ANTI-DENDRITE NEGATIVE ELECTRODES, AND THE ELECTROCHEMICAL CELLS CONTAINING THEM

Abstract

Disclosed is a negative electrode comprising multiple coated layers to prevent dendrite formation, the process for manufacturing said electrodes and the electrochemical cells and batteries comprising the same.

Claims

1. A negative electrode of an electrochemical cell comprising: a current collector, a number (n) of successively coated layers over the surface of the current collector, the successive coated layers being numbered (i), i being comprised between 1 and n, in this order from the current collector surface, wherein the layer (1) is the closest layer respective to the current collector and the layer (n) is the furthest layer respective to the current collector; wherein n is an integer, equal to or greater than 2, and equal to or lower than 4, wherein the layer (n) has an outer face and an inner face on the opposite side, wherein each of the n coated layers, identical or different comprises one or more metals and/or metal alloys and/or metalloids and/or metalloid alloys, and wherein the inner face of the layer (n) is in contact with the (n−1) layer immediately located beneath the layer (n).

2. The negative electrode according to claim 1, wherein the negative electrode is initially lithium-free in that the negative does not comprise lithium before a first cycling.

3. The negative electrode according to claim 1, which stores lithium after the first cycling: in the form of a lithiated metal alloy within at least one of the coated layers and/or in the form of a layer of elemental lithium coated between the current collector and the closest layer (1).

4. The negative electrode according to claim 1, wherein each layer comprises one or more metals and/or alloys and/or metalloids and/or metalloids alloys selected from Mg, Al, Zn, Cd, Ti, Cr, Mn, Co, Fe, Ag, Au, In, Sn, Pb, Bi, Sb, Si, B, and the alloys thereof.

5. The negative electrode according to claim 1, wherein the n layers are arranged so that layer (i+1) has a higher potential of lithiation than that of layer (i) which is immediately beneath the layer (i+1).

6. The negative electrode according to claim 1, wherein each layer has a thickness comprised between 0.05 and 20 μm.

7. The negative electrode according to claim 1 wherein n is 2.

8. The negative electrode according to claim 1 wherein the layer (n) comprises one or more metals selected from bismuth, indium, antimony and/or their alloys.

9. The negative electrode according to claim 1 wherein the layer (1) closest to the current comprises one or more metals selected from zinc, magnesium and/or their alloys.

10. The negative electrode according to claim 1 wherein the outer face of layer (n) has an increased surface area.

11. The negative electrode according to claim 1 wherein the current collector consists in a material or alloy chosen from the group consisting in copper, nickel, carbon, stainless steel, and the alloys thereof, in shape of foil, mesh, woven or non woven.

12. Process of manufacture of the negative electrode according to claim 1 the process comprising: coating the closest layer (1) on the current collector, and successively coating each following coated layer (i) until layer (n) is coated, and wherein each coating step is identical or different.

13. An electrochemical cell comprising: a positive electrode; a negative electrode according to claim 1; and a solid-state electrolyte layer as a separator between the positive and the negative electrodes.

14. The electrochemical cell according to claim 13 which is a solid-state cell with sulfide-based electrolyte.

15. An electrochemical module comprising at least two cells as defined in claim 13, wherein each cell is electrically connected with one or more cell(s).

16. A battery comprising at least 2 electrochemical cells according to claim 14 connected with each other.

17. The negative electrode according to claim 1, wherein each layer has a thickness comprised between 0.2 and 10 μm.

18. A battery comprising at least one of the electrochemical modules of claim 15.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0096] FIG. 1 shows an example of a Li-free negative electrode of the invention, with its initial structure (A), and changes after 1.sup.st charge (B) and discharge (C), during cycling (D).

[0097] FIG. 2 are scanning electron and optical images of a Li-free negative electrode with deposited layers.

[0098] FIG. 3 illustrates the initial charge of a solid-state cell with various Li-free negative electrodes (Current density 200 μA/cm.sup.2).

[0099] FIG. 3 illustrates a solid-state cell with a Li-free negative electrode based on a Zn layer+Bi layer, during continued cycling at high current densities during charge (Capacity 2.7 mAh/cm.sup.2).

[0100] FIG. 4 illustrates the charge—discharge profiles with increasing current densities of charge.

[0101] FIG. 5 illustrates a solid-state cell with a Li-free negative electrode based on 3 metal layers Zn/Sn/Bi, during cycling with increasing current densities during charge and discharge.

[0102] FIG. 6 illustrates a solid-state cell with a Li-free negative electrode and increased loading/Capacity 4.3 mAh/cm.sup.2 during cycling with increasing current densities.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0103] The following examples are offered for illustration purposes and do not represent all possibilities encompassed by the present invention.

Example 1: Zn/Bi

[0104] A Li-free negative electrode was assembled as follows A layer of Zn which has lithiation potential 0.157 V vs metal Li was deposited directly on Cu current collector by electroplating and then, a layer of Bi which has lithiation potential 0.82 V vs metal Li was deposited on top of Zn layer by slurry coating of nanoparticles with size from 30 nm up to 100 nm, preferably 50 nm.

[0105] Its initial structure and its change during cycling is illustrated in FIG. 1.

[0106] In FIG. 1, (A) depicts its initial structure, (B) depicts the structure after the 1.sup.st charge and (C) after the discharge, where (B) and (C) are reversibly achieved during the following cycling (D).

[0107] As illustrated in Figure (1A), a representative negative electrode in its initial stage comprises a current collector (1) in the form of a Cu foil, coated with the layer (1) depicted by figure (2)), which can comprise typically Zn. On the top of this layer is further coated the second layer (2) (depicted by figure (3)) which can typically be made of Bi.

[0108] During the first charge the initial Bi/Li alloy is formed at potential below 0.82V, after full lithiation of Bi the potential decreased to the level where the lithiation of Zn started. After that lithium is plated to current collector.

[0109] After the first cycling (B), metal lithium is deposited on the current collector in the form of a metal layer (6), whereas the first and second layers are lithiated and comprise lithium alloys, said alloys being formed with their respective constitutive metals. The first layer (2) becomes thus lithiated into alloy layer (5), and the second layer (3) becomes lithiated alloy layer (4).

[0110] After discharge (C), the layer (6) of metal lithium is substantially consumed, and the first and second layers (5) and (6) substantially unchanged or becomes partially lithiated if all metal lithium is consumed.

[0111] The structures depicted in (B) and (C) are obtained reversibly after each cycling.

[0112] On FIG. 2A, it is apparent that the current collector (Cu foil) (1) is coated with deposited layers (7). On FIG. 2B, the surface of the initial Cu foil and the surface of the foil coated with the deposited layers are pictured (E and F, respectively).

[0113] The thickness of each deposited layer is about 1 μm and it is enough to create layers of alloys that prevent lithium dendrite formation and prevent reactivity with electrolytes.

Example 2: Comparison of 2 Layers Zn/Bi with One Zn Layer and No Addition Layer

[0114] Electrochemical cells were prepared with the negative electrodes with different configurations and compositions of layers (2) and (3) as depicted in FIG. 1 above, with a NMC positive electrode (Nickel Manganese Cobalt oxide), with a sulfide electrolyte and sulfide solid-state electrolyte as separator.

[0115] Cathode composite powder comprises a positive electrode active material (LiNi.sub.0.8Mn.sub.0.1Co.sub.0.1O.sub.2), a sulfide-based solid electrolyte, and a conductive material at a mass ratio 70:25:5.

[0116] A press die with ceramic liner and diameter 15 mm was used for electrochemical cells assembling. Initially 70-100 mg of the sulfide-based solid electrolyte powder was evenly spread inside the die and slightly pressed to form a dense pellet. After that, the cathode composite powder was added on one side in an amount corresponding to the required capacity (from 3 up to 4.5 mAh/cm.sup.2). A negative electrode disk was added on the opposite side of solid electrolyte pellet.

[0117] Finally, the electrochemical sell was compacted by warm pressing at 4.6-5 ton/cm.sup.2 and temperature 60-100° C. for 5 min. The press die was fixed in fixture and electrochemical testing started at 20° C. with low current density at 1.sup.st cycle (200 μA/cm.sup.2).

[0118] As apparent from FIG. 3A, during the first charge with relatively low current density (200 μA/cm.sup.2) the Copper foil as current collector without any additional layers creates dendrites almost immediately after about 2 hours (10% of total charge time) or about 8 mAh/g when the cell potential starts to decreasing in result of partial short-circuit after reaching 3.6 V vs Li.

[0119] The coating of one layer of Zn on the top of the Cu foil (FIG. 3B) improves the charge but does not solve the issue. The dendrites appeared only after 8 hours or 85 mAh/g of initial charge.

[0120] The addition of a further layer (Bi) on the top of the Zn layer creates a system described in example which fully solves the issue with dendrite formation (FIG. 3C): During the first charge, the characteristic for Bi plateau appeared and the cell can be charged without dendrite formation and charge and discharge capacities fully corresponded to amount of active material and its theoretical capacity without any evidence of dendrites formation.

[0121] It was further demonstrated that the negative electrode of the invention makes it possible to further increase the current densities during charge as apparent from FIG. 4 illustrates the charge—discharge profiles where current density of charge increased—; 370 μA/cm.sup.2 FIG. 4a; 568 μA/cm.sup.2 FIG. 4b; and 1.1 mA/cm.sup.2 FIG. 4c respectively. FIG. 4 demonstrates that the proposed 2 layers configuration not only prevents dendrite formation at low current densities but also gives possibility to increase current density and decrease charge time.

Example 3: 3 Layers Zn/Sn/Bi and 2 Layers Zn+Sn Alloy/Bi

[0122] Negative electrodes were prepared according to two embodiments: either 3 layers (successive layers of Zn, Sn and Bi, respectively, in this order) or 2 layers (successive layers of Zn—Sn alloy and Bi, respectively, in this order) were coated on the current collector. In this case, the alloy layer may be obtained by the standard Eastwood Electroplating Tin-Zinc System.

[0123] The two systems similarly protect the anode from dendrite formation

Example 4: Zn+Sn Alloy/Pb/Bi

[0124] Cells with negative electrodes with three layers (Zn+Sn alloy/Pb/Bi) NMC based cathodes and sulfide solid-state electrolyte were also prepared. The results illustrated in FIGS. 5 and 6 demonstrated that high current densities 3.2 mA/cm.sup.2 can be achieved at charge without dendrites formation for cells with high loading (4.3 mAh/cm.sup.2) and bigger amount of lithium transferred between electrodes during charge/discharge cycles.

[0125] Results are summarized in the table below:

TABLE-US-00001 # of I.sub.charge Cell Q.sub.charge cycles Current Capacity short before Density Q, circuit, short μA/cm.sup.2 mAh/cm.sup.2 mAh/cm.sup.2 circuit Comment Cu 200 3.2 0.44 0 Short circuited Cu/Zn 200 3.2 2.9 0 during initial charge Cu/Bi 200 3.1 — 5-8 Short circuited during CV charge Cu/Zn/Bi 200 3.1 — >300* Not Short circuited Cu/Zn/Bi 1100 4.3 — >300* Not Short circuited Cu/Zn/Sn/Bi 2000 4.3 >300* Not Short and Cu/Zn + circuited Sn alloy/Bi Cu/Zn + Sn 3200 4.5 — >300* Not Short alloy/Pb/Bi circuited *Cycleability is limited by cathode materials