JP2020004685A - All-solid battery - Google Patents

Abstract

To provide an all-solid battery which can achieve a satisfactory initial discharge capacity chiefly.SOLUTION: The disclosure hereof solves the above problem by providing an all-solid battery having a positive electrode layer, a negative electrode layer, and a solid electrolyte layer formed between the positive and negative electrode layers. In the all-solid battery, the positive electrode layer contains a positive electrode active substance having a composition represented by LiNiCoMnO(1.15≤x≤1.55, a+b+c=1, 0≤a≤0.85, 0≤b≤0.85, 0.15≤c≤0.70, and y is a value determined to meet the requirement of neutrality of electricity), and the negative electrode layer contains a Si-based active substance. The all-solid battery satisfies 2≤A≤5.5 where a capacity ratio of a negative electrode capacity to a positive electrode capacity is A. As to the positive electrode active substance, the all-solid battery satisfies 0.1083A+0.9085≤Li/Me where Li/Me represents a mole ratio of Li to Me (Me is a metal element other than Li).SELECTED DRAWING: Figure 2

Description

  The present disclosure relates to all solid state batteries.

  The all-solid-state battery has a solid electrolyte layer between the positive electrode layer and the negative electrode layer, and has an advantage that the safety device can be simplified more easily than a liquid battery having an electrolyte containing a flammable organic solvent. Having.

On the other hand, although not related to an all-solid-state battery, Patent Document 1 discloses a method for manufacturing a non-aqueous electrolyte secondary battery including an activation step of activating the non-aqueous electrolyte secondary battery by charging and discharging, The non-aqueous electrolyte secondary battery includes a solid solution positive electrode and a Si-based negative electrode, and the solid solution positive electrode includes [Li _1.5 ] [Li _{{0.5 (1-x)}} Mn _1-x M _1.5x A process in which the activation step switches the applied charging current value to a higher charging current value one or more times before reaching the maximum voltage during the initial charging, in which the active material represented by O ₃ is included. A method for manufacturing a non-aqueous electrolyte secondary battery, characterized in that the first switching of the charging current value is performed at a charging voltage of 3.75 V or more and 4.52 V or less.

JP 2018-055901 A JP 2013-243116 A

  There is a need for an all-solid-state battery having a good initial discharge capacity. The present disclosure has been made in view of the above circumstances, and has as its main object to provide an all-solid-state battery having a good initial discharge capacity.

In order to solve the above problems, the present disclosure relates to an all-solid battery including a positive electrode layer, a negative electrode layer, and a solid electrolyte layer formed between the positive electrode layer and the negative electrode layer, wherein the positive electrode layer _{is, Li x Ni a Co b Mn} c O y (1.15 ≦ x ≦ 1.55, a + b + c = 1,0 ≦ a ≦ 0.85,0 ≦ b ≦ 0.85,0.15 ≦ c ≦ 0 .70, y is a value determined so as to satisfy charge neutrality), the negative electrode layer contains a Si-based active material, and the negative electrode capacity with respect to the positive electrode capacity is included. When the capacity ratio is A, 2 ≦ A ≦ 5.5 is satisfied, and when the molar ratio of Li to Me (Me is a metal element other than Li) in the positive electrode active material is Li / Me, 0 is satisfied. .1083A + 0.9085 ≦ Li / Me is provided.

  According to the present disclosure, when the capacity ratio A and the molar ratio Li / Me satisfy a predetermined relationship, an all-solid-state battery having a good initial discharge capacity can be obtained.

  The all solid state battery according to the present disclosure has an effect that the initial discharge capacity is good.

1 is a schematic cross-sectional view illustrating an example of an all solid state battery according to the present disclosure. 4 is a graph showing a relationship between a Li / Me ratio and an initial discharge capacity. 4 is a graph showing a relationship between a capacity ratio A and a Li / Me ratio.

  Hereinafter, the all solid state battery according to the present disclosure will be described in detail.

  FIG. 1 is a schematic cross-sectional view illustrating an example of the all solid state battery according to the present disclosure. The all-solid-state battery 10 shown in FIG. 1 has a positive electrode layer 1, a negative electrode layer 2, and a solid electrolyte layer 3 formed between the positive electrode layer 1 and the negative electrode layer 2. Further, the all-solid-state battery 10 includes a positive electrode current collector 4 that collects the current of the positive electrode layer 1 and a negative electrode current collector 5 that collects the current of the negative electrode layer 2. The positive electrode layer 1 contains a positive electrode active material having a predetermined composition, and the negative electrode layer 2 contains a Si-based active material. When the capacity ratio of the negative electrode capacity to the positive electrode capacity is A, the capacity ratio A is within a predetermined range. In the positive electrode active material, when the molar ratio of Li to Me (Me is a metal element other than Li) is Li / Me, the capacity ratio A and Li / Me satisfy a predetermined relationship.

  According to the present disclosure, when the capacity ratio A and the molar ratio Li / Me satisfy a predetermined relationship, an all-solid-state battery having a good initial discharge capacity can be obtained. Here, the Si-based active material is known as a high-capacity negative electrode active material. However, since the volume change during charge / discharge is large, cracks occur in the negative electrode layer or the Si-based active material slides down from the negative electrode layer. Easy to do. On the other hand, by increasing the capacity ratio of the negative electrode capacity to the positive electrode capacity, the volume change of the entire negative electrode layer is reduced, cracks are generated in the negative electrode layer, or the Si-based active material slides down from the negative electrode layer. Can be suppressed.

  On the other hand, the Si-based active material reacts with Li at the time of the first charge, but Li may not be desorbed from the Si-based active material at the time of the first discharge and Li may be fixed (Li deactivation). In particular, when the capacity ratio A of the negative electrode capacity to the positive electrode capacity is increased, the influence of Li deactivation by the Si-based active material increases. On the other hand, if a positive electrode active material having a greater amount of Li than usual is used as the positive electrode active material, the actual capacity of the battery (capacity after the second cycle or later, even if Li deactivation occurs due to the Si-based active material) ) Can be improved. In the present disclosure, it has been found that a certain correlation is found between the capacity ratio A, the Li / Me ratio in the positive electrode active material, and the initial discharge capacity. Specifically, it has been found that by setting the Li / Me ratio to a predetermined value or more for a certain capacity ratio A, the maximum capacity can be drawn out as the initial discharge capacity. As described above, according to the present disclosure, when the capacity ratio A and the molar ratio Li / Me satisfy the predetermined relationship, an all-solid-state battery having a good initial discharge capacity can be obtained.

  The capacity ratio of the negative electrode capacity to the positive electrode capacity is defined as a capacity ratio A. The negative electrode capacity is obtained by multiplying the theoretical capacity of the negative electrode active material by the amount of the negative electrode active material. On the other hand, the positive electrode capacity is obtained by multiplying the charge capacity of the positive electrode active material by the amount of the positive electrode active material. The charge capacity of the positive electrode active material was determined by preparing a monopolar compact cell using metal Li as the counter electrode, performing CCCV charge at 0.1 C (1/100 C cut or 20 hours cut), and calculating the obtained initial charge capacity by the positive electrode. The charge capacity of the active material. The capacity ratio A is, for example, 2 or more, and may be 2.5 or more. On the other hand, the capacity ratio A is, for example, 5.5 or less, and may be 5.0 or less.

  In the positive electrode active material, the molar ratio of Li to Me (Me is a metal element other than Li) is defined as Li / Me. The molar ratio Li / Me may be referred to as a Li / Me ratio. The all solid state battery in the present disclosure generally satisfies 0.1083A + 0.9085 ≦ Li / Me.

1. Positive electrode layer The positive electrode layer is a layer containing at least a positive electrode active material. Further, the positive electrode layer may contain at least one of a solid electrolyte, a conductive material, and a binder, if necessary.

Positive electrode layer, as a cathode active _{material, Li x Ni a Co b Mn} c O y (1.15 ≦ x ≦ 1.55, a + b + c = 1,0 ≦ a ≦ 0.85,0 ≦ b ≦ 0.85, 0.15 ≦ c ≦ 0.70, y is a value determined so as to satisfy the charge neutrality). Hereinafter, this positive electrode active material may be referred to as an NCM active material. The NCM active material may further contain a small amount of a metal element. Examples of the small amount of metal element include an Al element, a W element, and a Zr element. The ratio of the small amount of the metal element is, for example, 10 mol% or less, and may be 5 mol% or less with respect to all the metal elements contained in the NCM active material.

  X is, for example, 1.15 or more, and may be 1.20 or more. On the other hand, the x is, for example, 1.55 or less, and may be 1.50 or less. The y is a value determined so as to satisfy the charge neutrality, and varies depending on the composition of the NCM active material. The y is greater than 2, for example. On the other hand, the above y is, for example, 3 or less.

  The above a may be 0 or may be larger than 0. In the latter case, the value a is, for example, 0.10 or more, and may be 0.15 or more. On the other hand, the value a is, for example, 0.85 or less, may be 0.70 or less, or may be 0.50 or less. The above b may be 0 or may be larger than 0. In the latter case, b is, for example, 0.10 or more, and may be 0.15 or more. On the other hand, b is, for example, 0.85 or less, may be 0.70 or less, or may be 0.50 or less. The above c is, for example, 0.15 or more, may be 0.20 or more, or may be 0.25 or more. On the other hand, c is, for example, 0.70 or less, may be 0.60 or less, or may be 0.50 or less.

  In the NCM active material, the molar ratio of Li to Me (Me is a metal element other than Li) is defined as Li / Me. The value of Li / Me is, for example, 1.15 or more, and may be 1.20 or more. If the value of Li / Me is too small, the initial discharge capacity may not be sufficiently improved. On the other hand, the value of Li / Me is, for example, 1.55 or less, and may be 1.50 or less. If the value of Li / Me is too large, when Li desorbs from the NCM active material during the first charge, an irreversible structural change (for example, oxygen desorption) occurs in the NCM active material, and Li that can react during the first discharge is generated. The amount may decrease.

  The positive electrode layer may contain only the NCM active material as the positive electrode active material, or may contain another active material. In the latter case, the proportion of the NCM active material in all the positive electrode active materials may be 50% by weight or more, 70% by weight or more, or 90% by weight or more.

Further, the surface of the positive electrode active material may be covered with a coat layer. The reaction between the positive electrode active material and the solid electrolyte (particularly, a sulfide solid electrolyte) can be suppressed by the coat layer. Examples of the coat layer include Li-containing oxides such as LiNbO ₃ , Li ₃ PO ₄ , and LiPON. The thickness of the coat layer is, for example, 1 nm or more. On the other hand, the thickness of the coat layer is, for example, 20 nm or less, and may be 10 nm or less.

Examples of the shape of the positive electrode active material include a particle shape. The average particle diameter (D ₅₀ ) of the positive electrode active material is, for example, 0.1 μm or more and 50 μm or less. The average particle size can be calculated, for example, from measurement using a laser diffraction particle size distribution meter or a scanning electron microscope (SEM).

  The ratio of the positive electrode active material in the positive electrode layer is, for example, 20% by weight or more, may be 30% by weight or more, or may be 40% by weight or more. On the other hand, the ratio of the positive electrode active material in the positive electrode layer is 95% by weight or less, may be 90% by weight or less, or may be 80% by weight or less.

Further, the positive electrode layer may contain at least one of a solid electrolyte, a conductive material, and a binder, if necessary. Examples of the solid electrolyte include inorganic solid electrolytes such as a sulfide solid electrolyte, an oxide solid electrolyte, a nitride solid electrolyte, and a halide solid electrolyte. Examples of the sulfide solid electrolyte include a solid electrolyte containing a Li element, an X element (X is at least one of P, Si, Ge, Sn, B, Al, Ga, and In), and an S element. No. Further, the sulfide solid electrolyte may further contain at least one of an O element and a halogen element. Examples of the oxide solid electrolyte include a Li element, a Y element (Y is at least one of Nb, B, Al, Si, P, Ti, Zr, Mo, W, and S) and an O element. And a solid electrolyte containing the same. Examples of the nitride solid electrolyte include Li ₃ N, and examples of the halide solid electrolyte include LiCl, LiI, and LiBr.

  Examples of the conductive material include a carbon material. Examples of the carbon material include a particulate carbon material such as acetylene black (AB) and Ketjen black (KB), and a fibrous carbon material such as carbon fiber, carbon nanotube (CNT), and carbon nanofiber (CNF). .

  Examples of the binder include a rubber-based binder such as butylene rubber (BR) and styrene-butadiene rubber (SBR), and a fluoride-based binder such as polyvinylidene fluoride (PVDF).

  The thickness of the positive electrode layer is, for example, 0.1 μm or more and 1000 μm or less. Examples of the method for forming the positive electrode layer include a method of applying a slurry containing at least a positive electrode active material and a dispersion medium and drying the slurry.

2. Negative electrode layer The negative electrode layer is a layer containing at least a negative electrode active material. Further, the negative electrode layer may contain at least one of a solid electrolyte, a conductive material, and a binder, if necessary.

  The negative electrode layer contains a Si-based active material as a negative electrode active material. The Si-based active material is preferably an active material that can be alloyed with Li. Examples of the Si-based active material include simple Si, a Si alloy, and a Si oxide. The Si alloy preferably contains a Si element as a main component. The ratio of the Si element in the Si alloy may be, for example, 50 mol% or more, 70 mol% or more, or 90 mol% or more. An example of the Si oxide is SiO.

  The negative electrode layer may contain only the Si-based active material as the negative electrode active material, or may contain another active material. In the latter case, the proportion of the Si-based active material in all the negative electrode active materials may be 50% by weight or more, 70% by weight or more, or 90% by weight or more.

Examples of the shape of the negative electrode active material include a particle shape. The average particle size (D ₅₀ ) of the negative electrode active material is not particularly limited, but is, for example, 10 nm or more, and may be 100 nm or more. On the other hand, the average particle size (D ₅₀ ) of the negative electrode active material is, for example, 50 μm or less, and may be 20 μm or less.

  The ratio of the negative electrode active material in the negative electrode layer is, for example, 20% by weight or more, 30% by weight or more, or 40% by weight or more. On the other hand, the ratio of the negative electrode active material is, for example, 80% by weight or less, 70% by weight or less, or 60% by weight or less.

  The solid electrolyte, conductive material, and binder used for the negative electrode layer are the same as those described in the above “1. Positive electrode layer”, and thus description thereof is omitted here.

  The thickness of the negative electrode layer is, for example, 0.1 μm or more and 1000 μm or less. Examples of the method for forming the negative electrode layer include a method of applying a slurry containing at least a negative electrode active material and a dispersion medium and drying the slurry.

3. Solid electrolyte layer The solid electrolyte layer is a layer disposed between the positive electrode layer and the negative electrode layer. The solid electrolyte layer contains at least a solid electrolyte, and may contain a binder if necessary. The solid electrolyte, the binder, and the Li ion conductive material are the same as those described in the above “1. Positive electrode layer”, and thus description thereof will be omitted. Above all, the solid electrolyte layer preferably contains a sulfide solid electrolyte as the solid electrolyte.

  The thickness of the solid electrolyte layer is, for example, 0.1 μm or more and 1000 μm or less. As a method of forming the solid electrolyte layer, for example, a method of compression-molding a solid electrolyte can be mentioned.

4. Other Members The all-solid-state battery in the present disclosure has at least the negative electrode layer, the positive electrode layer, and the solid electrolyte layer described above. Further usually, it has a positive electrode current collector for collecting current of the positive electrode layer and a negative electrode current collector for collecting current of the negative electrode layer. Examples of the material of the positive electrode current collector include SUS, aluminum, nickel, iron, titanium, and carbon. On the other hand, examples of the material of the negative electrode current collector include SUS, copper, nickel, and carbon. Note that the thickness and shape of the positive electrode current collector and the negative electrode current collector are preferably appropriately selected depending on the use of the battery. In addition, the all-solid-state battery according to the present disclosure may include a battery case that houses the above-described negative electrode layer, positive electrode layer, and solid electrolyte layer.

5. All-solid-state battery The all-solid-state battery in the present disclosure is preferably an all-solid-state lithium battery. Further, the all-solid-state battery in the present disclosure may be a primary battery or a secondary battery, but is preferably a secondary battery. This is because it can be repeatedly charged and discharged and is useful, for example, as a vehicle-mounted battery. Further, the all-solid-state battery in the present disclosure may be a single-layer battery or a stacked battery. The stacked battery may be a monopolar stacked battery (a parallel-connected stacked battery) or a bipolar stacked battery (a series-connected stacked battery). Examples of the shape of the all solid state battery include a coin type, a laminate type, a cylindrical type, and a square type.

  Note that the present disclosure is not limited to the above embodiment. The above-described embodiment is an exemplification, and has substantially the same configuration as the technical idea described in the claims of the present disclosure, and any device having the same function and effect can be realized by the present invention. It is within the technical scope of the disclosure.

[Production example]
(1-z) A positive electrode active material having a composition represented by LiNi _0.33 Co _0.33 Mn _0.33 O ₂ -zLi ₂ MnO ₃ was produced. Specifically, lithium hydroxide, manganese carbonate, cobalt hydroxide, and nickel hydroxide are weighed so as to have a predetermined molar ratio, then mixed, and fired at 800 ° C. for 10 hours in an oxygen stream. To synthesize lithium nickel cobalt manganese oxide. Thus, z = 0, 0.05, 0.10, 0.15, 0.20, 0.25, 0.30, 0.35, 0.40, 0.45, 0.50, 0 .55 were produced.

[Comparative Example 1]
(Preparation of positive electrode structure)
A positive electrode active material (LiNi _1/3 Co _1/3 Mn _1/3 O ₂ , z = 0) and a sulfide solid electrolyte (LiI-Li ₂ O-Li ₂ SP ₂ S ₅ ) were added to the positive electrode active material: The sulfide solid electrolyte was weighed at a weight ratio of 75:25. Thereafter, with respect to 100 parts by weight of the positive electrode active material, 1.5 parts by weight of the PVDF-HFP binder (Soref 21510 manufactured by Solvay) and 3.0 parts by weight of the conductive material (VGCF, manufactured by Showa Denko KK) were used. Weighed. These materials were mixed, butyl butyrate was added, and the solid content was adjusted to 63% by weight. Thereafter, the mixture was kneaded for 1 minute using an ultrasonic homogenizer to obtain a positive electrode slurry. The obtained positive electrode slurry was applied to the surface of a positive electrode current collector (Al foil, manufactured by Showa Denko KK) using an applicator (350 μm), air-dried for 5 minutes, and heated and dried at 100 ° C. for 5 minutes. . Thereafter, roll pressing was performed at 25 ° C. and a linear pressure of 1 ton / cm to obtain a positive electrode structure having a positive electrode current collector and a positive electrode layer.

(Preparation of negative electrode structure)
Negative electrode active material (Si) and the sulfide solid electrolyte _{(LiI-Li 2 O-Li} 2 S-P 2 S 5), the negative electrode active material: and weighed 42 weight ratio of: sulfide solid electrolyte = 58. Thereafter, a binder solution having a concentration of 5% by weight (a butyl butyrate solution containing a PVDF-based binder manufactured by Kureha Corporation) was weighed to 1.5 parts by weight based on 100 parts by weight of the negative electrode active material. Further, the conductive material (VGCF) was weighed so as to be 3.0 parts by weight with respect to 100 parts by weight of the negative electrode active material. These materials were mixed, butyl butyrate was added, and the solid content was adjusted to 63% by weight. Thereafter, the mixture was kneaded for 1 minute using an ultrasonic homogenizer to obtain a negative electrode slurry. The obtained negative electrode slurry was applied to the surface of a negative electrode current collector (Cu foil) using an applicator, air-dried for 5 minutes, and heated and dried at 100 ° C. for 5 minutes. Thereafter, roll pressing was performed at 25 ° C. and a linear pressure of 1 ton / cm to obtain a negative electrode structure having a negative electrode current collector and a negative electrode layer.

  The capacity ratio of the negative electrode capacity to the positive electrode capacity was changed by adjusting the gap of the applicator (250 μm to 800 μm) at the time of coating the negative electrode slurry. In addition, the capacity ratio A is defined by the capacity ratio A = (theoretical capacity of the negative electrode active material × the amount of the negative electrode active material) / (the charge capacity of the positive electrode active material × the amount of the positive electrode active material). The capacity ratios were 2.0, 2.5, 3.0, 3.5, 4.0, 4.5, 5.0, and 5.5, respectively. Note that the charge capacity of the positive electrode active material corresponds to a 4.7 V charge capacity.

(Production of battery)
The battery was obtained by arranging the positive electrode layer of the positive electrode structure and the negative electrode layer of the negative electrode structure so as to face each other with the solid electrolyte layer interposed therebetween, and pressing at 5 tons.

[Comparative Examples 2, 3 and Examples 1 to 9]
A battery was obtained in the same manner as in Comparative Example 1, except that the composition of the positive electrode active material was changed to the content described in Table 1.

[Evaluation]
CCCV charging / discharging was performed on the batteries obtained in Comparative Examples 1 to 3 and Examples 1 to 9 under the conditions of an upper limit of 4.55 V, a lower limit of 2.5 V, and 0.1 C. The results of the initial discharge capacity [mAh / g] are shown in Tables 2 and 3 and FIG.

  As shown in Table 2, Table 3, and FIG. 2, there was a certain correlation between the capacity ratio A, the Li / Me ratio, and the initial discharge capacity. For example, when the capacity ratio A is 2.0, the initial discharge capacity increases as the Li / Me ratio increases. When the Li / Me ratio becomes 1.15 or more, the initial discharge capacity becomes substantially constant. became. This tendency was the same even when the capacity ratio A was other than 2.0. In other words, it has been confirmed that by setting the Li / Me ratio to a predetermined value or more for a certain capacity ratio A, the maximum capacity can be obtained as the initial discharge capacity.

  In addition, a state in which the initial discharge capacity becomes substantially constant is regarded as saturation, and a condition under which saturation occurs is determined. Based on Table 2 and FIG. 2, the range of the Li / Me ratio in which the saturation occurred was 1.15 or more when the capacity ratio A was 2.0, and 1. 20 or more, when the capacity ratio A is 3.0, it is 1.25 or more, when the capacity ratio A is 3.5, it is 1.30 or more, and when the capacity ratio A is 4.0, 1 0.35 or more, when the capacity ratio A is 4.5, it is 1.40 or more, when the capacity ratio A is 5.0, it is 1.45 or more, and when the capacity ratio A is 5.5, It was 1.55 or more.

  FIG. 3 shows these relationships. In FIG. 3, when the minimum Li / Me ratio at the capacity ratio A (for example, when the capacity ratio A is 2.0 and the Li / Me ratio is 1.20) is set to the minimum Li / Me ratio, FIG. , There are eight plots of the minimum Li / Me ratio. When a linear approximation is performed from these plots, the slope is 0.1083. When the Li / Me ratio is 5.5, there is a possibility that the Li / Me ratio is too large and the reliability is low. Therefore, the plot of the Li / Me ratio of 5.0 (5.0, 1.45) is used. ) Is defined as Y = 0.1083X + 0.9085. Thus, by setting the capacity ratio A and the Li / Me ratio so as to satisfy 0.1083A + 0.9085 ≦ Li / Me, it was confirmed that the maximum discharge capacity can be obtained as the initial discharge capacity. .

  The relational expression obtained from the plot of the minimum Li / Me ratio at eight points is Y = 0.1083X + 0.925. In this case, the all solid state battery in the present disclosure may satisfy 0.1083A + 0.925 ≦ Li / Me. Further, the relational expression obtained from the plot of the minimum Li / Me ratio at seven points in the range where the capacity ratio A is 2.0 to 5.0 is Y = 0.1X + 0.95. In this case, the all solid state battery according to the present disclosure may satisfy 0.1A + 0.95 ≦ Li / Me.

DESCRIPTION OF SYMBOLS 1 ... Positive electrode layer 2 ... Negative electrode layer 3 ... Solid electrolyte layer 4 ... Positive electrode current collector 5 ... Negative electrode current collector 10 ... All solid state battery

Claims (1)

A positive electrode layer, a negative electrode layer, an all-solid battery having a solid electrolyte layer formed between the positive electrode layer and the negative electrode layer,
The positive electrode _{layer, Li x Ni a Co b Mn} c O y (1.15 ≦ x ≦ 1.55, a + b + c = 1,0 ≦ a ≦ 0.85,0 ≦ b ≦ 0.85,0.15 ≦ c ≦ 0.70, y is a value determined so as to satisfy the charge neutrality).
The negative electrode layer contains a Si-based active material,
When the capacity ratio of the negative electrode capacity to the positive electrode capacity is A, 2 ≦ A ≦ 5.5 is satisfied;
An all-solid-state battery, which satisfies 0.1083A + 0.9085 ≦ Li / Me when a molar ratio of Li to Me (Me is a metal element other than Li) in the positive electrode active material is Li / Me.

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