloy type active material, A well-known thing can be used. For example, a silicon containing compound, a tin containing compound, etc. are mentioned. Examples of the silicon-containing compound include silicon, silicon oxide, silicon nitride, silicon-containing alloy, silicon compound and its solid solution. Examples of the silicon oxide include silicon oxide represented by the composition formula: SiOα (0 <α <2). Examples of silicon carbide include silicon carbide represented by the composition formula: SiCβ (0 <β <1). Examples of the silicon nitride include silicon nitride represented by the composition formula: SiNγ (0 <γ <4/3). Examples of the silicon-containing alloy include an alloy containing silicon and one or more elements selected from the group consisting of Fe, Co, Sb, Bi, Pb, Ni, Cu, Zn, Ge, In, Sn, and Ti. . Further, a part of silicon is selected from the group consisting of B, Mg, Ni, Ti, Mo, Co, Ca, Cr, Cu, Fe, Mn, Nb, Ta, V, W, Zn, C, N, and Sn. It may be substituted with one or more elements. Among these, it is particularly preferable to use SiOα (0 <α <2) which is excellent in reversibility of charge / discharge.

Examples of the tin-containing compound include tin, tin oxide, tin nitride, tin-containing alloy, tin compound and its solid solution, and the like. Examples of tin-containing compounds include tin, tin oxides such as SnOδ (0 <δ <2), SnO ₂ , Ni—Sn alloys, Mg—Sn alloys, Fe—Sn alloys, Cu—Sn alloys, and Ti—Sn. Tin-containing alloys such as alloys, tin compounds such as SnSiO ₃ , Ni ₂ Sn ₄ and Mg ₂ Sn can be preferably used. Among these, tin and tin oxides such as SnOβ (0 <β <2) and SnO ₂ are particularly preferable.

The negative electrode active material layer 23 is an aggregate of a plurality of columnar bodies (active material bodies) containing an alloy-based active material. As described above with reference to FIG. 1, these active material bodies contain an alloy-based active material and are arranged on the surface of the negative electrode current collector 21 with a space therebetween. Each active material body extends from the surface of the negative electrode current collector 21 in a direction away from the surface of the negative electrode current collector 21. Preferably, the plurality of active material bodies are formed to extend in the same direction. Such a negative electrode active material layer 23 can be manufactured by providing a plurality of convex portions on the surface of the negative electrode current collector 21 and forming an active material body on each of the convex portions.

Here, a more detailed configuration of the negative electrode 20 will be described with reference to FIGS. 8 and 9. FIG. 8 is an enlarged cross-sectional view illustrating a part of the negative electrode 20. For simplicity, FIG. 8 shows only one active material body. FIG. 9 is a schematic perspective view of the negative electrode current collector 21.

As shown in FIG. 9, the negative electrode current collector 21 has a plurality of convex portions 22 on the surface (surface on which the negative electrode active material layer is to be formed) 21a. Although not shown, the convex portion 22 may be similarly provided on the surface opposite to the surface 21a.

The convex portion 22 is a protrusion that extends from the surface 21 a of the negative electrode current collector 21 in a direction away from the negative electrode current collector 21. The convex portions 22 may be randomly arranged, or may be regularly arranged as illustrated. It is preferable that the convex portions 22 are regularly arranged because the size of the space formed between the active material bodies 24 can be easily controlled by the pitch and size of the convex portions 22.

The height (average height) h of the convex portion 22 is not particularly limited, but is preferably 3 μm or more. If it is 3 micrometers or more, when forming the active material body 24 by the oblique vapor deposition mentioned later, the active material body 24 can be selectively arrange | positioned on the convex part 22 more reliably using a shadowing effect. Therefore, a sufficient space can be secured between the active material members 24. On the other hand, the height h of the convex portion 22 is preferably 10 μm or less. If the convex part 22 is 10 micrometers or less, since the volume ratio of the electrical power collector 11 which occupies for an electrode can be restrained small, it becomes possible to obtain a high energy density. In the present specification, the height (average height) h of the convex portion 22 is perpendicular to the surface 21 a of the negative electrode current collector 21 and includes a vertex of the convex portion 22. The height from the surface 21a to the apex of the convex part 22, that is, the length of the perpendicular dropped from the apex of the convex part 22 to the surface 21a. “A vertex of the convex portion 22” refers to the highest point with respect to the surface 21 a of the negative electrode current collector 21. The “surface 21a” refers to the surface of the surface of the negative electrode current collector 21 where the convex portions 22 are not formed. The average height of the convex portions 22 is obtained by, for example, observing a cross section of the negative electrode 20 perpendicular to the surface of the negative electrode current collector 21 with a scanning electron microscope (SEM), and measuring the height of the 100 convex portions 22. , By calculating an average value thereof.

Further, the cross-sectional diameter r of the convex portion 22 is not particularly limited, but is preferably 1 μm or more, for example. Thereby, the contact area of the convex part 22 and the active material body 24 is fully securable. On the other hand, the cross-sectional diameter r is preferably 50 μm or less. When the cross-sectional diameter r is larger than 50 μm, there may be a case where sufficient voids cannot be formed between the active material bodies 24. Note that the cross-sectional diameter r of the convex portion 22 indicates the maximum width of the convex portion 22 in a direction parallel to the surface 21 a in a cross section that is perpendicular to the surface of the negative electrode current collector 21 and includes the apex of the convex portion 22. Similarly to the height h of the convex portion 22, the cross-sectional diameter r of the convex portion 22 can also be obtained by measuring the width of 100 convex portions 22 and calculating the average value of these measured values. The plurality of convex portions 22 may not all have the same height h or the same cross-sectional diameter r.

In the example shown in FIG. 8, the shape of the convex part 22 seen from the normal line direction of the negative electrode 20 is circular. The shape of the convex part 22 here is a convex part as viewed from above in the vertical direction when the current collector 21 is placed so that the surface opposite to the surface 21a of the negative electrode current collector 21 coincides with the horizontal plane. 22 shapes. In addition, the shape of the convex part 22 is not limited to a circle, For example, a polygon, an ellipse, a parallelogram, a trapezoid, a rhombus, etc. may be sufficient.

The convex portion 22 preferably has a substantially planar apex p at the tip portion in the extending direction. In the illustrated example, the convex portion 22 has a circular top portion p. When the convex part 22 has the planar top part p, the bondability of the convex part 22 and the active material body 24 will improve. It is further preferable that the planar apex p is substantially parallel to the surface 21a, since the bonding strength between the convex portion 22 and the active material body 24 can be further increased.

The number of protrusions 22 per unit area, the interval between the protrusions 22, and the like are not particularly limited, and the size (height, cross-sectional diameter, etc.) of the protrusions 22 and the active material body 24 provided on the surface of the protrusions 22. It is appropriately selected according to the size of the. The number of convex portions 22 per unit area is, for example, about 10,000 to 10 million pieces / cm ² . Moreover, it is preferable that the inter-axis distance d of the adjacent convex part 22 is about 2 micrometers or more and about 100 micrometers, for example.

The convex portions 22 are preferably arranged regularly at a predetermined arrangement pitch, and may be arranged in a pattern such as a houndstooth pattern or a grid pattern. The arrangement pitch of the protrusions 22 (the distance between the centers of the adjacent protrusions 22) is, for example, not less than 10 μm and not more than 100 μm. Here, the “center of the convex portion 22” refers to the center point of the maximum width on the upper surface (top portion) of the convex portion 22. If the arrangement pitch is 10 μm or more, a space for expanding the active material members 24 can be more reliably secured between the adjacent active material members 24. On the other hand, when the arrangement pitch is 100 μm or less, a high capacity can be secured without increasing the height of the active material body 24.

Further, it is preferable that the ratio of the interval between the protrusions 22 to the arrangement pitch of the protrusions 22 is 1/3 or more and 2/3 or less. If the spacing ratio is 1/3 or more, when the active material bodies 24 are formed on the respective convex portions 22, the widths of the gaps in the active material bodies 24 in the respective arrangement directions of the convex portions 22 are more reliably ensured. It can be secured. On the other hand, when the proportion of the spacing is larger than 2/3, the active material is also present in the spacing (also referred to as “concave portion” or “groove”) between the convex portions 22 when forming the active material body by oblique deposition. As a result, the expansion stress applied to the negative electrode current collector 21 may increase.

Furthermore, when the convex portion 22 is a columnar body having a side surface perpendicular to the surface of the negative electrode current collector 21, in the cross-sectional view of the negative electrode 20, the interval between the adjacent convex portions 22 is the width of the convex portion 22. It is preferable that it is 30% or more. As a result, a sufficient gap can be secured between the active material members 24 to significantly relieve the expansion stress. On the other hand, if the distance between the adjacent convex portions 22 is too large, the thickness of the negative electrode active material layer 23 increases in order to ensure capacity. Therefore, in the cross section of the negative electrode 20, the interval between the protrusions 22 is preferably 250% or less of the width of the protrusions 22.

A protrusion (not shown) may be formed on the surface of the convex portion 22 by plating or the like. Thereby, since the joining property of the convex part 22 and the active material body 24 can be improved effectively, peeling from the convex part 22 of the active material body 24, peeling propagation, etc. can be prevented more reliably. The protrusion is provided so as to protrude from the surface of the protrusion 22 to the outside of the protrusion 22. The width and height of the protrusions are smaller than the width and height of the protrusions 22, and a plurality of protrusions may be formed on the surface of each protrusion 22. Furthermore, protrusions may be formed on the side surfaces of the protrusions 22 so as to extend in the circumferential direction and / or the growth direction of the protrusions 22. Moreover, when the convex part 22 has a planar top part, one or more protrusions smaller than the convex part 22 may be formed in each top part. The protrusion formed on the top may extend in one direction.

The upper surface of the convex portion 22 may be flat, but preferably has irregularities. The unevenness can be formed, for example, by forming a protrusion on the upper surface of the convex portion 22 as described above. The surface roughness Ra of the upper surface of the convex portion 22 is preferably 0.3 μm or more and 5.0 μm or less. As a result, a sufficient adhesion force between the convex portion 22 and the active material body 24 can be ensured, so that the active material body 24 can be prevented from peeling off. “Surface roughness Ra” here refers to “arithmetic average roughness Ra” defined in Japanese Industrial Standards (JISB0601-1994), and can be measured using, for example, a surface roughness meter.

In addition, when the cross section of the concavo-convex pattern formed on the surface of the negative electrode current collector 21 has a curved shape, the boundary between the convex portion 22 and portions other than the convex portion (“groove”, “concave portion”) is not clear. May be. In such a case, a portion having an average height or more of the entire surface having the concavo-convex pattern is referred to as a “projection 22”, and a portion less than the average height is referred to as a “groove” or “concave”. In addition, a plane including the bottom of the recess is referred to as “surface 21a”.

The negative electrode current collector 21 in the present embodiment can be produced by forming irregularities on a current collector material sheet such as a metal foil or a metal sheet. Examples of the method for forming the unevenness include a method of transferring the surface of a roller having a plurality of recesses formed on the surface (hereinafter referred to as “roller processing method”), a photoresist method, and the like.

In the roller processing method, a current collector raw material sheet is mechanically pressed using a roller having a recess formed on the surface (hereinafter referred to as a “projection forming roller”). Thereby, the some convex part 22 can be formed in the at least one surface of the raw material sheet | seat for collectors. As the material sheet for the current collector, a sheet containing the material as described above as the material of the negative electrode current collector 21 can be used.

As shown in FIG. 8, the negative electrode active material layer 23 includes a plurality of columnar active material bodies 24 extending from the surface of the convex portion 22 toward the outside of the negative electrode current collector 21. Each active material body 24 may extend in the normal direction D of the surface 21 a of the negative electrode current collector 21. Alternatively, it may extend in a direction inclined with respect to the normal direction D. Each active material body 24 may have a structure in which a plurality of columnar lumps having different growth directions are stacked.

Each active material member 24 preferably has a gap between adjacent active material members 24 at least before charging. This gap can relieve stress due to expansion and contraction during charging / discharging, so that the active material body 24 is difficult to peel off from the convex portion 22. As a result, deformation of the negative electrode current collector 21 and the negative electrode 20 can be suppressed.

The width of the gap between the active material bodies 24 can be adjusted by the arrangement pitch or size of the protrusions 22. Further, these active material bodies 24 may be arranged immediately after the formation of the negative electrode active material layer 23 or at intervals during discharging, but adjacent active material bodies 24 may come into contact with each other during charging.

The active material body 24 may have a structure in which n (n ≧ 2) layers (columnar blocks) are stacked. A larger number n is more preferable. For example, as shown in FIG. 10, it may be a columnar product in which eight

columnar chunks

24a, 24b, 24c, 24d, 24e, 24f, 24g, and 24h are laminated.

The negative electrode active material layer 23 including such an active material body 24 is formed as follows. First, the columnar chunk 24a is formed so as to cover the top of the convex portion 22 and a part of the side surface following the top. Next, the columnar chunk 24b is formed so as to cover the remaining side surface of the convex portion 22 and a part of the top surface of the columnar chunk 24a. That is, in the cross-sectional view shown in FIG. 10, the columnar chunk 24a is formed at one end including the top of the convex portion 22, the columnar chunk 24b partially overlaps the columnar chunk 24a, but the remaining portion is the convex portion. 22 is formed at the other end. Further, the columnar chunk 24c is formed so as to cover the rest of the top surface of the columnar chunk 24a and a part of the top surface of the columnar chunk 24b. That is, the columnar chunk 24c is formed so as to mainly contact the columnar chunk 24a. Further, the columnar chunk 24d is formed mainly in contact with the columnar chunk 24b. Similarly, the active material body 24 is formed by alternately stacking the

columnar chunks

24e, 24f, 24g, and 24h.

Next, a method for producing the negative electrode active material layer 23 will be described more specifically. Here, a method of forming the negative electrode active material layer 23 by oblique deposition will be described.

FIG. 11 is a cross-sectional view illustrating an electron beam evaporation apparatus 50 used for forming the negative electrode active material layer 23. In FIG. 11, each member inside the vapor deposition apparatus 50 is also indicated by a solid line.

The vapor deposition apparatus 50 includes a chamber 51, a first pipe 52, a fixing base 53, a nozzle 54, a target (evaporation source) 55, an electron beam generator not shown, a power source 56, and a second pipe not shown. The chamber 51 is a pressure-resistant container-like member having an internal space, and a first pipe 52, a fixing base 53, a nozzle 54, and a target 55 are accommodated therein. The first pipe 52 supplies the source gas to the nozzle 54. One end of the first pipe 52 is connected to the nozzle 54. The other end of the first pipe 52 extends to the outside of the chamber 51 and is connected to a source gas cylinder or a source gas manufacturing apparatus (not shown) via a mass flow controller (not shown). As source gas, oxygen, nitrogen, etc. can be used, for example.

The fixing base 53 is a plate-like member, and is supported so as to be angularly displaced or rotatable with respect to the horizontal plane 60. The negative electrode current collector 21 is fixed to one surface of the fixing base 53. For example, in FIG. 11, the position of the fixing base 53 is switched between a first position indicated by a solid line and a second position indicated by a one-dot broken line, whereby the deposition angle can be switched.

The first position is that the surface of the fixing base 53 on the side where the negative electrode current collector 21 is fixed is opposed to the nozzle 54 below in the vertical direction, and the angle between the fixing base 53 and the horizontal plane 60 is α °. Position. The second position is such that the surface of the fixing base 53 on the side where the negative electrode current collector 21 is fixed is opposed to the nozzle 54 below in the vertical direction, and the angle formed by the fixing base 53 and the horizontal plane 60 is (180−α). It is a position that becomes °. The angle α ° is appropriately selected according to the dimensions of the active material body 24 to be formed.

The nozzle 54 is provided between the fixed base 53 and the target 55 in the vertical direction. The nozzle 54 mixes the vapor of evaporation material such as an alloy-based active material that evaporates from the target 55 and rises upward in the vertical direction, and the raw material gas supplied from the first pipe 52, and the surface of the fixed base 53. To the surface of the negative electrode current collector 21 fixed to the surface.

The target 55 accommodates an alloy-based negative electrode active material or its raw material. The electron beam generator irradiates and heats an alloy-based active material accommodated in the target 55 or its raw material with an electron beam to generate these vapors. The power source 56 is provided outside the chamber 51 and is electrically connected to the electron beam generator, and applies a voltage for generating an electron beam to the electron beam generator. The second pipe introduces a gas that becomes the atmospheric gas in the chamber 51.

A method for forming the negative electrode active material layer 23 using the electron beam evaporation apparatus 50 shown in FIG. 11 will be described.

First, the negative electrode current collector 21 is fixed to the fixing base 53, and the fixing base 53 is set to the first position. Oxygen gas is introduced into the chamber 51 using the second pipe 52 and the nozzle 54. In this state, the alloy-based negative electrode active material of the target 55 or its raw material is irradiated with an electron beam and heated to generate its vapor. In the present embodiment, SiOα (0 <α <2) is used as the alloy-based active material. The generated silicon vapor rises upward in the vertical direction, and is mixed with oxygen supplied from the nozzle 54 when passing through the nozzle 54. Thereafter, the silicon vapor and oxygen are further raised and supplied to the surface of the negative electrode current collector 21 fixed to the fixed base 53.

On the surface of the negative electrode current collector 21, silicon vapor and oxygen gas react to grow silicon oxide. In the present embodiment, silicon atoms fly toward the surface of the negative electrode current collector 21 from a direction inclined by an angle ω ₁ (deposition angle) with respect to the normal direction of the negative electrode current collector 21. The oxygen is supplied from the nozzle 54 near the surface of 21. Thereby, silicon oxide is deposited on the surface of the negative electrode current collector 21. The vapor deposition angle ω ₁ is equal to the angle α formed by the fixed base 53 and the horizontal plane 60. The direction in which oxygen is supplied is not particularly limited. Here, oxygen is supplied to the surface of the negative electrode current collector 21 from the back of the sheet of FIG.

When the material of the evaporation source (silicon) is incident from a direction inclined with respect to the normal direction of the negative electrode current collector 21 (oblique deposition), it is easy to deposit on the convex portion on the surface of the negative electrode current collector 21, and the convex portion The silicon oxide grows in a columnar shape selectively only on the top. On the other hand, silicon atoms do not enter the portion of the surface of the negative electrode current collector 21 that is shadowed by the silicon oxide that grows in a columnar shape, and silicon oxide is difficult to deposit (shadowing effect). In this way, the columnar mass 24a of the active material body shown in FIG. 10 is formed.

Next, the fixed base 53 is rotated and set to the second position, and silicon oxide is grown in the same manner as described above. At this time, silicon atoms and oxygen gas are introduced to the surface of the negative electrode current collector 21 from a direction inclined to the opposite side of the vapor deposition direction when forming the columnar mass 24 a with respect to the normal direction of the negative electrode current collector 21. Incident. When the deposition angle with respect to the normal direction of the negative electrode current collector 21 is ω ₂ , ω ₁ = −ω ₂ . Thereby, the columnar chunk 24b (FIG. 10) is formed on the columnar chunk 24a.

In this way, by alternately switching the position of the fixing base 53 between the first position and the second position, as shown in FIG. 10, an active material body composed of a plurality of columnar chunks 24a to 24h The negative electrode active material layer 23 containing 24 can be formed.

In the active material body 24 formed by the above method, the growth direction of the columnar mass 24 a is inclined by the angle θ _{1 with} respect to the normal direction D of the negative electrode current collector 21. The inclination angle θ ₁ is determined by the deposition angle (silicon incident angle) ω ₁ . Specifically, it is empirically known that the inclination angle θ ₁ in the growth direction and the deposition angle ω _{1 of} silicon satisfy the relationship of 2 tan θ ₁ = tan ω ₁ . It is also known that the inclination angle calculated from the above relational expression is lowered by controlling the pressure in the vacuum chamber by changing the oxygen introduction amount. Therefore, the inclination angle θ ₁ can be controlled by changing the deposition angle ω ₁ and the vacuum chamber internal pressure. The growth direction of the columnar chunk 24 b is inclined by an angle θ _{2 in} the direction opposite to the growth direction of the columnar chunk 24 a with respect to the normal direction D of the negative electrode current collector 21. As described above, when the deposition direction is switched so that the deposition material is alternately incident from the opposite side with respect to the normal direction D of the negative electrode current collector 21 during the deposition, the growth directions of the plurality of columnar chunks 24a to 24h are changed. Are alternately inclined in the opposite direction with respect to the normal direction D of the negative electrode current collector 21.

The active material body 24 formed by the above method has a chemical composition of SiO _x . The average value of the molar ratio x of the oxygen amount to the silicon amount is greater than 0 and less than 2. Note that the active material body 24 may be formed so that an oxygen concentration gradient is formed in the thickness direction of the active material body 24. Specifically, the oxygen content may be increased in a portion close to the negative electrode current collector 21, and the oxygen content may be reduced as the distance from the negative electrode current collector 21 increases. In general, in an active material containing silicon oxide, the higher the oxygen content, that is, the closer x is to 2, the smaller the volume expansion coefficient of the active material due to occlusion of lithium. On the other hand, the volume capacity density (mAh / cm ³ ) can be increased as the oxygen content is lower, that is, as x is closer to zero, but the volume expansion coefficient is increased. Therefore, in the active material body 24 having the oxygen concentration gradient as described above, the expansion / shrinkage of the active material can be suppressed in the portion close to the negative electrode current collector 21, so that the bonding between the convex portion 22 and the active material body 24 is performed. The sex can be further improved. Moreover, in the part away from the negative electrode collector 21, since the oxygen content is small, the volume capacity density is high.

In addition, the formation method of the active material body 24 is not limited to the method mentioned above. For example, the raw material gas may not be supplied from the nozzle 54 and the active material body 24 mainly composed of silicon or tin may be formed. Further, vapor deposition may be performed with a constant deposition angle without switching. Thereby, the active material body 24 grown along one direction is obtained. Further, during the vapor deposition, the vapor deposition angle may be changed by rotating the fixed base 53 along the rotation axis to change the installation direction of the negative electrode current collector 21.

Furthermore, in the above method, eight times of vapor deposition are performed while switching the vapor deposition angle, but the number of times of vapor deposition is not particularly limited. For example, when the vapor deposition angle is alternately switched between 60 ° and −60 °, for example, and vapor deposition is performed up to the n-th stage (n ≧ 2), the active material body 24 having n portions can be formed.

In this embodiment, the negative electrode active material layer is formed using oblique vapor deposition, but lift-off as described in Patent Document 3 can be used instead. Alternatively, a negative electrode active material layer having a columnar structure may be formed by depositing an active material film and then patterning.

<Separator 13>
As the separator 13, a sheet or film having characteristics such as predetermined ion permeability, mechanical strength, and insulating properties are used. Specific examples of the separator 13 include porous sheets or films such as a microporous film, a woven fabric, and a non-woven fabric. The microporous film may be either a single layer film or a multilayer film. Although various resin materials can be used as the material of the separator 13, it is preferable to use polyolefins such as polyethylene and polypropylene in consideration of durability, shutdown function, battery safety, and the like. The thickness of the separator 13 is generally 10 to 300 μm, preferably 10 to 40 μm, more preferably 10 to 30 μm, and further preferably 10 to 25 μm. The porosity of the separator 13 is preferably 30 to 70%, more preferably 35 to 60%.

<Electrolyte>
As the electrolytic solution (nonaqueous electrolyte) used in the present embodiment, a nonaqueous electrolyte having lithium ion conductivity is suitably used. The non-aqueous electrolyte may be, for example, a liquid non-aqueous electrolyte, a gel-like non-aqueous electrolyte, a solid electrolyte (for example, a polymer solid electrolyte), or the like.

The liquid non-aqueous electrolyte contains a solute (supporting salt) and a non-aqueous solvent, and further contains various additives as necessary. Solutes usually dissolve in non-aqueous solvents.

As the solute, those commonly used in this field can be used. For example, LiClO ₄ , LiBF ₄ , LiPF ₆ , LiCF ₃ SO ₃ , LiCF ₃ CO ₂ , LiBr, LiI, LiBCl ₄ , borate salts, imide salts and the like can be mentioned. Examples of borates include lithium bis (1,2-benzenediolate (2-)-O, O ′) borate, bis (2,3-naphthalenedioleate (2-)-O, O ′) boric acid. Lithium, bis (2,2′-biphenyldiolate (2-)-O, O ′) lithium borate, bis (5-fluoro-2-olate-1-benzenesulfonic acid-O, O ′) lithium borate Etc. Examples of imide salts include lithium bistrifluoromethanesulfonate imide ((CF ₃ SO ₂ ) ₂ NLi), lithium trifluoromethanesulfonate nonafluorobutanesulfonate ((CF ₃ SO ₂ ) (C ₄ F ₉ SO ₂ ) NLi) ), Lithium bispentafluoroethanesulfonate imide ((C ₂ F ₅ SO ₂ ) ₂ NLi), and the like. One of the above solutes may be used alone, or two or more may be used in combination as necessary. The amount of the solute dissolved in the non-aqueous solvent is preferably in the range of 0.5 to 2.0 mol / L.

As the non-aqueous solvent, those commonly used in this field can be used. For example, cyclic carbonate ester, chain carbonate ester, cyclic carboxylic acid ester and the like can be mentioned. Examples of the cyclic carbonate include propylene carbonate (PC) and ethylene carbonate (EC). Examples of the chain carbonate include diethyl carbonate (DEC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), and the like. Examples of the cyclic carboxylic acid ester include γ-butyrolactone (GBL) and γ-valerolactone (GVL). One of the non-aqueous solvents may be used alone, or two or more may be used in combination as necessary.

The gel-like non-aqueous electrolyte includes a liquid non-aqueous electrolyte and a polymer material that holds the liquid non-aqueous electrolyte. The polymer material used here is capable of gelling a liquid material. As the polymer material, those commonly used in this field can be used. Examples thereof include polyvinylidene fluoride, polyacrylonitrile, polyethylene oxide, polyvinyl chloride, polyacrylate, and polyvinylidene fluoride.

The solid electrolyte includes, for example, a solute (supporting salt) and a polymer material. Solutes similar to those exemplified above can be used. Examples of the polymer material include polyethylene oxide (PEO), polypropylene oxide (PPO), a copolymer of ethylene oxide and propylene oxide, and the like.

<Positive electrode and negative electrode lead, outer case>
One end of the positive electrode lead 18 is connected to the positive electrode current collector 31, and the other end is led out from the opening 17 a of the outer case 17 to the outside of the lithium secondary battery 1. One end of the negative electrode lead 19 is connected to the negative electrode current collector 12 a, and the other end is led out of the lithium secondary battery 1 from the opening 17 b of the outer case 17. As the positive electrode lead 14 and the negative electrode lead 19, any one commonly used in the technical field of lithium secondary batteries can be used. Further, the

openings

17 a and 17 b of the outer case 17 are sealed with a gasket 16. For the gasket 16, for example, various resin materials can be used. As the outer case 17, any one commonly used in the technical field of lithium secondary batteries can be used. Instead of using the gasket 16, the

openings

17a and 17b of the outer case 17 may be directly sealed by welding or the like.

<Method for Manufacturing Lithium Secondary Battery 200>
The lithium secondary battery 200 can be manufactured, for example, as follows. Here, a case where the porous insulating layer 15 is integrally formed with the positive electrode 30 will be described as an example.

First, the negative electrode 20, the positive electrode 30, and the separator 13 are prepared. The porous insulating layer 15 is integrally formed on the surface of the positive electrode active material layer 33 in the positive electrode 30.

Next, one end of the positive electrode lead 18 is connected to a portion of the surface of the positive electrode current collector 31 of the positive electrode 30 where the positive electrode active material layer 33 is not formed. Similarly, one end of the negative electrode lead 19 is connected to a portion of the surface of the negative electrode current collector 21 of the negative electrode 20 where the negative electrode active material layer 23 is not formed.

Thereafter, the positive electrode 30 and the negative electrode 20 are laminated via the separator 13 to produce an electrode group. At this time, the positive electrode 30, the negative electrode 20, and the separator 13 are disposed so that the positive electrode active material layer 33 and the negative electrode active material layer 23 face each other.

The obtained electrode group is inserted into the outer case 17 together with the electrolyte, and the other ends of the positive electrode lead 18 and the negative electrode lead 19 are led out of the outer case 17. In this state, the

openings

17 a and 17 b are welded through the gasket 16 while the inside of the outer case 17 is vacuum-depressurized. In this way, the lithium secondary battery 200 is obtained.

In addition, the structure and manufacturing method of the lithium secondary battery of this embodiment are not limited to the structure and method mentioned above. Although FIG. 7 shows a lithium secondary battery having a stacked electrode group, the lithium secondary battery of this embodiment may be a cylindrical battery or a square battery having a wound electrode group. Good.

(Example A: Examples 1 to 5 and Comparative Examples 1 and 2)
Lithium secondary batteries having porous insulating layers (Examples 1 to 5) and lithium secondary batteries having no porous insulating layer (Comparative Examples 1 and 2) were produced. Characteristics were evaluated. Hereinafter, the production methods, evaluation methods, and evaluation results of the lithium secondary batteries of Examples and Comparative Examples will be described.

(A-1) Preparation of lithium secondary batteries of Examples 1 to 5 and Comparative Examples 1 and 2 <Example 1>
(A) Production of positive electrode First, a positive electrode active material was produced by the following method.

An aqueous solution containing nickel sulfate at a concentration of 0.82 mol / liter, an aqueous solution containing cobalt sulfate at a concentration of 0.15 mol / liter, and an aqueous solution containing aluminum sulfate at a concentration of 0.03 mol / liter were prepared. Next, a mixed solution of these aqueous solutions was continuously supplied to the reaction vessel. Thereafter, a precursor of the active material was synthesized while sodium hydroxide was dropped into the reaction tank so that the pH of the aqueous solution in the reaction tank was maintained between 10 and 13. The obtained precursor was sufficiently washed with water and dried. In this way, a hydroxide made of Ni _0.82 Co _0.15 Al _0.03 (OH) ₂ was obtained as a precursor.

The obtained precursor and lithium carbonate were mixed so that the molar ratio of lithium, cobalt, nickel and aluminum (Ni: Co: Ni: Al) was 1: 0.82: 0.15: 0.03 did. The mixture was calcined in an oxygen atmosphere at a temperature of 500 ° C. for 7 hours and pulverized. Next, the pulverized fired product was fired again at a temperature of 800 ° C. for 15 hours. The fired product was pulverized and classified to obtain a positive electrode active material having a composition represented by LiNi _0.82 Co _0.15 Al _0.03 O ₂ .

Next, using the positive electrode active material obtained by the above method, a positive electrode was produced by the following method.

100 g of the positive electrode active material powder is sufficiently mixed with 2 g of acetylene black (conductive agent), 2 g of artificial graphite (conductive agent), 3 g of polyvinylidene fluoride powder (binder) and 50 ml of organic solvent (NMP). A paste was prepared. This positive electrode mixture paste was applied to one side of an aluminum foil (positive electrode current collector) having a thickness of 15 μm. The mixture paste was dried to obtain a positive electrode active material layer.

Thereafter, the aluminum foil on which the positive electrode active material layer was formed was rolled to obtain a positive electrode. The thickness of the positive electrode, that is, the total thickness of the positive electrode current collector and the positive electrode active material layer was set to 128 μm.

(B) Formation of porous insulating layer In Example 1, the porous insulating layer was formed on the surface of the positive electrode active material layer. First, 940 g of alumina powder (manufactured by Sumitomo Chemical Co., Ltd., AKP3000), 750 g of NMP solution (BM-720H (trade name) manufactured by Nippon Zeon Co., Ltd.) containing 8% by weight of polyacrylonitrile modified rubber as a binder, and a dispersion medium A suitable amount of NMP was stirred with a double-arm kneader. Thus, a slurry for forming a porous insulating layer was prepared. Next, the obtained slurry was applied over the entire surface of the positive electrode active material layer on the surface of the positive electrode active material layer. The applied slurry was dried at 100 ° C. for 10 hours under vacuum and reduced pressure to form a porous heat-resistant layer. The thickness of the porous heat-resistant layer was 1 μm. Further, the porosity of the porous heat-resistant layer was 49%.

(C) Production of Negative Electrode In Example 1, a negative electrode current collector having irregularities on the surface was produced by a roller processing method.

First, chromium oxide was sprayed onto the surface of a cylindrical iron roller (diameter: 50 mm) to form a ceramic layer having a thickness of 100 μm. A plurality of recesses having a depth of 8 μm were formed on the surface of the ceramic layer by laser processing. Each recess was circular with a diameter of 12 μm when viewed from above the ceramic layer. At the bottom of each recess, the central portion was substantially planar, and the peripheral edge of the bottom had a rounded shape. In addition, the arrangement of these recesses was a close-packed arrangement in which the distance between the axes of adjacent recesses was 20 μm. In this way, a convex forming roller was obtained.

Next, an alloy copper foil (trade name: HCL-02Z, thickness: 26 μm, manufactured by Hitachi Cable Ltd.) containing zirconia at a ratio of 0.03% by weight with respect to the total amount was placed at 600 ° C. in an argon gas atmosphere. Heating was performed for 30 minutes at a temperature, and annealing was performed.

This alloy copper foil was passed at a pressure of 2 t / cm through a pressure contact portion where two convex forming rollers were pressure contacted. Thereby, both surfaces of alloy copper foil were pressure-molded, and the negative electrode collector which has a some convex part on both surfaces was obtained. When a cross section perpendicular to the surface of the negative electrode current collector was observed with a scanning electron microscope, a plurality of convex portions having an average height of about 8 μm were formed on both surfaces of the negative electrode current collector.

Next, a negative electrode active material layer was formed on the surface of the obtained negative electrode current collector by oblique vapor deposition using an electron beam vapor deposition apparatus 50 shown in FIG. The conditions for vapor deposition are as follows.

First, a negative electrode current collector having a size of 30 mm × 30 mm was fixed to a fixed base. The fixing table has a first position (solid line position shown in FIG. 11) at an angle with respect to the horizontal plane of 60 ° (α = 60 °) and an angle with respect to the horizontal plane of 120 ° (180−α = 120 °) It was set to be switchable between the two positions (the position indicated by the one-dot broken line shown in FIG. 11).

Then, the vapor deposition process was performed 40 times, changing the position of a fixed base alternately between the 1st position and the 2nd position. Deposition conditions are shown below.
Negative electrode active material raw material (evaporation source): silicon, purity 99.9999%, manufactured by High Purity Chemical Laboratory Co., Ltd. Oxygen released from nozzle: purity 99.7%, manufactured by Nippon Oxygen Co., Ltd.
Oxygen release flow rate from nozzle: 40 sccm
Fixing table angle α: 60 °
Electron beam acceleration voltage: -8 kV
Emission: 500mA
Deposition time: 3 minutes × 40 times This formed a negative electrode active material layer containing a plurality of active material bodies on one surface of the negative electrode current collector. Each of the active material bodies had a structure in which 40 columnar lumps were laminated, and was arranged on the corresponding convex part of the negative electrode current collector. Moreover, it grew from the top part of the convex part and the side surface near the top part in the direction in which the convex part extends.

Thereafter, oblique deposition was performed on the opposite surface of the negative electrode current collector in the same manner to form a negative electrode active material layer containing a plurality of active material bodies. Thus, the negative electrode which has a negative electrode active material layer on both surfaces of a negative electrode collector was obtained.

Next, the thickness of the negative electrode active material layer was determined. Here, a cross section perpendicular to the negative electrode current collector in the obtained negative electrode is observed with a scanning electron microscope, and for 10 active material bodies formed on the surface of the convex portion, from the vertex of the convex portion to the vertex of the active material body. The length of each was measured. The average of these was calculated as “the thickness of the negative electrode active material layer”. As a result, the thickness of each negative electrode active material layer was 15 μm. Moreover, when the composition of the negative electrode active material layer was analyzed, the composition of the compound constituting the negative electrode active material layer was all SiO _0.4 .

Next, lithium metal was deposited on the surface of these negative electrode active material layers. This is because lithium metal is deposited to supplement lithium corresponding to the irreversible capacity stored in the negative electrode active material layer during the first charge / discharge.

The vapor deposition of lithium metal was performed using a resistance heating vapor deposition apparatus (manufactured by ULVAC, Inc.) in an argon atmosphere. First, lithium metal was loaded into a tantalum boat in a resistance heating vapor deposition apparatus. Next, the negative electrode was fixed so that one of the negative electrode active material layers formed on both surfaces of the negative electrode current collector faced the tantalum boat. Thereafter, a 50 A current was passed through the tantalum boat in an argon atmosphere to deposit lithium metal. The deposition time was 10 minutes. Subsequently, lithium metal was deposited on the other negative electrode active material layer in the same manner.

(D) Production of laminated battery Next, a laminated lithium secondary battery was produced using the positive electrode and the negative electrode obtained by the above method.

The positive electrode having a porous insulating layer formed on the surface was cut out so that the planar shape of the positive electrode active material layer was a square of 20 mm × 20 mm. In the cut out positive electrode, the positive electrode lead was welded to the portion of the surface of the positive electrode current collector where the positive electrode active material layer was not formed to obtain a positive electrode plate.

Further, the negative electrode after the lithium metal was deposited was cut out so that the planar shape of the negative electrode active material layer was a square of 21 mm × 21 mm and a tab portion of 5 mm × 5 mm was formed at one corner where two sides intersected. In the cut-out negative electrode, the negative electrode active material layer located in the tab portion was peeled off, and the negative electrode lead was welded to the surface of the current collector exposed by peeling of the negative electrode active material layer. In this way, a negative electrode plate was obtained.

Next, the positive electrode plate, the negative electrode plate, and the separator were arranged so that the positive electrode active material layer and the negative electrode active material layer faced each other with the separator interposed therebetween, thereby preparing an electrode group. Specifically, the negative electrode plate was set as the center, and the separator and the positive electrode plate were laminated in this order on both surfaces. A polyethylene microporous membrane (trade name: Hypore, thickness: 16 μm, porosity: 40%, manufactured by Asahi Kasei Co., Ltd.) was used as the separator. The structure of the electrode group obtained in this example is shown in FIG. In FIG. 13, the same reference numerals are given to the same components as those in FIG.

The obtained electrode group was inserted into an outer case made of an aluminum laminate together with 0.5 g of an electrolyte. LiPF ₆ was dissolved at a concentration of 1.4 mol / L in a solvent in which ethylene carbonate (EC), ethyl methyl carbonate (EMC) and diethyl carbonate (DEC) were mixed at a volume ratio of 2: 3: 5 as an electrolyte. A non-aqueous electrolyte was used. The ionic conductivity was 6.5 mS / cm, and the viscosity was 6.2 cP.

Next, the positive electrode lead and the negative electrode lead were led out of the outer case from the opening of the outer case. Then, the opening part of the exterior case was welded, vacuum-reducing the inside of the exterior case. In this way, a lithium secondary battery of Example 1 was obtained.

<Example 2>
A lithium secondary battery having the same configuration (FIG. 13) was produced in the same manner as in Example 1 except that the thickness of the porous insulating layer was 2 μm. The porosity of the porous insulating layer was 48%.

<Example 3>
A lithium secondary battery having the same configuration (FIG. 13) was produced in the same manner as in Example 1 except that the thickness of the porous insulating layer was 4 μm. The porosity of the porous insulating layer was 47%.

<Example 4>
A lithium secondary battery having the same configuration (FIG. 13) was produced in the same manner as in Example 1 except that the thickness of the porous insulating layer was 6 μm. The porosity of the porous insulating layer was 47%.

<Example 5>
In Example 5, instead of forming a porous insulating layer on the positive electrode active material layer, a porous insulating layer was formed on the separator. Other configurations and manufacturing methods of the lithium secondary battery are the same as those of the first embodiment.

In Example 5, a porous insulating layer containing a heat resistant resin and an inorganic oxide was formed on a polyolefin separator. A forming method will be described below.

First, in the reaction vessel, the aramid resin was completely heated and dissolved in NMP to obtain an aramid resin solution. At this time, 6.5 g of dry anhydrous calcium chloride was added per 100 g of NMP. After returning the aramid resin solution to room temperature, 3.2 g of paraphenylenediamine (manufactured by Mitsui Chemicals, Inc.) (hereinafter referred to as PPD) is added per 100 g of the aramid resin solution. Dissolved. The reaction vessel was placed in a constant temperature bath at 20 ° C., and terephthalic acid dichloride (manufactured by Mitsui Chemicals, Inc.) (hereinafter referred to as TPC) was added dropwise little by little over 1 hour. Phenylene terephthalamide (hereinafter referred to as PPTA) was synthesized. At this time, 5.8 g of TPC was added per 100 g of an aramid resin solution containing anhydrous calcium chloride and PPD. Thereafter, the reaction was completed by leaving it in a thermostatic bath for 1 hour, and then replaced with a vacuum bath and stirred for 30 minutes under reduced pressure to deaerate to obtain a polymerization solution. The obtained polymerization solution was further diluted with an NMP solution containing calcium chloride to obtain an aramid resin solution having a PPTA concentration of 1.4 wt%. To this solution, 200 g of alumina particles having an average particle size of 0.1 μm was added per 100 g of aramid resin solid component.

Next, an aramid resin solution after adding alumina particles was thinly applied to one side of a porous polyethylene (polyethylene microporous film) having a thickness of 16 μm with a bar coater. Thereafter, hot air at 80 ° C. was applied to the coated surface to dry the aramid resin solution to obtain a resin film. Subsequently, the resin film was sufficiently washed with pure water to remove calcium chloride and then dried. As a result, a 20 μm thick laminate having a structure in which a porous insulating layer having a thickness of 4 μm and a separator (polyethylene microporous film) having a thickness of 16 μm was laminated was obtained. The average porosity of the porous insulator was 48%.

The above laminate was disposed between the positive electrode plate and the negative electrode plate so that the porous insulating layer and the positive electrode active material layer were opposed to each other to constitute an electrode group. The structure of the electrode group in the lithium secondary battery of Example 5 is shown in FIG. For the sake of simplicity, in FIG. 14, the same components as those in FIG. Using this electrode group, a lithium secondary battery was produced in the same manner as in Example 1.

<Comparative Example 1>
A lithium secondary battery was produced in the same manner as in Example 1 except that the porous insulating layer was not provided. An electrode group in the lithium secondary battery of Comparative Example 1 is shown in FIG.

<Comparative Example 2>
A method similar to Comparative Example 1 except that a polyethylene microporous membrane (separator, trade name: hypopore, thickness: 20 μm, porosity: 42%, manufactured by Asahi Kasei Co., Ltd.) having a thickness of 20 μm is used as the separator. Thus, a lithium secondary battery having the same configuration (FIG. 15) was produced.

In Examples 1 to 5 and Comparative Examples 1 and 2, a plurality of lithium secondary batteries including cells for safety evaluation and charge / discharge cycle characteristic evaluation were manufactured.

(A-2) Evaluation of lithium secondary batteries of Examples 1 to 5 and Comparative Examples 1 and 2 <Charging / Discharging Before Evaluation>
Before the charge / discharge test for evaluation was performed on the lithium secondary batteries for safety evaluation of Examples 1 to 5 and Comparative Examples 1 and 2, the capacity was measured by performing charge / discharge under the following conditions.
Constant current charging: 6mA, end voltage 4.15V
Constant voltage charging: End current 1.5 mA, downtime 20 minutes Constant current discharge: 6 mA, End voltage 2.0 V, downtime 20 minutes Ambient temperature: 25 ° C.

<Pseudo internal short circuit test>
After charging the lithium secondary batteries for safety evaluation of Examples 1 to 5 and Comparative Examples 1 and 2 after measuring the capacity under the same conditions as the above capacity measurement, the pseudo internal short circuit was performed under the following conditions: A test was conducted.

While applying an external voltage of 4.2 V to the lithium secondary battery in a temperature bath set at 25 ° C., an iron nail (diameter: 2 mm) was inserted into the lithium secondary battery at a speed of 0.1 mm / second. Penetrated. The nail penetrated the electrode group along the normal direction of the negative electrode plate, and as a result, a short circuit occurred between the positive electrode and the negative electrode.

In the pseudo internal short circuit test, the battery voltage and current were monitored, and the calorific value (J) for 0.5 seconds from the occurrence of the short circuit was obtained. From the results, the calorific values of the lithium secondary batteries of Examples 1 to 5 when the calorific value of the lithium secondary battery of Comparative Example 1 was set to 100 were calculated. The results are shown in Table 1.

<Charge / discharge cycle life test>
The lithium secondary batteries for charge / discharge cycle characteristics evaluation of Examples 1 to 5 and Comparative Examples 1 and 2 were subjected to a charge / discharge cycle life test under the following conditions to determine the capacity retention rate. Here, the ratio of the capacity at the 400th cycle of the lithium secondary battery to the capacity at the first cycle was determined as the capacity maintenance rate. The results are shown in Table 1.
Constant current charging: 21 mA, end voltage 4.15 V
Constant voltage charging: End current 1.5 mA, downtime 20 minutes Constant current discharge: 30 mA, End voltage 2.0 V, downtime 20 minutes Ambient temperature: 25 ° C.

Further, in the lithium secondary batteries of Examples and Comparative Examples, the volume change (expansion coefficient) due to charging / discharging of the negative electrode active material body was determined, and both were 290%. The volume change of the active material body was (Vc−Vd) / Vd × 100 (%), where Vd is the volume of the active material body during discharge and Vc is the volume of the active material body during charging. Here, the volume Vd of the active material body at the time of discharge is obtained from the thickness and porosity of the negative electrode active material layer at the time of discharge (ratio of the volume occupied by the gap between the active material bodies in the entire negative electrode active material layer). The volume Vc of the negative electrode active material layer during charging was determined from the thickness of the negative electrode active material layer (the porosity of the negative electrode active material layer during charging was zero).

From the results of the pseudo internal short-circuit test shown in Table 1, the amount of heat generated by the lithium secondary battery when an internal short-circuit occurred was determined by providing a porous insulating layer of 1 μm or more on the positive electrode surface (Examples 1 to 5). It turned out that it can reduce from 1 and 2. This is presumably because in the lithium secondary batteries of Examples 1 to 5, the progress of short circuit is suppressed by the porous insulating layer, and the oxidation reaction of the negative electrode is suppressed. Moreover, when the porous insulating layer was thickened, the amount of heat generation tended to be further reduced. Furthermore, it has been found that even when a porous insulating layer is provided on the separator, the amount of heat generation can be reduced.

Further, from the measurement results of the capacity retention ratio shown in Table 1, it was found that the lithium secondary batteries of Examples 1 to 5 had higher charge / discharge cycle characteristics than Comparative Examples 1 and 2. Therefore, it was confirmed that the cycle life of the lithium secondary battery can be improved by providing a porous insulating layer having a thickness of 1 μm or more.

After the charge / discharge cycle test, the lithium secondary batteries of the comparative example and the example were disassembled, and in the comparative example, it was confirmed by visual observation that the positive electrode active material was dropped. On the other hand, in the Examples, the positive electrode active material was hardly removed. Therefore, in the examples, as described above with reference to FIG. 2 and FIG. 3, the porous insulating layer suppresses the falling off of the positive electrode active material due to the volume change of the negative electrode, thereby improving the cycle life. It is thought that. In addition, as described above with reference to FIG. 6, in Examples 1 to 5, it is considered that the decrease in the electrolyte solution on the positive electrode side due to repeated charge and discharge was suppressed by the porous insulating layer. Moreover, when the porous insulating layer was thickened, the charge / discharge cycle characteristics could be further improved. Furthermore, it was confirmed that the same effect was obtained regardless of the position of the porous insulating layer.

In addition, the thickness of the separator in Comparative Example 2 is equal to the total thickness of the separator and the porous insulating layer in Examples 3 and 5 (20 μm). Therefore, it is considered that the capacities of Comparative Example 2 and Examples 3 and 5 are substantially equal. From this, it was also found that by providing the porous insulating layer, the amount of heat generated by an internal short circuit can be suppressed and the charge / discharge cycle characteristics can be improved without reducing the capacity.

<Evaluation of wettability to electrolyte>
The wettability of the surface of the porous insulating layer in the lithium secondary battery of Example 3 and the surface of the positive electrode plate (surface of the positive electrode active material layer) in the lithium secondary battery of Comparative Example 1 (hereinafter simply referred to as “ Abbreviated as “wetability”). Moreover, the wettability of the separator surface in the lithium secondary battery of Example 3 and Comparative Example 1 was determined.

The wettability was evaluated as follows. First, a drop of the electrolyte was dropped on the surface of the test body (positive electrode plate or separator), and the time change rate of the contact angle was measured. The time change rate of the contact angle was calculated from the contact angle immediately after dropping of the electrolytic solution and the contact angle 10 seconds after dropping. Here, the contact angle was measured twice, and the average value was obtained. As the electrolytic solution used in this evaluation test, the electrolytic solution used in Example 3 and Comparative Example 1 was used. In addition, this evaluation test was performed at a temperature of 25 ° C.

Although the wettability of the surface of the negative electrode active material layer was also measured, the wettability of the negative electrode active material layer was extremely high and could not be quantified by the above method.

Table 2 shows the measurement results.

It is considered that the greater the rate of change of the contact angle with time, the higher the electrolyte permeability (ie, the greater the wettability with respect to the electrolyte).

From the results shown in Table 2, the wettability of the separator was lower than the wettability of the positive electrode active material layer and the porous insulating layer. From this, it was found that in the lithium secondary batteries of Example 3 and Comparative Example 1, the action of holding the electrolytic solution by the separator was smaller than that of the porous insulating layer or the positive electrode active material layer. For this reason, in these batteries, the ability to hold the electrolyte solution on the positive electrode side is considered to be determined mainly by the wettability of the porous insulating layer (Example 3) or the positive electrode active material layer (Comparative Example 1).

As shown in Table 2, it was found that the porous insulating layer had higher wettability than the positive electrode active material layer. Therefore, in the lithium secondary battery of Example 3, by providing the porous insulating layer on the positive electrode active material layer, the effect of holding the electrolyte solution on the positive electrode side is enhanced as compared with the lithium secondary battery of Comparative Example 1. It was confirmed.

(Example B: Examples 6 and 7, Comparative Example 3)
In Example B, a lithium secondary battery was produced using an electrolyte different from the electrolyte used in Example A described above, and the charge / discharge cycle characteristics were evaluated.

<Example 6>
As an electrolytic solution, LiPF ₆ was dissolved at a concentration of 1.4 mol / L in a solvent in which ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DMC) were mixed at a volume ratio of 1: 1: 8. A non-aqueous electrolyte was used. The ionic conductivity was 10.7 mS / cm and the viscosity was 2.9 cP.

Further, a porous insulating layer having a thickness of 2 μm was formed on the surface of the positive electrode active material. A lithium secondary battery having the same configuration (FIG. 13) was produced in the same manner as in Example 1 except for the thickness of the electrolytic solution and the porous insulating layer.

<Example 7>
A lithium secondary battery having the same configuration (FIG. 13) was produced in the same manner as in Example 6 except that the thickness of the porous insulating layer was 4 μm.

<Comparative Example 3>
A lithium secondary battery was produced in the same manner as in Example 6 except that the porous insulating layer was not provided. The configuration of the electrode group in Comparative Example 3 is the same as the configuration shown in FIG.

<Evaluation of charge / discharge cycle characteristics>
For the lithium secondary batteries of Examples 6, 7 and Comparative Example 3, the charge / discharge cycle characteristics were evaluated under the same conditions as those in Example A described above. The results are shown in Table 3.

From the results shown in Table 3, it was found that the charge / discharge cycle life can be improved by providing a porous insulating layer regardless of the type of electrolyte.

Also in the lithium secondary batteries of Examples 6 and 7, the wettability of the porous insulating layer is higher than the wettability of the positive electrode active material layer, as in the previous examples. Therefore, it was found that charge / discharge cycle characteristics can be improved by providing a porous insulating layer having high wettability with respect to the electrolyte regardless of the type of the electrolyte.

Further, the capacity retention rates of Examples 6 and 7 were higher than those of Examples 1 to 5. This is because the electrolytes used in Examples 6 and 7 have higher ionic conductivity and lower viscosity than the electrolytes used in Examples 1 to 5, and thus lithium ions can be moved more easily. it is conceivable that.

The lithium secondary battery of the present invention can be used for the same applications as conventional lithium secondary batteries. In particular, it is useful as a power source for portable electronic devices such as personal computers, mobile phones, mobile devices, personal digital assistants (PDAs), portable game devices, and video cameras. In addition, it is expected to be used as a secondary battery for assisting an electric motor, a power tool, a cleaner, a power source for driving a robot, a power source for a plug-in HEV, etc. in a hybrid electric vehicle, a fuel cell vehicle and the like.

100, 200 Lithium secondary battery 30 Positive electrode 31 Positive electrode current collector 33 Positive electrode active material layer 20 Negative electrode 21 Negative electrode current collector 21a Surface of negative electrode current collector (portion where convex portions are not formed)
22 Protrusions 23 Negative electrode active material layer 24 Active material body 13

Separator

15, 15a, 15b Porous insulating layer 18 Positive electrode lead 19 Negative electrode lead 16 Gasket 17 Exterior case 24 Columnar body 50 Electron beam deposition apparatus 51 Chamber 52 First piping 53 Fixed base 54 Nozzle 55 Target 56 Power supply

Claims

A positive electrode having a positive electrode active material capable of inserting and extracting lithium ions;
A negative electrode having a negative electrode active material capable of inserting and extracting lithium ions;
A separator disposed between the positive electrode and the negative electrode;
A lithium secondary battery comprising an electrolyte solution having lithium ion conductivity,
The negative electrode has a negative electrode current collector having a plurality of convex portions on the surface, and a negative electrode active material layer including a plurality of active material bodies formed on the negative electrode current collector,
Each of the plurality of active material bodies is disposed on each convex portion of the negative electrode current collector, and includes an alloy-based active material containing silicon or tin as the negative electrode active material,
A lithium secondary battery further comprising a porous insulating layer mainly composed of an inorganic oxide between the positive electrode and the negative electrode.
2. The lithium secondary battery according to claim 1, wherein a space is formed between each active material body and an adjacent active material body when the lithium secondary battery is discharged.
The lithium secondary battery according to claim 1 or 2, wherein the porous insulating layer is disposed between the positive electrode and the separator.
The lithium secondary battery according to any one of claims 1 to 3, wherein a volume change due to charging / discharging of the plurality of active material bodies is 200% or more.
The lithium secondary battery according to any one of claims 1 to 4, wherein the porous insulating layer has a thickness of 1 µm to 10 µm.
The lithium secondary battery according to any one of claims 1 to 5, wherein wettability of the surface of the porous insulating layer with respect to the electrolytic solution is higher than wettability of the surface of the positive electrode with respect to the electrolytic solution.
The lithium secondary battery according to any one of claims 1 to 6, wherein a porosity of the porous insulating layer is higher than a porosity of the separator.
The lithium secondary battery according to any one of claims 1 to 7, wherein a ratio of a thickness of the porous insulating layer to a thickness of the separator is 5% or more and 40% or less.
The lithium secondary battery according to any one of claims 1 to 8, wherein the porous insulating layer is formed on at least one of a surface of the positive electrode and a surface of the separator.
The lithium secondary battery according to any one of claims 1 to 9, wherein the alloy-based active material is SiOα (0 <α <2).
The active material body has a plurality of layers stacked on each convex portion of the negative electrode current collector, and a growth direction of each of the plurality of layers is relative to a normal direction of the negative electrode current collector. The lithium secondary battery according to claim 1, wherein the lithium secondary battery is alternately inclined in opposite directions.