JP2002015729A - Nonaqueous electrolyte secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a lithium ion secondary battery with good cycle characteristic by preventing a negative active material from turning into fine particles and from desorbing when a metal active material is used as a negative active material. SOLUTION: With a lithium ion secondary battery consisting of a positive electrode, a negative electrode and a separator pinched by both electrodes, a laminated body laminated with a collector 21, a negative active material layer 22 and a coating layer 23 made of carbon material in turn is used as a negative electrode.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a non-aqueous electrolyte secondary battery and an electrode thereof.

[0002]

2. Description of the Related Art In recent years, as electronic devices such as mobile phones and portable personal computers have been reduced in size and demand has increased, higher performance has been required for secondary batteries which are power sources of these electronic devices. As such a secondary battery, a non-aqueous electrolyte battery using a material capable of occluding and releasing lithium, such as a carbon material, as a negative electrode material has been developed and is widely used as a power source for portable electronic devices. This non-aqueous electrolyte secondary battery is different from a conventional battery in that it is lightweight and has a high electromotive force of 4V class, and its excellent performance has attracted attention.

[0003] Therefore, application of the non-aqueous electrolyte secondary battery as a power source for electric vehicles, power tools, cordless cleaners, and the like has been studied. In such applications, higher energy density is required as compared with conventional non-aqueous electrolyte secondary batteries.

A non-aqueous electrolyte secondary battery using a lithium metal, a lithium alloy or the like as an active material of an electrode is expected as a high energy battery, and has been actively researched and developed.

As the positive electrode active material, LiCoO ₂ , Li
Although Mn ₂ O _{4 and the} like have been put to practical use, lithium ion batteries using carbon materials that occlude and release lithium have been widely put into practical use as negative electrode active materials, and lithium metal and lithium alloys have been used for negative electrodes. Secondary batteries have not yet been put to practical use.

[0006] The reason why lithium metal has not been put into practical use is that lithium deteriorates due to the reaction between the nonaqueous electrolyte and the lithium alloy, and desorption occurs due to the generation of dendritic (dendritic) lithium due to repeated charging and discharging. Therefore, there is a problem that the internal short circuit and the cycle life are short. In order to solve such problems, studies have been made to use lithium as an anode active material by alloying lithium. For example, lithium
There are technologies using an aluminum alloy or the like as the negative electrode (for example, JO BesenHard, J. Electroanal. Che
m., 94, 77 (1978).) As part of Al is used, the efficiency can be improved under shallow charge and discharge with a constant amount of electricity. However, when deep charge and discharge are repeated, the negative electrode active material is pulverized due to a change in volume of the electrode, and a part of the negative electrode active material is also detached from the negative electrode. As a result, since the amount of the negative electrode active material in the negative electrode gradually decreases, there is a problem in charge / discharge cycle characteristics.

Further, alloys other than lithium alloys, such as tin-nickel alloys and copper-tin alloys, have been studied as negative electrode active materials for achieving high energy batteries, but cause the same problem as the lithium alloys. Therefore, it has not been put to practical use.

[0008]

As described above, in a conventional nonaqueous electrolyte secondary battery, when a metal material is used as the negative electrode active material, the energy density can be improved, but the cycle characteristics are deteriorated. There was a problem.

The present invention has been made in view of such a problem, and has as its object to provide a nonaqueous electrolyte secondary battery having a high energy density and excellent charge / discharge cycle performance.

[0010]

According to the present invention, there is provided a non-aqueous electrolyte secondary battery comprising a positive electrode having at least a positive electrode active material, a current collector, and an alloy formed on the surface of the current collector to occlude and release an alkali metal. And a non-aqueous electrolyte sandwiched between the positive electrode and the negative electrode, the negative electrode including a negative electrode active material layer having the following formula: and a coating layer made of a carbon material formed on the negative electrode active material layer.

The nonaqueous electrolyte secondary battery of the present invention uses a negative electrode active material layer made of an alloy. By forming a coating layer on the surface of the negative electrode active material layer, it is possible to suppress the alloy from being finely divided.
Even if the negative electrode active material becomes fine particles as a result of repeated charge / discharge of the battery, the negative electrode active material is retained in the electrode by the coating layer, so that a decrease in the negative electrode active material can be suppressed.

In addition, since a carbon material through which an alkali metal such as lithium can pass is used for the coating layer, it does not hinder the anode active material from absorbing and releasing the alkali metal. In addition, since the carbon material itself has the ability to occlude and release alkali metals, it is possible to suppress a decrease in energy density due to the coating layer as compared with the case where the carbon material is coated with another material.

The thickness of the active material layer is 0.01 μm.
It is preferably at least m and at most 50 μm.

It is preferable that the thickness of the coating layer is from 0.1 μm to 200 μm.

The thickness ratio of the negative electrode active material layer to the thickness of the coating layer is preferably 0.01 or more and 0.95 or less.

By increasing the ratio of the negative electrode active material layer and reducing the ratio of the coating layer, the ability of the negative electrode active material to occlude and release the alkali metal can be improved, but the thickness of the coating layer is too small. And the negative electrode active material may not be able to be held. In addition, when the thickness of the coating layer is large, there is a possibility that the permeability of the alkali metal to the negative electrode active material may be reduced.

[0017]

FIG. 1 is a plan view of the left half of a cylindrical nonaqueous electrolyte secondary battery and a vertical cross section of a right half thereof, which will be described below with reference to the drawings.

A cylindrical container 1 made of metal, for example, made of stainless steel and having a bottom has an insulator 12 disposed at the bottom.
The electrode group 3 is housed in the container 1. The electrode group 3 is formed by laminating a positive electrode 4, a separator 5, a negative electrode 6, and another separator 5 in this order on the negative electrode 6
Is wound on the spiral so as to be located on the outside. The separator 5 is, for example, a nonwoven fabric, a polypropylene microporous film, a polyethylene microporous film,
It is formed from a polyethylene-polypropylene microporous laminated film. In addition, since the electrolyte is contained in the container 1, the electrolyte penetrates into the separator 5.

A PTC element 7 having an opening in the center, a safety valve 8 disposed on the PTC element 7, and a hat-shaped positive terminal 9 disposed on the safety valve 8 are provided in an upper opening of the container 1. It is caulked and fixed via an insulating gasket 10. One end of a current collecting lead 11 for the positive electrode is connected to the positive electrode 4, and the other end is connected to the positive electrode terminal 9. The negative electrode 6 is connected to the container 1 as a negative electrode terminal via a negative electrode current collecting lead 13.

In the non-aqueous electrolyte secondary battery according to the present invention, the outer package is made of a laminate film, and the laminate comprising the positive electrode, the negative electrode and the separator is flatly wound inside the outer package. An electrode group having a structure and a structure in which a nonaqueous electrolyte is accommodated may be used.

Next, the positive electrode 4, the separator 5, the negative electrode 6, and the non-aqueous electrolyte will be described in detail.

1) Positive electrode 4 The positive electrode contains at least a positive electrode active material, and is usually used by forming a positive electrode active material layer on one or both surfaces of a sheet-shaped current collector. For example, a positive electrode active material, a conductive agent, and a suspension in which a binder is appropriately suspended in a solvent may be applied to the surface of a current collector such as an aluminum foil, dried, and pressed to form a positive electrode active material layer.

The positive electrode active material can be used without any particular limitation as long as it can occlude the alkali metal during discharging of the battery and release the alkali metal during charging.

For example, as the positive electrode active material used in a lithium ion secondary battery using lithium as an alkali metal, various oxides and sulfides can be mentioned. For example, manganese dioxide (MnO ₂ ), lithium manganese composite oxide (eg, LiMn ₂ O ₄ or LiMnO ₂ ), lithium nickel composite oxide (eg, LiNiO ₂ ), lithium cobalt composite oxide (LiCoO ₂ ), lithium nickel cobalt composite Oxides (eg, LiNi _{1 -x} Co _x O ₂ ), lithium manganese cobalt composite oxides (eg, LiMn _x C
o _1-x O ₂ ) and vanadium oxide (eg, V ₂ O ₅ ). Further, organic materials such as a conductive polymer material and a disulfide-based polymer material can also be used. More preferable positive electrode active materials include lithium manganese composite oxide (LiMn ₂ O ₄ ), lithium nickel composite oxide (LiNiO ₂ ), and lithium cobalt composite oxide (Li
CoO ₂ ), lithium nickel cobalt composite oxide (Li
Ni _0.8 Co _0.2 O _2), lithium manganese cobalt composite oxides _{(LiMn x Co 1-x O} 2) , and the like.

The current collector can be used without any particular limitation as long as it is a conductive material. In particular, as the current collector for the positive electrode, it is preferable to use a material which is hardly oxidized during the battery reaction. , Stainless steel, titanium or the like may be used.

Examples of the conductive agent include acetylene black, carbon black, graphite and the like. Examples of the binder include polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVd).
F), fluorine-based rubber and the like. The compounding ratio of the positive electrode active material, the conductive agent and the binder is 80 to 9 for the positive electrode active material.
5% by weight, conductive agent 3-20% by weight, binder 2-7% by weight
It is preferable to be within the range.

2) Negative electrode 6 FIG. 2 is a sectional view showing an example of the negative electrode according to the present invention.

The negative electrode 6 according to the present invention comprises a current collector 21, a negative electrode active material layer 22 formed on the current collector surface and containing at least a negative electrode active material, and a carbon material formed on the negative electrode active material layer. And a covering layer 23 made of.

The current collector 21 can be used without particular limitation as long as it is a conductive material. In particular, as the current collector for the negative electrode, it is preferable to use a material that is difficult to dissolve during a battery reaction.
For example, sheet-like copper or nickel may be used.

The negative electrode active material layer 22 is formed by forming a single layer of the negative electrode active material or a mixture containing the negative electrode active material. The negative electrode active material is a metal material that can release an alkali metal when discharging the battery and occlude the alkali metal when charging. For example, in a lithium ion secondary battery using lithium as the alkali metal, for example, Sn-N
i-alloy, Sn-Ni-Cu alloy, Sn-Sb alloy, Cu
-Sn alloy, Sn-Sb-Cu-Al alloy, Mg-
Sn alloy, Mg-Sb alloy, Mg-Sb-Ni alloy,
Examples thereof include lithium alloys such as a Li-Al alloy, a Li-Pb alloy, and a Li-In alloy, and lithium metal. In particular, an alloy containing lithium can significantly improve charge / discharge efficiency. The preferred range is 0.02
wt% or more and 55 wt% or less, particularly preferably 0.05 w
t% or more and 45 wt% or less, more preferably 0.1 wt%
It is preferable to use an alloy containing at least 30 wt% of lithium.

The crystal structure of the negative electrode active material layer thus formed is not particularly limited, and may be a crystal phase, a microcrystal, or an amorphous phase. Further, when the negative electrode active material is an alloy, a single phase may be formed depending on the material system, an alloy composed of a plurality of phases may be used, or adjustment may be made as necessary. In addition, various impurities such as fluorine may be mixed into the negative electrode active material.
If it is below, the function as a negative electrode active material can usually be sufficiently exhibited.

The thickness of the negative electrode active material layer 22 is 0.01 to 5
The thickness is preferably 0 μm, more preferably 0.05 μm to 30 μm, and particularly preferably 0.1 μm to 15 μm. When the film thickness is smaller than the above range, the lithium ion occlusion amount of the negative electrode becomes small, so that the battery capacity becomes small. On the other hand, if it is larger than the above range, the negative electrode active material may be finely divided and may be separated from the negative electrode active material layer.

The negative electrode active material layer 22 is formed on the current collector surface by a known method, for example, a sintering method, a super-quenching method, a plating method, a sputtering method, a rolling method, a sol-gel method, a vapor deposition method, or the like. be able to.

For example, an alloy composed of a negative electrode active material adjusted to a predetermined composition ratio disposed on a current collector is moved at a moving speed of 5%.
By quenching by a super-quenching device using a single roll method or a twin roll method while moving in a range of ５０50 m / s, a layered quenched body made of a negative electrode active material can be formed on the surface of the current collector. In addition, the powder of each element constituting the negative electrode active material is pressure-formed integrally with the current collector, and then heat-treated in an inert gas atmosphere or under vacuum to form a negative electrode active material layer on the current collector surface. Can be formed.

Further, the negative electrode active material layer 22 formed by these methods may be further subjected to a heat treatment if necessary. This treatment temperature depends on the composition of the negative electrode active material layer 22, but is preferably performed in a temperature range of about 100C to 500C. Although the optimum heat treatment time varies depending on the heat treatment temperature, the optimum heat treatment time is about 0.1 mm.
1 to 500 hours, preferably 0.5 to 100 hours, more preferably 1 to 50 hours.

The coating layer 23 is formed on the negative electrode active material layer, suppresses a change in volume of the negative electrode active material layer, suppresses fine particles, and retains the fine particles on the current collector even when the fine particles are formed. Functions as a cover for By forming this coating layer, it is possible to suppress the volume expansion of the negative electrode active material layer, and it is possible to prevent micronization.

The coating layer 23 is formed of a carbon material conventionally used as a negative electrode active material, or a component such as the carbon material and a binder resin. Specific examples of the carbon material include graphite, acetylene black, and carbon black.

Since the coating layer 23 allows the passage of lithium ions, the coating layer 23 does not hinder the insertion and extraction of the lithium element into and from the positive electrode active material layer 22. In addition, as described above, since it also has a function as a negative electrode active material, the amount of lithium stored in the negative electrode can be increased as compared with the case where another material is used. Further, when a conductive agent is added to the coating layer 23, the current collection efficiency in the coating film can be improved.

The thickness of the coating layer 23 is 0.1 μm or more and 20 μm or more.
It is preferable that the thickness be 0 μm or less. If the thickness is less than 0.1 μm, it is difficult to form a uniform film,
If it exceeds 2,000, the permeability of lithium ions decreases. Also,
The ratio of the thickness of the negative electrode active material layer 22 to the thickness of the coating layer 23 is preferably 0.01 or more and 0.95 or less.
If it is smaller than 0.01, it is difficult to sufficiently suppress desorption in the negative electrode active material layer. is there.

For example, the coating layer 23 is formed as follows.

The coating layer 23 only needs to contain at least the negative electrode active material, but is composed of a carbon material, a binder, and if necessary, a conductive agent. The liquid is applied onto the current collector 21 via the negative electrode active material layer.
It is formed by dry pressing.

Examples of the binder include polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), fluorine rubber, ethylene-butadiene rubber (SBR), and carboxymethyl cellulose (CMC).
And the like.

As for the solvent used for forming the coating layer 22, when the anode active material layer 22 easily reacts with water, an appropriate organic solvent, for example, an N-methylpyrrolidone (NMP) solution is used. Is desirable. The compounding ratio of the negative electrode active material, the conductive agent and the binder is 70 to 9
It is preferable that the content is 5 wt%, the conductive agent is 0 to 25 wt%, and the binder is 2 to 10 wt%.

The negative electrode active material layer and the coating layer can be formed on one side or both sides of a sheet-like current collector.

3) Separator 5 The separator 5 is for holding the non-aqueous electrolyte according to the present invention and for insulating between the positive electrode and the negative electrode. The separator 5 is made of an insulating material and has a fine structure for connecting the positive electrode and the negative electrode. Any material having pores can be used without particular limitation, and specific examples thereof include a synthetic resin nonwoven fabric, a polyethylene porous film, and a polypropylene porous film.

4) Nonaqueous Electrolyte The nonaqueous electrolyte held by the separator 5 is a liquid electrolyte prepared by dissolving an electrolyte in a nonaqueous solvent, or a polymer material containing the nonaqueous solvent and the electrolyte in a polymer material. And a solid polymer electrolyte containing only the electrolyte, and an inorganic solid electrolyte having lithium ion conductivity.

As the liquid electrolyte, for example, a known nonaqueous solvent obtained by dissolving a lithium salt as an electrolyte in a nonaqueous solvent of a lithium battery can be used. Examples of such a liquid electrolyte include ethylene carbonate (EC) and propylene carbonate (PC). It is preferable to use a cyclic carbonate or a non-aqueous solvent mainly composed of a mixed solvent of a cyclic carbonate and a non-aqueous solvent having a lower viscosity than the cyclic carbonate (hereinafter, a second solvent).

Examples of the second solvent include chain carbonates such as dimethyl carbonate, methyl ethyl carbonate and diethyl carbonate, γ-butyrolactone,
Acetonitrile, methyl propionate, ethyl propionate, cyclic ethers such as tetrahydrofuran and 2-methyltetrahydrofuran, and chain ethers such as dimethoxyethane and diethoxyethane are exemplified.

Examples of the electrolyte include an alkali salt, and in particular, a lithium salt. As lithium salts, lithium hexafluorophosphate (LiPF ₆ ), lithium borofluoride (LiBF ₄ ), lithium arsenic hexafluoride (L
iAsF ₆ ), lithium perchlorate (LiClO ₄ ), lithium trifluorometasulfonate (LiCF ₃ SO ₃ ), and the like. In particular, lithium hexafluorophosphate (L
iPF ₆ ) and lithium borofluoride (LiBF ₄ ) are preferred. The amount of the electrolyte dissolved in the non-aqueous solvent is 0.1.
It is preferably from 5 to 2.0 mol / l.

The polymer gel electrolyte is obtained by dissolving the solvent and the electrolyte in a polymer material to form a gel. The polymer material may be polyacrylonitrile, polyacrylate, polyvinylidene fluoride (PVdF), polyethylene oxide (PECO). )) Or copolymers with other monomers.

The solid electrolyte is obtained by dissolving the above-mentioned electrolyte in a polymer material and solidifying it. Polymer materials include polyacrylonitrile, polyvinylidene fluoride (P
VdF), a polymer of a monomer such as polyethylene oxide (PEO), or a copolymer with another monomer. Examples of the inorganic solid electrolyte include ceramic materials containing lithium. Among them, Li ₃ N and Li ₃ P
O ₄ —Li ₂ S—SiS ₂ , LiI—Li ₂ S—SiS ₂ glass and the like can be mentioned.

Although an example in which the present invention is applied to a cylindrical non-aqueous electrolyte secondary battery has been described with reference to FIG. 1 described above, the present invention can be similarly applied to a rectangular non-aqueous electrolyte secondary battery. The electrode group housed in the battery container is not limited to a spiral shape, but may be a form in which a plurality of positive electrodes, separators, and negative electrodes are stacked in this order.

The non-aqueous electrolyte secondary battery according to the present invention is not limited to the above-described embodiment as long as it is within the scope of the present invention.

[0054]

EXAMPLE A non-aqueous electrolyte secondary battery as shown in FIG. 1 was prepared.

<Preparation of Positive Electrode> First, 91% by weight of lithium cobalt oxide (LiCoO ₂ ) powder as a positive electrode active material was mixed with 2.5% by weight of acetylene black, 3% by weight of graphite,
4% by weight of polyvinylidene fluoride (PVdF) and an N-methylpyrrolidone (NMP) solution were added and mixed.
A positive electrode having an electrode density of 3.0 g / cm ³ was prepared by applying the solution to a 5 μm aluminum foil current collector, drying and pressing.

<Preparation of Negative Electrode> First, an alloy thin film having a composition of 0.75Sn-0.25Ni was plated on a current collector made of a copper foil having a thickness of 12 μm as follows.
A negative electrode active material layer made of a -Ni alloy was formed.

The electrodeposition conditions at the time of plating were 45 g of tin chloride /
L, nickel chloride 10g / L, potassium pyrophosphate 20
0 g / L, glycine 20 g / L, ammonia water 5 ml /
An L pyrophosphate bath was prepared, the pH was 8, and the bath temperature was 50 ° C. Under the above conditions, a current density of 0.5 A / dm ^{2 and a} film thickness of 1
A negative electrode active material layer made of a μm alloy thin film was prepared.

Next, a coating layer was formed on the surface of the negative electrode active material layer.

First, mesophase pitch-based carbon fibers (M
CF) 85% by weight, 5% by weight of graphite, 3% by weight of acetylene black, 7% by weight of PVdF and an NMP solution were added and mixed, and 50 μm was added to the surface of the previously obtained negative electrode active material layer.
After coating, drying and pressing, a coating layer was formed to produce a negative electrode.

<Preparation of Electrode Group> A separator made of a polyethylene porous film was prepared, and the positive electrode and the negative electrode obtained above were laminated through the separator.
An electrode group was prepared by spirally winding the negative electrode so as to be located at the outermost periphery.

<Preparation of Nonaqueous Electrolyte> Further, lithium hexafluorophosphate (LiPF ₆ ) was added to a mixed solvent of ethylene carbonate (EC) and methyl ethyl carbonate (MEC) at a mixing volume ratio of 1: 2. The solution was dissolved at a concentration of 0.0 mol / L to prepare a non-aqueous electrolyte.

The obtained electrode group and the electrolytic solution were housed in stainless steel bottomed cylindrical containers, respectively, to assemble the above-mentioned cylindrical non-aqueous electrolyte secondary battery shown in FIG.

Comparative Example 1 For comparison, for the negative electrode, mesophase pitch-based carbon fibers (fiber diameter 7 μm, average fiber length 25 μm, average face spacing d () were heat-treated at 2900 ° C. without using an alloy as the negative electrode active material. A non-aqueous electrolyte secondary battery was assembled in the same manner as in Example 1 except that powder having a specific surface area of 2.5 m ² / g) measured by the BET method was used.

Comparative Example 2 A non-aqueous electrolyte secondary battery was prepared in the same manner as in Example 1 except that no coating layer was formed as a negative electrode.

Examples 2 to 10 Non-aqueous electrolyte secondary batteries were produced in the same manner as in Example 1 except that the alloy used for the negative electrode active material layer was changed to the alloy shown in Table 1.

<Evaluation of Battery> Each of the non-aqueous electrolyte secondary batteries obtained in Examples 1 to 10 and Comparative Examples 1 and 2 was evaluated as follows.

Each non-aqueous electrolyte secondary battery was charged at a charging current of 1 A to 4.2 V for 2.5 hours, and then charged at 5 A to 2.0 V.
, A charge / discharge cycle test was performed. From the results, it was found that the high-rate discharge capacity ratio and the capacity retention ratio (300% with respect to the discharge capacity in the first cycle) were obtained for each nonaqueous electrolyte secondary battery.
(The ratio of the discharge capacity at the cycle). The results are shown in Table 1 below. The high-rate discharge capacity ratio is a ratio when the high-rate discharge capacity of the carbonaceous material negative electrode of Comparative Example 1 is set to 1.

[Table 1] As is clear from Table 1, the non-aqueous electrolyte secondary batteries of Examples 1 to 10 of the present invention have a higher rate discharge capacity and a higher capacity retention at 300 cycles than the non-aqueous charge-loss secondary batteries of Comparative Example 2. It can be seen that the rate was dramatically improved and the cycle characteristics were excellent.

[0068]

As described in detail above, according to the present invention, a non-aqueous electrolyte secondary battery having a high rate discharge capacity and good cycle characteristics can be provided.

[Brief description of the drawings]

FIG. 1 is a partial cross-sectional view showing a non-aqueous electrolyte secondary battery according to the present invention.

FIG. 2 is a sectional view showing a negative electrode according to the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Container 3 ... Electrode group 4 ... Positive electrode 5 ... Separator 6 ... Negative electrode 11 ... Positive current collecting lead 13 ... Negative current collecting lead 21 ... Current collector 22 ... Negative electrode active material layer 23 ... Coating layer

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 5H029 AJ03 AJ05 AK03 AL06 AL11 AL12 AL18 AM03 AM04 AM05 AM07 BJ02 BJ13 BJ14 DJ12 HJ04 HJ12 5H050 AA07 AA08 BA16 BA17 CA08 CA09 CB09 CB11 CB29 EA02 FA04 HA04 HA12

Claims (4)

[Claims] 1. A positive electrode comprising at least a positive electrode active material; a current collector; a negative electrode active material layer having an alloy formed on the surface of the current collector for absorbing and releasing alkali metal; and formed on the negative electrode active material layer. A non-aqueous electrolyte secondary battery, comprising: a negative electrode including a coated layer made of a carbon material; and a non-aqueous electrolyte sandwiched between the positive electrode and the negative electrode. 2. The non-aqueous electrolyte secondary battery according to claim 1, wherein the thickness of the active material layer is 0.01 μm or more and 50 μm or less. 3. The coating layer has a thickness of 0.1 μm or more and 20 μm or more.
2. The non-aqueous electrolyte secondary battery according to claim 1, wherein the thickness is 0 μm or less. 4. The non-aqueous electrolyte secondary battery according to claim 1, wherein a thickness ratio of the negative electrode active material layer to a thickness of the coating layer is 0.01 or more and 0.95 or less.