Composite cathode for all-solid-state secondary battery

Abstract

The present invention provides a composite cathode for an all-solid-state secondary battery, characterized by comprising a cathode active material and a composite electrolyte comprising a sulfide-based solid electrolyte and a transition metal-containing chloride-based solid electrolyte. By providing stable and excellent electron / ion transfer pathways at high voltage, the composite cathode is capable of improving the lifespan and charge / discharge characteristics of the all-solid-state secondary battery.

Description

Composite anode for all-solid-state secondary batteries

[0001] The present invention relates to a composite anode for an all-solid-state secondary battery, and more particularly, to a composite anode for an all-solid-state secondary battery characterized by including a cathode active material and a composite electrolyte of a sulfide-based solid electrolyte and a transition metal-containing chloride-based solid electrolyte.

[0002] Lithium secondary batteries are widely used due to their excellent energy density and output characteristics, and secondary batteries containing liquid organic solvent-based electrolytes are commercialized.

[0003] However, secondary batteries based on liquid organic solvents are being criticized for the risk of explosion due to the decomposition of the liquid electrolyte by electrode reaction, which causes the battery to expand, and for the risk of fire due to leakage of the liquid electrolyte.

[0004] To address these issues, all-solid-state secondary batteries based on solid electrolytes have been developed. Representative solid electrolytes include oxide-based solid electrolytes, sulfide-based solid electrolytes, and hybrid solid electrolytes, with sulfide-based solid electrolytes being the most widely used.

[0005] However, conventional all-solid-state secondary batteries based on sulfide-based solid electrolytes have the disadvantages of generating a space charge layer, which is a depletion region, when the electrode and electrolyte come into contact with each other, and low oxidation stability (<3 V).

[0006] The above space charge layer is an electron-deficient layer, and since electron concentration occurs at the interface between the solid electrolyte and the positive electrode active material, it is a region where conductivity in a specific area does not exist, and therefore, its occurrence should be suppressed if possible.

[0007] In addition, the oxidation range of all-solid-state secondary batteries based on sulfide-based solid electrolytes is generally low, at around 2.5 to 2.6 V, which negatively affects the battery life.

[0008] Therefore, to overcome these problems, various studies are being conducted to further improve capacity / output / efficiency, etc. by coating the positive electrode active material with a material with high oxidation stability (>4.5 V). However, in terms of the actual manufacturing process, there is a disadvantage in that the process cost increases because the coating process is added.

[0009] Therefore, there is a high need in the industry to develop new technologies to solve these problems at once.

[0010] The present invention aims to solve the problems of the prior art as described above and the technical tasks requested from the past.

[0011] The inventors of the present invention, after repeated in-depth research and various experiments, developed a composite electrolyte composed of a sulfide-based solid electrolyte and a transition metal-containing chloride-based solid electrolyte, and confirmed that when a positive electrode is formed with this composite electrolyte, it can provide a stable and excellent electron / ion transfer path at high voltage, thereby improving the lifespan and charge / discharge characteristics of an all-solid-state secondary battery, thereby completing the present invention.

[0012] Therefore, the composite anode for an all-solid-state secondary battery according to the present invention is

[0013] positive electrode active material; and

[0014] Composite electrolyte of a sulfide-based solid electrolyte and a transition metal-containing halide-based solid electrolyte;

[0015] It consists of including.

[0016]

[0017] As explained above, when only a sulfide-based solid electrolyte is used for the positive electrode, there are problems such as space charge generation and low oxidation stability, which reduces the battery life. However, as in the present invention, when a chloride-based solid electrolyte containing a transition metal having excellent high-voltage stability is used together with a sulfide-based solid electrolyte to form a composite electrolyte, damage to the solid electrolyte on the surface of the conductive material included in the positive electrode can be prevented, a stable electron / ion transfer path can be supplied, thereby improving the lifespan and charge / discharge characteristics of the all-solid-state secondary battery, and minimizing side reactions at the positive electrode / solid electrolyte interface.

[0018] Specifically, although the sulfide-based solid electrolyte has high ionic conductivity, its oxidation range is low at approximately 2.54 to 2.6 V, which negatively affects its lifespan. On the other hand, the transition metal-containing chloride-based solid electrolyte of the present invention has high oxidation stability and thus high voltage stability, but has the disadvantages of high resistance and low ionic conductivity. Therefore, by forming a composite electrolyte with the sulfide-based solid electrolyte and the chloride-based solid electrolyte, the advantages of each solid electrolyte can be realized while compensating for the disadvantages of each solid electrolyte. In particular, the high compatibility of the transition metal-containing chloride-based solid electrolyte with the sulfide-based solid electrolyte enables the implementation of a low resistance value.

[0019]

[0020] In one specific example, the sulfide-based solid electrolyte may include a solid electrolyte represented by chemical formula 1.

[0021] Li a P b S c Z d (1)

[0022] In the above formula,

[0023] 0 <a≤20, 0<b≤6, 0<c≤20, 0≤d≤8;

[0024] Z is at least one selected from the group consisting of F, Cl, Br, I, and O.

[0025] A representative example of such sulfide-based solid electrolyte is Li6PS5Cl, which is known in the art.

[0026] Additionally, the chloride-based solid electrolyte may include, for example, lithium zirconium vanadium chloride (LZVC) represented by chemical formula 2.

[0027] Li e Zr f V g Cl h (2)

[0028] In the above formula,

[0029] 0 <e≤5, 0<f≤1, 0<g≤1, 0<h≤8.

[0030] The above lithium zirconium vanadium chloride (LZVC) is a chloride-based solid electrolyte containing two transition metals, Zr (zirconium) and V (vanadium), and as can be confirmed in the experimental contents described below, it can be synthesized by high-energy milling of a mixture of lithium chloride, zirconium chloride, and vanadium chloride.

[0031] In one preferred example, the lithium zirconium vanadium chloride (LZVC) may be Li5ZrVCl.

[0032] The voltage range at which the oxidation peak of the above chloride-based solid electrolyte occurs may preferably be 3.5 to 3.8 V.

[0033] A typical chloride-based solid electrolyte has a high oxidation range of 4.5 V or more, so it has low ionic conductivity and has low compatibility with sulfide-based solid electrolytes, resulting in high resistance. However, the transition metal-containing chloride-based solid electrolyte according to the present invention has a specific oxidation range as described above, so it has high compatibility with sulfide-based solid electrolytes, improved life characteristics, and relatively good ionic conductivity.

[0034]

[0035] In one specific example, when the weight fraction of the sulfide-based solid electrolyte in the composite anode is defined as A wt% and the weight fraction of the chloride-based solid electrolyte is defined as B wt%, B / A may be in the range of 1 to 4.

[0036] If B / A is lower than the above range, the life characteristics deteriorate, and conversely, if it is higher than the above range, the resistance increases and the ionic conductivity decreases, which is not desirable.

[0037] Therefore, when the content ratio (by weight) of the chloride-based solid electrolyte is at least the same as or up to four times higher than that of the sulfide-based solid electrolyte, excellent rate characteristics, life characteristics, etc. can be exhibited based on sufficiently high oxidation stability, and this can also be confirmed in the experimental results thereafter.

[0038] Within the range satisfying the above conditions, the weight fraction of the sulfide-based solid electrolyte may be, for example, in the range of 5 to 12.5 wt%, and the weight fraction of the chloride-based solid electrolyte may be in the range of 12.5 to 20 wt%.

[0039]

[0040] In one specific example, the sulfide-based solid electrolyte and the chloride-based solid electrolyte may have a voltage difference at which an oxidation peak occurs in a range of 0.7 to 0.9 V.

[0041] In addition, the oxidation current occurring at the oxidation peak of the above sulfide-based solid electrolyte is A mA / cm 2 The oxidation current occurring at the oxidation peak of the chloride-based solid electrolyte is B mA / cm. 2 When defined as , it can be in the range of 15<A / B<19.

[0042] If the oxidation range appears at a voltage range that is too small, the life characteristics will deteriorate due to frequent changes in the electrolyte during charge / discharge. The higher the oxidation range, the more stable the charge / discharge can be up to that voltage range. On the other hand, if the oxidation range appears at a voltage range that is too high, there is a problem of reduced ionic conductivity, which is not desirable.

[0043] Based on this, if the voltage / current difference of the oxidation reaction is too small, the effect of oxidation stability does not appear, and thus the meaning of forming a composite electrolyte is lost. Conversely, if the voltage / current difference of the oxidation reaction is too large, the compatibility between solid electrolytes is poor, the resistance is high, and ion transfer is not smooth, which is not desirable.

[0044]

[0045] The present invention also provides an all-solid-state secondary battery based on the composite anode described above, the all-solid-state secondary battery comprising the composite anode, the cathode, and an electrolyte layer disposed between the composite anode and the cathode.

[0046] In one preferred example, the electrolyte layer may be composed of a transition metal-containing chloride-based solid electrolyte.

[0047] As can be confirmed from the experimental results below, this electrolyte layer has better rate characteristics, life characteristics, etc. compared to the electrolyte layer using the conventional sulfide-based solid electrolyte. Specifically, the initial charge / discharge efficiency is better with the sulfide-based solid electrolyte, but when the charge / discharge cycle is repeated, the efficiency is better when the chloride-based solid electrolyte is applied. This is presumed to be because the life characteristics are good even after repeated charge / discharge cycles based on the high oxidation stability.

[0048] Since other configurations and manufacturing methods of all-solid-state secondary batteries are known in the art, detailed descriptions thereof are omitted in this specification.

[0049] As described above, the composite cathode for an all-solid-state secondary battery according to the present invention can provide a stable and excellent electron / ion transfer path at high voltage by using a composite electrolyte of a sulfide-based solid electrolyte and a transition metal-containing chloride-based solid electrolyte, thereby improving the lifespan and charge / discharge characteristics of the all-solid-state secondary battery.

[0050] Figure 1 is a graph showing the change in current density versus voltage of Li6PS5Cl, a solid electrolyte, in Experimental Example 1, showing the oxidation peak;

[0051] Figure 2 is a graph of the oxidation peak of the change in current density versus voltage of Li5ZrVCl, a solid electrolyte, in Experimental Example 1.

[0052] Hereinafter, the present invention will be described in more detail with reference to embodiments of the present invention, but the scope of the present invention is not limited thereto.

[0053]

[0054] Comparative Example 1

[0055] Caustic soda and ammonia were added to a 500 L cylindrical reactor to adjust the initial pH to 11.5 to 12.0, and then a metal salt aqueous solution with a ratio of Ni:Co:Mn of 90:06:04 was continuously supplied together with the caustic soda and ammonia aqueous solutions to proceed with the reaction. The pH of the composite in the reactor was adjusted to 11.5 to 12.0, and the ammonia concentration in the reactor was adjusted to 6000 to 8000 ppm. A stirring speed of 420 rpm was applied to synthesize a transition metal precursor by co-precipitation reaction at 60°C for 34 hours.

[0056] When the precursor manufactured above and LiOH were mixed at a Li / Me=1.01 ratio, 1.5% WO3 was added by weight, and the mixture was mixed in a 10L mixer (Nippon Coke & Engineering) under the set conditions of 100 rpm / 1 min → 400 rpm / 5 min → 500 rpm / 15 min. Then, the mixture was calcined at 700°C for 30 hours to manufacture a cathode active material.

[0057] In addition, LiCl (lithium chloride), ZrCl4 (zirconium (IV) chloride), and VCl2 (vanadium (II) chloride) were mixed in a weight ratio of 11.4:2.3:2.6, placed in a ball mill jar with zirconia balls, and subjected to high-energy milling (15 min run, 15 min rest) at 500 rpm for 12 hours in a ball milling device to synthesize Li5ZrVCl.

[0058] A composite cathode material was manufactured by uniformly mixing 70 wt% of the cathode active material manufactured above, 5 wt% of carbon black (Super-P) as a conductive material, and 25 wt% of Li5ZrVCl synthesized above.

[0059] A commercially available Li6PS5Cl was pressurized to 17 MPa in an all-solid-state battery cell to form an SE layer (solid electrolyte layer), the composite cathode material was applied to one surface of the SE layer, and then a counter electrode (Li foil, In foil) was added to the other surface of the SE layer to manufacture an electrode assembly, which was then compressed to 42 MPa to manufacture an all-solid-state secondary battery.

[0060]

[0061] Example 1

[0062] An all-solid-state secondary battery was manufactured in the same manner as in Comparative Example 1, except that a mixture of 5 wt% Li6PS5Cl and 20 wt% Li5ZrVCl was used instead of 25 wt% Li5ZrVCl when manufacturing the composite cathode material.

[0063]

[0064] Example 2

[0065] An all-solid-state secondary battery was manufactured in the same manner as in Comparative Example 1, except that a mixture of 10 wt% Li6PS5Cl and 15 wt% Li5ZrVCl was used instead of 25 wt% Li5ZrVCl when manufacturing the composite cathode material.

[0066]

[0067] Example 3

[0068] An all-solid-state secondary battery was manufactured in the same manner as in Comparative Example 1, except that a mixture of 12.5 wt% Li6PS5Cl and 12.5 wt% Li5ZrVCl was used instead of 25 wt% Li5ZrVCl when manufacturing the composite cathode material.

[0069]

[0070] Comparative Example 2

[0071] An all-solid-state secondary battery was manufactured in the same manner as in Comparative Example 1, except that a mixture of 15 wt% Li6PS5Cl and 10 wt% Li5ZrVCl was used instead of 25 wt% Li5ZrVCl when manufacturing the composite cathode material.

[0072]

[0073] Comparative Example 3

[0074] An all-solid-state secondary battery was manufactured in the same manner as in Comparative Example 1, except that a mixture of 20 wt% Li6PS5Cl and 5 wt% Li5ZrVCl was used instead of 25 wt% Li5ZrVCl when manufacturing the composite cathode material.

[0075]

[0076] Comparative Example 4

[0077] An all-solid-state secondary battery was manufactured in the same manner as in Comparative Example 1, except that 25 wt% of Li6PS5Cl was used instead of 25 wt% of Li5ZrVCl when manufacturing the composite cathode material.

[0078]

[0079] Comparative Example 5

[0080] An all-solid-state secondary battery was manufactured in the same manner as in Comparative Example 1, except that 25 wt% of Li3YBr6, synthesized by high-energy milling of raw materials as described above, was used instead of 25 wt% of Li5ZrVCl in the manufacture of the composite cathode material.

[0081]

[0082] Comparative Example 6

[0083] An all-solid-state secondary battery was manufactured in the same manner as in Comparative Example 1, except that 25 wt% of Li3ZrCl5O synthesized by high-energy milling of raw materials as described above was used instead of 25 wt% of Li5ZrVCl when manufacturing the composite cathode material.

[0084]

[0085] Comparative Example 7

[0086] An all-solid-state secondary battery was manufactured in the same manner as in Comparative Example 1, except that instead of 25 wt% Li5ZrVCl in the manufacture of the composite cathode material, a mixture of 5 wt% Li6PS5Cl and 20 wt% Li3YBr6 synthesized by high-energy milling of raw materials as described above was used.

[0087]

[0088] Comparative Example 8

[0089] An all-solid-state secondary battery was manufactured in the same manner as in Comparative Example 1, except that instead of 25 wt% Li5ZrVCl in the manufacture of the composite cathode material, a mixture of 5 wt% Li6PS5Cl and 20 wt% Li3ZrCl5O synthesized by high-energy milling of raw materials as described above was used.

[0090]

[0091] Example 4

[0092] An all-solid-state secondary battery was manufactured in the same manner as in Example 1, except that Li5ZrVCl was used instead of Li6PS5Cl as the SE layer (solid electrolyte layer).

[0093]

[0094] Example 5

[0095] An all-solid-state secondary battery was manufactured in the same manner as in Example 2, except that Li5ZrVCl was used instead of Li6PS5Cl as the SE layer (solid electrolyte layer).

[0096]

[0097] Example 6

[0098] An all-solid-state secondary battery was manufactured in the same manner as in Example 3, except that Li5ZrVCl was used instead of Li6PS5Cl as the SE layer (solid electrolyte layer).

[0099]

[0100] Experimental Example 1

[0101] The change in current density according to voltage change was measured for Li6PS5Cl and Li5ZrVCl used as solid electrolytes in the examples, and is shown in Figs. 1 and 2, respectively.

[0102] Referring to Figure 1, Li6PS5Cl, a sulfide-based solid electrolyte, begins to oxidize at 2.14 V, accelerates (peaks occur) at 2.8 V, and electrolyte decomposition continues even in the section after 4.0 V.

[0103] On the other hand, referring to Fig. 2, the chloride-based solid electrolyte Li5ZrVCl begins to oxidize at 2.5 V, accelerates (peaks) at 3.7 V, and continues to decompose electrolyte even after 4.0 V, but the degree of electrolyte decomposition is very low compared to Li6PS5Cl. Specifically, in terms of the unit scale of the graph, the y-axis current density of Fig. 2 is about 1 / 10 the size of the y-axis current density of Fig. 1, as can be seen in the figures of the drawing, and Li5ZrVCl can minimize electrolyte decomposition with an oxidation current that is more than 15 times lower than that of Li6PS5Cl.

[0104]

[0105] Experimental Example 2

[0106] After aging for 6 hours at room temperature for the all-solid-state secondary batteries manufactured in Comparative Examples 1 to 8 and Examples 1 to 6, a charge-discharge test was performed, and the results, including resistance, are shown in Table 1 below. The capacity evaluation was performed based on 200 mAh / g at a 0.1C rate, and the charge-discharge conditions were constant current (CC) / constant voltage (CV) in the voltage range of 2.5 V to 4.3 V (vs. Li+).

[0107]

[0108] The results in Table 1 above confirmed the following facts.

[0109]

[0110] First, referring to the results of Comparative Example 1, it can be confirmed that when only Li5ZrVCl is added during the manufacture of a composite anode, the resistance is high and the ionic conductivity is poor.

[0111] Second, referring to the results of Examples 1 to 3, it can be confirmed that when the chloride-based solid electrolyte is included in the same or greater amount as the sulfide-based solid electrolyte, the resistance is low and the life characteristics are improved.

[0112] Third, referring to the results of Comparative Examples 2 to 4, when the sulfide-based solid electrolyte is included in greater amounts than the chloride-based solid electrolyte, it can be confirmed that the life characteristics are worsened compared to Comparative Example 1, even though the sulfide-based solid electrolyte and the chloride-based solid electrolyte are used together.

[0113] Fourth, referring to the results of Comparative Examples 5 and 6, it can be seen that there is no significant difference when compared to Comparative Example 1, which uses only Li5ZrVCl, even when using solid electrolytes such as Li3YBr6, Li3ZrCl5O, etc. This fact, when considered together with the results of Examples 1 to 3, suggests that when Li5ZrVCl is complexed with a sulfide-based solid electrolyte, the resistance is low and the life characteristics are improved due to high compatibility.

[0114] Fifth, referring to the results of Comparative Examples 7 and 8, Li3YBr6 has a low oxidation peak range (3.4 V) and Li3ZrCl5O has a high oxidation peak range (4.6 V). It can be seen that the solid electrolyte with a low oxidation peak range has little effect on improving the life characteristics even when composited, and the solid electrolyte with an excessively high oxidation peak range has poor compatibility with the sulfide-based solid electrolyte, resulting in high resistance.

[0115] Sixth, referring to the results of Examples 4 to 6, it can be confirmed that when a chloride-based solid electrolyte is used as the solid electrolyte of the electrolyte layer while including more chloride-based solid electrolyte in the anode, the resistance increases slightly, but the life characteristics are significantly improved.

[0116]

[0117] The present invention is not limited to the above-described embodiments, but can be manufactured in a variety of different forms. Those skilled in the art will appreciate that the present invention can be implemented in other specific forms without altering the technical spirit or essential characteristics of the present invention. Therefore, the embodiments described above should be understood as illustrative in all respects and not restrictive.

Claims

1. Positive electrode active material; and Composite electrolyte of a sulfide-based solid electrolyte and a transition metal-containing halide-based solid electrolyte; A composite anode for an all-solid-state secondary battery, characterized by including:

2. In paragraph 1, The above sulfide-based solid electrolyte is a composite positive electrode for an all-solid-state secondary battery, characterized in that it includes a solid electrolyte represented by chemical formula 1: Li a P b S c Z d (1) In the above formula, 0 <a≤20, 0<b≤6, 0<c≤20, 0≤d≤8; Z is at least one selected from the group consisting of F, Cl, Br, I, and O.

3. A composite cathode for an all-solid-state secondary battery, characterized in that the sulfide-based solid electrolyte in the second paragraph contains Li6PS5Cl.

4. In paragraph 1, The above chloride-based solid electrolyte is a composite cathode for an all-solid-state secondary battery, characterized in that it includes lithium zirconium vanadium chloride (LZVC) represented by chemical formula 2: Li e Zr f V g Cl h (2) In the above formula, 0 <e≤5, 0<f≤1, 0<g≤1, 0<h≤8.

5. A composite cathode for an all-solid-state secondary battery, characterized in that in the fourth paragraph, the lithium zirconium vanadium chloride (LZVC) is Li5ZrVCl.

6. A composite anode for an all-solid-state secondary battery, characterized in that the voltage range at which an oxidation peak of the chloride-based solid electrolyte occurs in the first paragraph is 3.5 to 3.8 V.

7. A composite anode for an all-solid-state secondary battery, characterized in that, in the first paragraph, when the weight fraction of the sulfide-based solid electrolyte in the composite anode is defined as A wt% and the weight fraction of the chloride-based solid electrolyte is defined as B wt%, B / A is in the range of 1 to 4.

8. A composite cathode for an all-solid-state secondary battery, characterized in that the weight fraction of the sulfide-based solid electrolyte in the 7th paragraph is in the range of 5 to 12.5 wt%.

9. A composite positive electrode for an all-solid-state secondary battery, characterized in that the weight fraction of the chloride-based solid electrolyte in the 7th paragraph is in the range of 12.5 to 20 wt%.

10. A composite anode for an all-solid-state secondary battery, characterized in that the sulfide-based solid electrolyte and the chloride-based solid electrolyte have a difference in voltage at which an oxidation peak occurs in a range of 0.7 to 0.9 V in the first paragraph.

11. In the first paragraph, the oxidation current occurring at the oxidation peak of the sulfide-based solid electrolyte is A mA / cm 2 The oxidation current occurring at the oxidation peak of the chloride-based solid electrolyte is B mA / cm. 2 A composite anode for an all-solid-state secondary battery, characterized in that the range is 15<A / B<19 when defined as .

12. An all-solid-state secondary battery comprising a composite positive electrode, a negative electrode, and an electrolyte layer disposed between the composite positive electrode and the negative electrode according to paragraph 1.

13. An all-solid-state secondary battery according to claim 12, characterized in that the electrolyte layer comprises a chloride-based solid electrolyte.

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